In the last chapter we looked at thermal systems which transfer energy. This chapter expands on this and looks at the unlike ways that thermal energy is transferred betwixt different objects.
It is important to sympathise the difference betwixt estrus, equally a concept, and temperature. Temperature is a measure of how hot or common cold an object is; information technology is a measure of the boilerplate kinetic free energy of the particles of a substance. Heat is the energy transferred between two objects every bit a consequence of the temperature departure between them. Information technology is also true when energy is transferred between a system and the surround equally a consequence of the temperature deviation between them. Temperature is measured in degrees Celsius (°C) or degrees Kelvin (K) while estrus is measured in joules (J).
3.1 Heating as a transfer of energy (0.five hours)
three.2 Conduction (2 hours)
Tasks
Skills
Recommendation
Activeness: Conduction through a metallic rod
Experimentation, ascertainment
Suggested
Investigation: Do all materials conduct rut in the same way?
Hypothesising, investigating, evaluating
Suggested
Investigation: Which metals are the best conductors of heat?
What is the difference between heat and temperature?
How does a heater warm up a cold room?
Why can the Sun brand us warm?
Why does my cold drink become warm?
Heating as a transfer of energy
thermal
estrus
temperature
In the last chapter we looked at thermal systems. The thermal free energy of an object is the amount of energy it has within of information technology, in other words, its internal energy. In a thermal system, thermal energy is transferred from i object to another. Rut is the transfer of thermal energy from a system to its surroundings or from one object to another. This transfer of energy is from the object at a higher temperature to the object at a lower temperature.
It is very important to know that, in science, estrus and temperature are non the same thing.
Heat is the transfer of thermal energy from a organization to its environs or from one object to another as a consequence of a deviation in temperature. Oestrus is measured in joules (J). This is because oestrus is a transfer of energy.
Temperature is a measure out of how hot or cold a substance feels and it is measured in degrees Celsius (°C). Temperature is a measure of the boilerplate kinetic energy of the particles in an object or organization. Nosotros utilize a thermometer to mensurate the temperature of an object or substance.
Consummate the following table to summarize the differences between rut and temperature
Estrus
Temperature
Definition
Unit of measurement
Symbol for unit of measurement
Hither is the completed table:
Estrus
Temperature
Definition
The transfer of energy from a hotter object to a colder object, or from a system to its surroundings
A measure of how hot or cold a substance feels. A measure out of the average kinetic free energy of the particles of a substance.
Unit of measurement
Joules
degrees Celsius
Symbol for unit
J
°C
Rut is the transfer of energy. During energy transfer, the energy moves from the hotter object to the colder object. This means that the hotter object will cool down and the colder object will warm upward. The energy transfer will proceed until both objects are at the same temperature.
There are 3 means in which thermal energy can be transferred from one object/substance to another, or from a system to its surroundings:
Conduction
Convection
Radiation
A rap song to introduce you to (and help y'all remember!) conduction, convection and radiation.
Let's have a wait at these in more detail.
Conduction
conduction
conductor
insulator
A suggestion to introduce this topic is to enquire learners what happens to a metal teaspoon when they put it in their hot beverage. If possible, demonstrate this briefly in class, even with a hot glass of water and a metal rod. In addition, use a plastic teaspoon to demonstrate the deviation as plastic is an insulator.
Have yous noticed that when you put a cold, metal teaspoon into your hot cup of tea, the teaspoon handle also warms upwards after a while? Have you always wondered how this warmth "moved" from the hot tea to the cold teaspoon and warmed it up? This is one way in which free energy is transferred and this is called conduction. Let'due south find out how it works.
How does the handle of the metal teaspoon become hot when in a cup of tea?
When energy is transferred to an object, the energy of the particles increases. This means the particles have more kinetic energy and they get-go to movement and vibrate faster. As the particles are moving faster they "bump" into other particles and transfer some of their energy to those neighbouring particles. In this style, the energy is transferred through the substance to the other end. This process is called conduction. The particles comport the energy through the substance, equally shown in the diagram.
Allow's demonstrate this practically.
Conduction through a metal rod
Fix this demonstration up in front of the course as you starting time to talk virtually conduction.
MATERIALS:
Bunsen burner
metal rod
Vaseline
paper clips, drawing pins or safety pins
ii wooden stands, or a stack of books or blocks of wood to create the 2 stands on either side
two pegs
INSTRUCTIONS:
Set the apparatus up equally shown in the diagram.
Encompass the rod in Vaseline and place it between the two stands with pegs to forestall it from rolling and agree it in place. The rod must be extending past the left hand upright and the Bunsen burner placed here so that the Vaseline does not cook due to radiation from the Bunsen burner, but rather conduction along the metallic rod.
Attach the newspaper clips or drawing pins to the rod by sticking them into the Vaseline.
Light the Bunsen burner and oestrus the one end of the rod.
Watch every bit the paper pins or pins driblet off one past 1 as the free energy is conducted through the rod.
INSTRUCTIONS:
Your teacher will set upwardly the demonstration as in the diagram below.
Observe what happens to the pins or newspaper clips equally the Bunsen burner is lit and rut is applied to ane end of the metal rod.
