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Heat Energy and Temperature
Heat Energy and Temperature
It is because it takes different amounts of energy (Joules) to heat 1 kg of different substances by 10C.
So, when different substances are exposed to the same amount of Heat energy, they will change Temperature by different amounts.
When the sun shines, it gives the same amount of energy to both the sand and the water.
They will absorb the same amount of energy, but for this amount of energy, the sand will increase its Temperature more.
This is because Sand has a lower "heat capacity" than water.
This is referred to as the substance's Specific Heat Capacity.
When you hop into your car in the afternoon, touch the different surfaces.
As long as they have all been in the same level of sunlight, they should all be the same temperature, right? But they are not
How about the beach, you walk barefoot on the grass and you watch out for prickles, but it is fine. Walk on the sand and your feet start burning, so you run to the water. The water is cooler. But why? Why is the grass cool, the sand scorching, and the water cold?
They have all been exposed to the same level of heat energy from the sun, so they should all be the same temperature...right?
However, they are not at the same temperature, so something is happening here...
The image above shows that for the same amount of heat energy (Joules), the sand is hotter. But why?
Heat Energy vs Temperature
Heat energy and temperature are separate but related concepts.
Temperature requires particles.
Heat energy can move from the sun to the Earth without any particles.
The sun will give the Earth a set amount of energy per hour. But different substances will get to different temperatures while sitting in the direct sunlight.
Imagine a playground next to the beach. The metal slide will be hot to touch, but the wood will not.
The things that get the hottest the fastest will also get the coldest the fastest. The hot metal slide will be a cold metal slide at night.
Things that heat up the fastest will also cool down the quickest.
Conversely, the things that take the longest to heat up will also take the longest to cool down. Think of your dinner, you are busy, so it starts to go cold - but different parts of your dinner will go colder faster than others. If you are having toast and baked beans for dinner, the toast will go colder faster than the baked beans. But likewise, it is quicker to turn bread into toast than to heat your baked beans.
So:
Heat energy - it is Energy e.g. Infrared Heat Waves from the Sun
Temperature - what happens to the substance when exposed to that Energy
Well, what happens to the substance when it is exposed to Heat Energy? Its molecules start moving Faster!
The faster molecules move, the more Kinetic Energy the molecules have.
So, for different substances, it takes different amounts of Heat Energy to force their molecules to move a certain amount (Kinetic Energy)
The more the molecules move, the more kinetic energy they have; thus the hotter the substance is to touch and the higher its Temperature.
As it says in the graphic scanned page below, Temperature is the Average Kinetic Energy of the Particles in a substance.
Heat Energy is the Total amount of energy of all the particles in the substance.
Have a watch of the above video, it is very very good
Also, if you go to the beach in the afternoon, at low tide, there are rock-pools. Which is warmer, the rock-pools or the ocean? Why?
So, the temperature results from the Kinetic Energy of the molecules in the substance.
Therefore, space has no temperature. But if you were in space in a "Temo" spacesuit, your molecules would absorb the heat energy and move faster. Thus, your temperature will increase to about 2000 °C. Have a watch of the video above.
Heat Energy is the Total amount of energy of all the particles in the substance.
So, imagine you are having a bath. There is a cup for pouring water on your head. You scoop a full cup of bathwater and then leave it on the ledge to the side.
The water in a 400C bath has the same Average kinetic energy as the water in a 400C cup of water. So, it has the same temperature.
But the bath has far greater Total Energy than the cup of water, because it has far greater total water.
Near the end of the bath you remember the cup of water, you pour it on your head to wash away the shampoo, but it is cold!. Both the bath and the cup are exposed to the bathroom atmosphere, so why has the water in the cup gone cold quicker?
It is because the cup of water had less total energy. So, as it was quicker for it to equalize with the bathroom atmosphere than it is for the bath water.
Bath Water Cooling Rate
Large Volume:
Bathwater contains a significant amount of water, requiring more energy to be released to the atmosphere to cool down. So it will take longer to cool down and equalize with the bathroom atmosphere.