As an extension exercise you could include another investigation in which you mensurate the rate of energy conduction along a metal rod. Repeat the experiment placing drawing pins at 5cm intervals on a long metal rod. Clamp the metallic rod and heat one end over a Bunsen burner. Apply a stopwatch to fourth dimension how long it takes for each drawing pin to drop and record the results on a graph. This could be further extended past using different metals and putting all the results on a single set of axes. The gradient of the graphs would give the charge per unit of heat conduction.
QUESTIONS:
When the Bunsen burner is lit, what happens to the rod just above it?
Energy is transferred to the metal of the rod just in a higher place information technology. The thermal free energy of this part of the rod increases and the rod becomes hot.
Which pin or paperclip dropped off the metal rod first? The 1 closest to or furthest from the Bunsen burner?
The one closest to the Bunsen burner dropped off kickoff.
What does this tell united states of america about the way in which rut is conducted along the rod?
The heat is transferred from where information technology is hottest to the colder end of the rod.
Allow's remember virtually the teaspoon in the tea again. The tea is hot and the metal spoon is cold. When yous put the metallic teaspoon into the hot tea some of the thermal energy from the tea is transferred to the metal particles. The metal particles get-go to vibrate faster and collide with their neighbouring particles. These collisions spread the thermal energy up through the teaspoon. This makes the handle of the teaspoon experience hot.
Conduction is the transfer of thermal free energy between objects that are touching. In the teaspoon example, the particles of the tea are touching the particles of the metallic spoon, which in turn are touching each other, and this is how rut is conducted from i object to the other.
Do all materials conduct heat in the same style? Let's find out.
Misconceptions about temperature. Why do you retrieve your carpet feels warmer than tiles in winter? Lookout this video to observe out.
In response to the video in the margin box about why your carpet feels warmer than the tiles in winter, you tin come dorsum to this question after yous accept performed the following investigation, and besides looked at the example of the cake tin and the cake straight out of the oven. You can lead the discussion in the post-obit way:
Start off by request learners why they would prefer to stand on a carpet in winter rather than the tiles. They would probably answer that the carpet feels warmer.
Follow this up by asking them what they think the temperatures of each surface is. Learners might say that they call up the tiles are at a lower temperature than the carpeting because it feels colder. This is incorrect as the tiles and the carpet will be at the same temperature as they take both been in the aforementioned environment for a while and so will be at the aforementioned temperature.
However, if you pose this question to learners over again after doing the following investigation and also later on looking at the cake and cake tin example, they might so realise that this is another instance of a departure in electrical conductivity.
Namely, the tiles and the carpeting are both at the same temperature, merely the tiles are a ameliorate usher of energy and so they conduct heat at a faster rate away from your feet than the carpet would, making the tiles feel colder, when in bodily fact they are at the same temperature.
Exercise all materials conduct rut in the same mode?
This investigation volition testify the learners that metals conduct heat meliorate than non-metals. If possible, scout the Veritasium video provided in the visit link earlier class about the misconceptions surrounding temperature and which demonstrates this action. Commencement off by asking learners to feel the blocks and ask which ane feels colder. The aluminium block will feel colder. And so ask them which cake they think will melt the ice cube the fastest. equally in the video, nigh people think that the water ice cube volition melt faster on the plastic block as it feels warmer than the aluminium block. However, this is a misconception, and will be demonstrated in the activity that it is in fact the aluminium cake which causes the ice cube to melt faster equally metals are a better conductors of heat.
AIM: To investigate which materials are the best conductors of heat.
In this investigation, we will be placing an ice cube on a plastic cake and on an aluminium cake and observing which ice cube melts the fastest.
HYPOTHESIS: Write a hypothesis for this investigation. Which block do you think will melt the ice cube the fastest?
Learners might hypothesize that the ice cube will melt faster on the plastic than the aluminium block. If they do, make sure that they come up dorsum to decline their hypothesis and revise it.
MATERIALS AND APPARATUS:
a plastic block
an aluminium cake
water ice cubes
a plastic band to keep the ice cube in identify on the block
You can use any piece of plastic and aluminium (or other metal) that y'all can discover. if possible, use a circular ring to stop the melted water from spilling.
METHOD:
Get-go feel the plastic block and the aluminium block. Draw how they feel.
Learners will note that the plastic block feels warmer than the metal block.
Identify an ice cube onto each block and detect what happens.
OBSERVATIONS:
Which ice cube starts to melt get-go and the fastest?
The water ice cube on the aluminium/metal block melts first.
Is this what you lot thought would happen? Refer back to your hypothesis.
Learner-dependent answer. Most people generally have the misconception that the ice cube will melt faster on the plastic block, rather than the metal block.
CONCLUSIONS:
What can you conclude about which textile (the plastic or the metal) is the best usher of heat?
Metal is a improve usher of heat than plastic as the ice cube on the metal melted first.
Nosotros will discuss this in the next paragraph about why this happens.
And so how does this piece of work? This is to do with thermal conductivity, the charge per unit at which oestrus is conducted from ane object to another.
When you originally felt the blocks, you felt that the plastic cake was warmer. But, what we observed is that the aluminium or metal block melted the ice cube faster. This is because the metal block is conducting the heat faster to the ice cube. The plastic block is a worse thermal conductor so less heat is beingness transferred to the water ice cube and and so it does not cook equally fast.
Why then does the aluminium block experience colder than the plastic block?
This is because the aluminium conducts estrus faster away from your manus than the plastic does. Therefore the aluminium block feels colder and the plastic block feels warmer. When you bear upon something, you practise not actually experience the temperature. Rather you experience the rate at which heat is either conducted away from or towards y'all.
Permit'due south recall of another case of baking a block. Imagine you lot have merely finished baking a cake in the oven at 180 °C.
A block baking in the oven in a metal tin can.
When you remove the cake from the oven, which is more likely to fire you more, the metallic cake tin can, or the cake?
The most likely answer is that the block tin will requite yous a more serious burn down.
For the next question, get learners to speculate about what they think nearly the temperature of the cake tin and the bodily tin. Many people have the misconception that the tin can is hotter than the block as information technology feels hotter. They are actually at the same temperature as they accept both been baking at 180 °C.
Do you recollect the cake and the tin are at the same temperature when you lot remove them from the oven? Why?
Yes, the cake and the tin can are both at the aforementioned temperature as they have been blistering at 180 oC. Learners might be inclined to say that the can is at a higher temperature than the cake every bit it feels hotter and the metal tin volition give yous a more than serious fire than the actual block. This is a misconception and yous must talk over this. As with the example of the aluminium and plastic block, the cake tin and the block are at the aforementioned temperature. Simply, the metal tin conducts oestrus faster towards your hand than the cake does. Therefore, the metal tin can will feel hotter and is more probable to give you a serious burn than the block does. When yous touch something, you exercise not really feel the temperature. Rather you lot feel the charge per unit at which rut is either conducted away from or towards y'all.
If y'all take the opportunity, lookout man the video in theVisit margin box by typing the link into your internet browser, even on your mobile phone. This video demonstrates the cake and cake tin example.
What we have seen here is another case of thermal conductivity. The tin will conduct estrus much faster to your hand than the block, and so the can volition burn you, only the block will non. The tin and the cake are at the aforementioned temperature.
So what take we learnt? Metals carry heat better than non-metals.
There are substances that allow thermal energy to be conducted through them and so they are chosen conductors.
There are substances that practice not let thermal energy to be conducted through them and so they are called insulators.
This links dorsum to what we learned in Matter and Materials about the properties of materials and how their properties decide their uses. Remind learners of the activities they did in Matter and Materials, especially linked to electrical conductivity.
Call back, but because a fabricfeels colder, does not mean it has a lower temperature. It may merely be that it is conducting heat faster away from your hand.
Now that nosotros know that metals are expert conductors of heat, exercise you think all metals deport rut equally well? Let'south investigate which metals are better conductors.
Which metals are the best conductors of heat?
Nosotros are going to see which metal is the better conductor of thermal free energy. To do this we volition come across which metal becomes hot beginning.
Make sure yous know how to use a Bunsen burner safely.
Now that we have established that metals conduct heat energy better than non-metals, the learners volition investigate which metals are the best conductors of heat. This investigation requires more heat than the previous one and so the learners should non test the conduction with their fingers.
Spend a few minutes before the learners brainstorm past demonstrating the right procedure for lighting a Bunsen burner. There are many dissimilar instructional videos on the internet, such as the one identified in the visit box in the margin. Hither are a list of instructions for your reference:
Ensure that you are working on an appropriate surface, such equally a fireproof mat, and that it is clean and uncluttered.
Make certain that the gas tube is in good condition and not perishing.
Connect the to the gas outlet deeply and make sure it won't easily come off if moving the Bunsen burner around.
Make certain that the collar at the base of operations of the Bunsen burner and the air hole are closed.
First low-cal your match, holding information technology abroad from the Bunsen burner.
Plow on the gas with your other hand and bring the lucifer to the Bunsen burner to light information technology.
Adjust the air hole by opening it and so that the flame becomes hotter.
Adjust the intensity of the flame using the collar at the bottom.
You can ask the learners to draw posters explaining how to light a Bunsen burner every bit an additional practise if you feel they demand the extra exercise and reminders.
Remember that the tripods and metallic rods that the learners use will become quite hot during this experiment. Make sure to allow the apparatus to cool before packing information technology away.
AIM: To identify whether some metals are better conductors of heat than other metals.
IDENTIFY VARIABLES :
Read through the method and look carefully at the diagram for the investigation to identify the different variables required.
Which variable are you going to change?
Material beingness tested i.e. fe, copper, contumely or aluminium
What exercise we call the variable that you are going to change?
This would be the independent variable
Which variable are you going to measure?
Time taken for the drawing pin to driblet.
What practise we phone call the variable that you are going to measure?
Which variables must be kept the same?
Length and thickness of the material should be the same for each material used. Altitude of the drawing pivot from the oestrus source.
What do nosotros call the variables which must be kept the same?
HYPOTHESIS:
Write a hypothesis for this investigation.
Learner-dependent answer. Learners tin can hypothesise nearly which metal they call back volition be the best conductor, for example, the copper rod will exist the all-time usher.
MATERIALS AND Apparatus:
Bunsen burner
Vaseline
copper, fe, contumely and aluminium rod
stopwatch
cartoon pins
tripod
paper-thin or newspaper
matches
The materials listed hither are a suggestion. Yous can apply alternative apparatus to still do this investigation. For instance, a spirit burner could as well be used to heat the rods. If yous do not accept a tripod stand up, y'all can place the metal rods on another stand, such as a block of wood, with the ends sticking out one side to notwithstanding reach over the Bunsen burner. Paper clips can also be used instead of cartoon pins. The blazon of metals are non important equally long every bit you have different metals of the same length.
METHOD:
Stick the flat end of a cartoon pin to the end of each of the metal rods using the Vaseline. Endeavor to use the aforementioned amount of Vaseline for each drawing pin.
Place the paper-thin on the tripod.
Residual the metallic rods on the cardboard so that one end of each is over the Bunsen burner.
Light the Bunsen burner.
Using a stopwatch, measure how long it takes for each of the pins to drop off.
Record your results in the table.
Draw a bar graph to illustrate your results.
The cardboard is an insulator and will cease the estrus from the rods transferring to the tripod itself. The loss of oestrus from the rods could affect the results.
RESULTS AND OBSERVATIONS:
Record your results in the following tabular array.
Type of metal
Fourth dimension taken for pin to drop off (seconds)
fe
copper
contumely
aluminium
Now describe a bar graph to prove your results. Do not forget to give your graph a heading to draw what information technology represents.
Which variable should exist on the horizontal x-axis?
The blazon of textile should be on the horizontal centrality. This is the contained variable.
Which variable should be on the vertical axis?
The time taken for the drawing pin to to fall off should be on the vertical axis. This is the dependent variable.
Why do you think that a bar graph is suitable for this investigation?
The independent variable/type of material is not a number value and and so it does non need a number line. A bar graph is used to correspond non-number or non-continuous data.
The independent variable is always drawn on the x-centrality with the dependent variable on the y-axis. Both axes must be labelled and prove the units of measurement. The graph should have a heading.
An instance ready of information is given hither with the accompanying bar graph every bit a reference. Your results may vary from these presented here.
Type of metal
Time taken for pin to driblet off (seconds)
fe
60
copper
xxx
contumely
50
aluminium
twoscore
Assay :
Which bar on your graph is the longest?
The longest bar should be the atomic number 26.
Which bar is the shortest?
The shortest bar should exist the copper.
Write down the materials in order of how fast they conducted heat from the quickest to the slowest.
Activity-dependent answer.
Why does the Vaseline melt?
The heat is transferred by conduction through the metal rod and to the Vaseline causing an increment in its temperature and and then a change of state (solid to liquid).
Why do you think it was necessary to identify the piece of cardboard or paper on the tripod stand underneath the metal rods. Hint: The tripod stand is also fabricated of metal.
The paper-thin acts as an insulator to prevent heat from transferring to the stand from the rods. For the purpose of this experiment, the oestrus should transfer down to the unlike metallic rods only.
Why do yous think it is necessary to use the same amount of Vaseline on the ends of each rod?
This is so that the exam is fair, otherwise some drawing pins might be stuck on better than others, leading to inaccurate results.
Do you remember we could have performed this investigation if our rods were of different lengths? Why?
No, otherwise it would not be a fair test as the heat will have to be conducted further in some rods than in others, leading to inaccurate results.
EVALUATION:
It is always important to evaluate our investigations to run across if there is anything nosotros would change or better on.
Is there anything that went incorrect in your investigation that you could have prevented?
Learner-dependent answer.
If you were to repeat this investigation, what would you lot change?
Learner-dependent answer. Examples include: repeating the aforementioned experiment three times and averaging the results, increasing the number of metals tested.
CONCLUSIONS:
Write a conclusion for this investigation about which metallic is the all-time usher of heat.
This respond will depend on their experimental results, and the exact metals which yous used in the investigation.
In this department we looked at how heat is conducted through metal rods and other objects. These were all solid objects. How is energy transferred through liquids or gases? Allow's observe out in the side by side section.
Convection
convection
convection current
As an introduction to this section, you can simulate the "sitting in a bathroom" concept by filling a rectangular plastic tub or small water tank with cold water and so pouring hot water into 1 side. Invite the learners to experience the cold side of the tub and so experience it a few minutes later.
If you can get hold of a lava lamp, this can brand a very heady introduction to the lesson. You can turn the lights off and place the lava lamp on your desk for when learners come up into the class. You tin can so explicate that you are going to notice out why the blobs rise and so fall back downward in the lava lamp. If you practice non have a lava lamp, you tin can also play this video:
Recall of a pot of h2o on a stove. Only the bottom of the pot touches the stove plate, just all of the water inside the pot, even the water not touching the sides, becomes warmer. How does the energy transfer throughout the h2o in the pot? The transfer of energy is because of convection.
Permit's do an activity that will aid united states of america to visualise how convection occurs.
Convection in water
Colourful convection currents (video)
MATERIALS:
200 ml glass beaker
potassium permanganate
Bunsen or spirit burner, tripod stand, wire gauze
Have annotation that you only demand a few grains of potassium permanganate, otherwise y'all will non see anything.
An culling to the above materials is the post-obit:
Cut the cervix of a transparent 4 or 5l container.
Fill up the container three quarters with cold tap h2o.
Put coloured hot h2o (can be coloured with food colouring) into a small bottle with a chapeau that is easy to remove. Close the lid.
Lower the small-scale canteen into the container.
Gently open up information technology once lowered, and then gently accept out your hand from the container, with the lid.
Observe that the coloured hot h2o rises from the pocket-size bottle, through the cold water, then drops down again as information technology cools on its manner up - notice the convection currents.
INSTRUCTIONS:
Learners must not just throw the potassium permanganate into the water. It is important that they identify information technology advisedly in one side of the bottom of the beaker so that they can run across how the currents in the water move.
Half fill the beaker with cold tap water.
Advisedly put a small amount of potassium permanganate on i side of the chalice. DO Not STIR.
Oestrus the water directly nether the side of the beaker with potassium permanganate with a Bunsen/spirit burner and observe what happens.
Ready a command experiment and place a few grains of potassium permanganate into the bottom of a beaker filled with water. Do not oestrus this beaker and observe what happens.
QUESTIONS:
What did you see as the water started to warm up in the beaker that was heated? Draw a picture to show what you lot run across.
Learners should see the purple from the dissolved potassium permanganate moving in a circle upwards through the water.
What is happening to the potassium permanganate in this beaker?
As the potassium permanganate dissolves in the water it is existence dragged through the h2o.
Tin you explicate the pattern you saw?
The warm h2o is rising and existence replaced by libation h2o.
NOTE:
At this point the learners are not aware of the theory behind convection currents and so their answers will exist quite simple.
Compare this to the chalice which was not heated. What did yous observe in this beaker?
The potassium permanganate volition dissolve, just it will non form rising currents. It will lengthened evenly and densely at the bottom of the beaker. Over a long fourth dimension it will spread out evenly throughout the water.
Permit's now explain what we observed in the last activity. Convection is the transfer of thermal energy from one place to another past the motility of gas or liquid particles. How does this happen?
As a gas or liquid is heated, the substance expands. This is considering the particles in liquids and gases gain kinetic energy when they are heated and start to move faster. They therefore take up more infinite every bit the particles movement further autonomously. This causes the heated liquid or gas to movement upwardly and the colder liquid or gas moves downwards. When the warm liquid or gas reaches the top it cools down again and therefore moves dorsum down once again.
Nosotros and so say that the heated liquid or gas is less dumbo as the same particles are now taking upwardly a larger space. Nosotros will learn more about density adjacent twelvemonth in Gr 8.
In the last activity, the water particles gained kinetic free energy and moved apart from each other, therefore taking upward more infinite. This water then moves upwards as it is less dense than the cold water, significant it it lighter than the cold h2o. We were able to observe this every bit the potassium permanganate dissolved in the water and moved with the water particles, and then moved downwards over again as the water cooled.
This movement of liquid or gas, is called a convection current, and energy is transferred from ane expanse in the liquid or gas to another. Take a look at the diagram which shows a convection current.
Does smoke move upwardly or downward?
The learners demand to be careful with this experiment. It is easy to set the T-shaped cardboard alight with the candle and they should be careful not to burn their fingers when lighting the candles every bit well.
MATERIALS:
T-shaped cardboard
candle
twist of paper or splint
chalice
box of matches
INSTRUCTIONS:
You tin drip some wax onto the base of operations then stick the candle onto this to make it stand.
Calorie-free the candle and place information technology within the beaker, to the side of the beaker.
Put the T-shaped cardboard into the chalice so that there is a small gap between the lesser of the chalice and the cardboard.
Light the twisted scroll of newspaper and hold it in the beaker on the opposite side to the candle as shown in the diagram.
Discover what happens to the smoke.
QUESTIONS:
What happens to the smoke from the newspaper?
The smoke is drawn downwardly under the cardboard and upwards next to the candle.
NOTE:
Some of the fume particles may move upwards.
Why exercise you think the smoke moves in this way?
The candle heats the air in a higher place it which creates a convection current which draws the cooler air on the other side of the cardboard towards the candle. This motility of the air particles pulls the fume particles with it. The fume particles permit us to visualise the convection current.
In the last ii activities, nosotros accept observed convection currents in a liquid and in a gas. Convection currents can only form in gases and liquids equally these particles are free to movement effectually. They are not held in fixed positions similar in a solid. Solid particles are held together besides tightly for them to move when heated. Solid particles will only vibrate faster when heated simply will not move from their positions.
The solid particles volition only move from their positions when they accept gained enough kinetic energy for a change of land to occur and the solid melts to become a liquid.
The blobs in a lava lamp motility upwardly and down in the lamp as they first oestrus and expand so reach the surface and cool and so they movement back downward over again.
The blobs in a lava lamp move up and down showing us the convection currents equally the lamp provides the source of estrus at the bottom.
How does a lava lamp piece of work? (video)
Now that we have learned most convection, how tin can we use this in the earth around us? It is interesting to learn well-nigh concepts and theories in science, just it is even more interesting when we discover how this has an influence in our daily lives.
Installation of air heating and cooling systems
Imagine that your teacher has been given a heater and an air-conditioning unit for your classroom. The heater will warm your classroom in winter and the air-conditioner will keep you cool in summer. Y'all need to assist you lot teacher make up one's mind where each item should become in the classroom. Should they go on the wall nearly the ceiling or near the flooring? Should they go adjacent to a window?
This is an photograph of an air conditioner.
INSTRUCTIONS:
Go into groups of 2 or iii.
Talk over where in your classroom you would identify a heater and then that it can effectively heat upwards the room. Describe a diagram to explain your choice.
A heater should be placed nearly the flooring. As it heats the air around it, the warm air will rise and be replaced by absurd air. The cool air is then warmed and rises. This creates a convection current which will warm the unabridged room. The diagram should testify the upward circulation of the warm air.
Talk over where in your classroom yous would install the air-conditioner so that it tin effectively cool the room. Draw a diagram to explicate your choice.
An air-conditioner should be placed well-nigh the ceiling. As it cools the warm air near the ceiling the cool air moves downward towards the flooring and is replaced past warm air from beneath. The warm air is and so cooled past the air-conditioner. This creates a convection current which will cool the unabridged room. The diagram should show the down apportionment of the cool air.
Endeavour to notice an air-conditioner or heating specialist who you can interview. Enquire them to explain the best way to install the air-conditioner and a heater.
We accept at present looked at how free energy is transferred through different materials, whether they are solids (conduction) or liquids and gases (convection). But, what about if there are no particles to transfer the thermal energy? Is in that location still a way for energy to be transferred?
Radiation
radiation
matt
reflect
blot
Have you lot e'er wondered how the Sun is able to warm united states even though information technology is and so far away? The energy is transferred from the Dominicus to everything on the Earth. The Sun does not need to be touching the Earth for the energy to be transferred. Likewise, there is space in betwixt the Earth and the Lord's day. The free energy from the Sun is able to warm us without the Sun ever touching u.s.a..
This transfer of energy is called radiation. It is unlike to conduction or convection equally it does not require objects to be touching each other or the movement of particles.
Radiation comes from the Greek wordradius, meaning a beam of low-cal.
The Sun radiates oestrus in all directions. Free energy is transferred through infinite to World
It takes lite about 8 minutes to travel from the Sun to Earth.
We can also see how oestrus is transferred by radiation here on World, and not just between the Lord's day and the Earth. Let's demonstrate the divergence between radiation and convection using a candle.
Radiation from a candle
A suggestion is to do this as a demonstration and get learners to come up in modest groups. You tin then control how shut they put their hands to the flame. Take notation that oestrus radiates in all directions around the source of thermal energy (including the meridian of the candle). What makes us feel the heat more at the top is the event of convection currents of the hot air moving up. They should start concur their hands above the flame to feel the heat from convection. Then they should concur their hands adjacent to it to feel the rut transfer from radiation. Finally, you lot can too demonstrate conduction using a metal spoon and property it in the flame.
MATERIALS:
candle in a holder
metal spoon or metal rod
matches
INSTRUCTIONS:
Lite a candle and place it in a holder. Your teacher might do this and get groups of you to come at a time to the sit-in.
First hold y'all hand above the candle.
Then hold your hand on the side of the candle.
Reply the post-obit questions.
QUESTIONS:
We know now that heat from a candle will be transferred to the air around information technology. These volition warm up. Where will this air motion to?
The air particles will motility upwardly.
So, when you concur your mitt higher up the candle, what do you feel and why?
When you concord your hand above the candle, the warm air particles transfer the free energy to your hand causing your hand to warm up and you experience the increment in temperature.
But, what about when you hold your hand on the side of the candle? Could you as well experience warmth from the candle?
This is not convection as the air particles do not travel sideways when they warm upward from the flame. So, how is free energy transferred to your paw when you experience the warmth on the side of the candle?
The energy is transferred by radiation.
Lastly, if your instructor placed a metal spoon in the candle flame and you felt the stop, how would it feel later on a little while?
How was the energy transferred from the flame to the end of the spoon?
The energy was transferred by conduction.
This photo shows all three forms of how heat is transferred. Explain which blazon of heat transfer is represented by each hand.
Free energy is transferred in three ways.
The hand on the right holding the spoon represents conduction as the heat is transferred from the flame through the metal of the spoon. The mitt higher up the candle represents convection as heat is transferred from the flame by moving air particles which warm up and rising. The hand above the candle will also experience heat from radiation as estrus is radiated in all directions. The hand on the left next to the candle represents radiations as energy is transferred from the source through space to the mitt.
As nosotros saw in the last activity, energy is transferred from the candle to your hand by convection and by radiation. Have you ever stood next to a huge burn? You will feel the radiating estrus even though the air might be very common cold. This is considering the energy is transferred to y'all by radiations through the spaces betwixt the particles in air.
What about if yous touch a black wall or a white wall? Do y'all recollect in that location is a difference in how different surfaces absorb and reflect radiations? Let'southward detect out by doing an investigation.
Which surfaces absorb the near radiation?
This investigation looks at the fashion different materials absorb radiation or reflect it. It is important that the surface area of each material is kept the same and then that the results are reliable. This investigation will work all-time on a hot, sunny 24-hour interval. Try to observe the sunniest place you lot can on the school grounds in order to conduct this investigation.
We are going to investigate which surfaces blot the most rut, using night coloured paper, light coloured paper and shiny paper, such as aluminium foil. We will use the temperature within an envelope made from each kind of paper equally a measure of the amount of heat the paper absorbed. Why practice you think nosotros tin can do this?
Discuss this with your class as it is important that the understand why they are doing the investigation. When the paper envelope absorbs heat, the energy volition then be transferred to the air inside the envelopes. This will then crusade a ascent in temperature which the thermometer volition show. The more energy that is absorbed, the more than that is transferred to the interior, and the higher the temperature. The newspaper that reflects the most free energy will prove the smallest increase in temperature.
INVESTIGATIVE QUESTION:
Which surfaces will absorb the most radiations from the Sun and therefore increase in temperature the fastest?
VARIABLES
Which variable are y'all going to mensurate?
The temperature of the substance.
What practise we call the variable you have measured?
Which variable are you going to alter?
What do nosotros phone call this variable?
What must exist kept the aforementioned for all the different materials?
The surface surface area of each substance which is exposed to the Dominicus must be the same (ie. the size of the envelope). The length of time that the materials are exposed to the Dominicus.
HYPOTHESIS:
Write a hypothesis for this investigation.
Learner-dependent answer. The hypothesis could be: 'The shiny surface will absorb the least estrus, and the black/night coloured paper will absorb the most.'
MATERIALS AND APPARATUS:
matt blackness newspaper
white paper
aluminium foil
3 booze thermometers
stopwatch or timer
glue or adhesive tape
Yous can also extend the investigation by testing more colours, such as red and yellow to see how they compare.
METHOD:
Fold each piece of paper and aluminium foil into the shape of an envelope.
Put a thermometer into each of the envelopes and record the starting temperature.
Put all the envelopes outside in the Dominicus.
Check the temperature on the thermometers every 2 minutes for sixteen minutes.
Record your results in the table.
Depict a line graph for each envelope on the same set of axes.
RESULTS AND OBSERVATIONS:
The results for this experiment are dependant on the size of the paper envelope that the learners brand as well equally the amount of sunlight falling on the envelopes. The readings may too fluctuate from time to time as a result of cloud roofing.
Record your results in the following table.
Time (minutes)
Temperature in black paper envelope (°C)
Temperature in white newspaper envelope (°C)
Temperature in aluminium foil envelope (°C)
0
two
4
6
8
x
12
fourteen
sixteen
Draw a line graph for each of the envelopes in the infinite below. Do not forget to give your graph a heading.
Time should exist plotted on the horizontal axis with temperature on the vertical axis. Draw three different graphs for the three different materials. Comparison the slopes of the three graphs volition allow the learners to determine which material warmed upwards fastest. The line with the steepest slope heated the fastest.
The black newspaper should increase in temperature the fastest and then it would have the steepest curve. The aluminium envelope should increase in temperature the slowest and take the shallowest bend, with the white paper in betwixt.
The graph should take a title. An example of a suitable title would be 'A comparison of the rate of temperature increase of different surfaces.'
Analysis:
What do you notice about the shapes of the graphs yous drew? Are the graphs direct lines or curves?
Action-dependent answer. The values obtained will depend on the size of the envelopes the learners make besides as the amount of sunlight to which the envelopes were exposed. It is of import that they should run across an increasing trend in the lines of the graph.
Which line on your graph is the steepest? What does this tell us?
The graph representing the black newspaper should be the steepest graph. This ways this envelope increased in temperature the fastest. This is because the black, matt color absorbs the virtually radiation.
Compare your results for the white paper and the shiny surface. What does this tell you.
The envelope made out of aluminium foil should testify the smallest increase in temperature as shiny surfaces reflect heat.
EVALUATION:
Did the investigation run smoothly? Or is in that location anything you would change?
Learner-dependent answer. Learners should discuss the quality of their method and whether they got the results that they expected to get. They could propose repeating the experiment three times and getting an average increment over fourth dimension.
Did you get whatsoever results which did not seem to fit the overall pattern?
Learner-dependent answer. Some learners may get outliers but others may take articulate results with a clear patterns.
CONCLUSION:
Write a decision for your investigation. Remember to refer back to the investigative question that we wanted to answer.
Learners should conclude that black surfaces absorb the most radiation and therefore show the biggest and fastest increase in temperature, whereas shiny surfaces blot the least, as they reverberate the virtually.
Radiation from the Sun is essential to life on Earth, but ultraviolet radiation from the Sun tin can besides be very damaging our peel. Remember to vesture suncream and a hat when outside and avoid being in direct sunlight between 11am and 2pm.
The investigation showed that the dark envelope showed the biggest increase in temperature. The lighter coloured envelope showed a smaller increase in temperature. The envelope made out of a shiny fabric showed the smallest increase in temperature.
And then what have we learnt? Dark colours seem to blot more of the Dominicus'south radiation than light or cogitating colours. So, if yous want to stay warm on a common cold day, night article of clothing will blot more of the available warmth from the Sun's radiation than light colours.
The boilerplate summer temperature in Hotazel, a boondocks in the Northern Greatcoat is most 34 °C. If you lived in Hotazel and needed to buy a new car, would you lot purchase a light or nighttime-coloured motorcar? Explain why.
The all-time colour to purchase would exist a white automobile considering, as seen in the investigation, light colours blot less rut than nighttime colours. And then a light-coloured car will ideally remain the coolest on the inside.
Yous have the option of getting the car sprayed to make the surface more shiny. Do y'all recollect this will help keep the automobile cool in hot, summer months? Explain why.
Yeah, it will assist, as shiny surfaces are more reflective and then more than radiant rut is reflected rather than absorbed, keeping the inside of the car cooler.
Summary
Rut is energy that is transferred from a hotter to a cooler object.
Temperature is a measure of how hot or cold a substance feels.
Heat (energy transfer) occurs in three ways: conduction, convection or radiation.
During conduction, the objects must exist touching each other for energy transfer to take identify.
Some materials, such as metals, conduct heat well. They are called conductors of heat.
Some materials, such as plastics and wood, ho-hum down or prevent conduction. They are called insulators.
Convection is the transfer of energy inside liquids or gases.
A convection electric current refers to the movement of a liquid or gas during free energy transfer. The liquid or gas moves up from the heat source (as it expands) and then downward when the liquid or gas cools (every bit information technology contracts).
Radiation is the transfer of energy where objects do not have to be physically touching. Radiation does non require a medium and tin can have place through empty infinite.
The Lord's day'south energy is transferred to Earth past radiation.
Dark, matt surfaces are good absorbers of radiant rut
Light and shiny surfaces are poor absorbers of radiant heat. Light, shiny surfaces reflect more than radiant oestrus than they absorb.
Concept map
Below is a concept map showing how the dissimilar topics near heat together. You demand to make full in the three unlike ways that energy can be transferred, as discussed in this affiliate, but you cannot just put anyone into any box. You need to study the concepts which come after and explain each manner of transferring energy during heating.
Revision questions
How is energy being transferred in the following photos showing different heating processes? Write down conduction, convection or radiation. Some illustrations may prove more than than one class. [iv marks]
The oestrus from the Sun travels to Earth.
Cooking nutrient on a braai or burn.
Radiation
Convection (and also some radiation)
Boiling water in a metallic pot.
A heater in a room.
Conduction (through the metal) and convection (in the water)
Radiation and convection
In each of the post-obit situations, identify the method of energy transfer taking place (conduction, convection, radiation).
A fireplace has a glass screen in front of it. The person sitting in a chair next to the fireplace chair feels hot due to ________. [i marker]
When you stir your tea with a metal spoon the handle gets hot considering of ________. [1 marker]
When you are lying on the beach your skin feels hot because of _______. [i mark]
radiation
conduction
radiation
Draw energy transfer catamenia charts for the post-obit: You lot purchase a cup of hot chocolate and concord information technology in your hands on a cold winter day. [2 marks]
The energy is transferred from the loving cup to the hands by conduction.
Annotation:
One of the marks is for choosing the correct direction of the energy transfer. The second mark is for drawing information technology in the form of a flow nautical chart.
Your parents have a metal hot water geyser and they are complaining about the amount of free energy needed to keep the h2o hot. What tin can you recommend your parents could do to prevent energy loss from the geyser? Explain your reply. [iv marks]
Metals are practiced conductors of estrus and so the heat from the water is transferred out of the geyser. A (shiny foil) insulating blanket could be used to wrap around the geyser. The air between the coating and the geyser is a poor conductor of heat and so the oestrus loss volition be slower.
Explain why the heating element for a kettle is at the bottom and not at the top. [3 marks]
The heating element is at the bottom because every bit the element transfers free energy to the water, the water expands and moves upwards and the colder water (slower moving particles) will sink to the bottom, forming a convection current This cycle will ensure that all the water is heated as quickly as possible. If the element was at the peak, the water at the lesser would take much longer to eddy.
Annotation:
Learners must mention the term convection current.
Explain why yous retrieve the water boils throughout the kettle pot and not just at the lesser? [2 marks]
The water at the bottom of the pot gets hot and so moves to the top of the pot considering of convection. This allows the cold water to sink to the bottom and heat upwards. This abiding circulation allows all of the water to heat upwards and boil.
Explicate why y'all recollect take-abroad java is sold in styrofoam cups rather than ceramic cups. [2 marks]
Normal ceramic cups are good conductors of heat and and so the energy from the coffee is transferred quickly through the loving cup to the surroundings. The styrofoam is a poor conductor of heat and and so it does not allow the energy from the coffee to motion chop-chop to the surrounding air, so the coffee stays warmer for longer.
Explicate why you think two thin blankets can sometimes be warmer than one thick blanket. [two marks]
Air is trapped betwixt the two blankets. The air is a very poor conductor of rut and and so it becomes an extra insulating layer which slows downwards the loss of energy from your body. One blanket cannot trap equally much air so isn't equally warm as two blankets.
Explain why birds fluff upwards their feathers to stay warm, peculiarly in winter. [ii marks]
Birds fluff up their feathers so that more air gets trapped between the feathers. The air is a poor conductor of heat and so the energy from the birds torso is non transferred to the surroundings.
Why should you place an air conditioner at the peak of a room, most the ceiling, rather than at the bottom near the flooring? [2 marks]
This is considering cold air volition motility downwards, therefore cooling the room, and the hot air will rise and tin therefore be removed by the air conditioner at the top of the room, near the ceiling.
Imagine y'all want to build a pocket-size enclosure for some chickens on your property. You take an exterior surface area for them that is made from spinous wire, and you accept fabricated a pocket-size inside, covered enclosure for them out of bricks and cement which you would similar to pigment. Yous know that information technology can get quite cold in winter in your expanse and then you lot desire the house to be as warm as possible for the chickens. What color paint are yous going to choose to paint the outside of chicken house? Volition information technology exist a dark-coloured paint, such as brown or black, or a calorie-free-coloured paint, such every bit white or yellowish? Explain your choice. [4 marks]
The best choice to keep the house as warm as possible on the inside is a nighttime-coloured paint. This is because the nighttime colours absorb more than radiant rut from the Sun during the day, than the low-cal colours, which reflect rut. The dark paint volition absorb the estrus and information technology volition exist transferred to the air inside of the house, making it warmer, especially during winter.
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