Cup of water Cooling Rate:
Smaller Volume:
The water in a cup is in a much smaller volume, requiring less energy to be released to cool down. Therefore, it will cool down and equalize with the bathroom atmosphere more quickly.
Specific Heat Capacity
Specific Heat Capacity
For the same amount Heat Energy from the fire, the Iron Block will change its Temperature by the greatest amount because it has a lower heat capacity than water.
So it will take less energy to change the temperature of 1kg of Iron.
You put two things into the oven for 3 minutes on high:
Metal Roasting Dish
Stone Plate
You then get them out
Which one is hotter?
Which one cools down the fastest?
Why?
Things that heat up quickly will cool down quickly. Think of the metal dish. This is because they have a low specific heat capacity.
So, only small amounts of energy are needed to change their temperature
Give them small amounts of energy, and their temperature increases quickly
They release small amounts of energy, and their temperature drops quickly
Things that have a high heat capacity take ages to heat up. But also take a long time to cool down. Like the stone plate.
It takes a lot of energy for it to increase its temperature, so it does so slowly
It will then release this energy slowly, so its temperature will reduce slowly
This is why metal is used for your stove top, but stone is used for stone grills and Hangi.
Metal
Heats fast = low thermal capacity = cools fast
Stone
Heats slowly = high thermal capacity = cools slowly (eg stone)
The above video is actually REALLY good!
They actually explain the difference between stone and steel in a geeky Science way. You should watch it
The Thermal Capacity is how much energy a substance is capable of absorbing before its temperature increases by 10C
To put it another way:
It is the amount of energy (J) that 1Kg of a substance must absorb or release to change its temperature by 10C
To put it yet another way:
The heat capacity is unique to a particular substance. Different substances have different heat capacities. To calculate the heat capacity of a substance, you measure how much energy you need to use to change 1kg of the mass by 10C in temperature:
Heat capacity (c) = Energy (J) / (1kg x 10C)
Heat capacity (c) = Energy [J] / (Mass [kg] x temperature change [0C])
The bigger the heat capacity number, the more energy it will take to heat up that substance. However, it will also take longer for that substance to release all that heat energy.
If we heat a block of metal with the same mass as a block of water, you will see that the metal will get hotter quicker for the same amount of energy and cool down quicker — this is because it has a lower heat capacity.
But different metals have different Specific heat capacities.
So when exposed to the same amount of heat energy, they will take different amounts of time to reach a specific temperature.
If we take a kettle of boiling water and pour it into a cup. We then add a copper spoon and an aluminum spoon, which one will get hotter faster?
We can use the image to the side and see that the Specific Heat Capacities of the metals are as follows:
Copper: 390J per Kg per degree celcius
Aluminium: 910J per Kg per degree celsius
Energy: specific heat capacity x mass x change in temperature
Without doing the maths, we can see that it takes less energy for Copper to increase its temperature than it does Aluminium. So, it will be the Copper spoon that will get hot faster.
The interactive Below allows you to compare the Specific Heat Capacity of different substances.
Have a play and see what you discover
The interactive above allows you to compare the Specific Heat Capacity of different substances.
What did you discover?
These values show how much heat energy needs to be transferred to each substance for its temperature to increase by 1 degree Celcius
Of the substances sen here, it is water that requires the most energy
Water needs to absorb the most energy to increase its temperature by 10C
Likewise water will release the most energy to decrease its temperature by 10C. Which is why water is used in hot water bottles (rather than a warm lump of copper).
As you can see, each of the different 'states' of water have different Heat Capacities that are 'specific' for that state.
Notice also, that liquid water has a specific heat capacity of 4.2kJ per Kg per degree Celcius
Both of these YouTube clips are VERY good. I strongly recommend that you watch BOTH of them
Latent Heat Capacity
Latent Heat Capacity
Imagine that you are holding onto a piece of ice...........
This is as far as I've gotten to
Sorry
Please refer to your SciPads and the Past Papers on the OLE
Also, there is a good heat ppt on the OLE
Heat Energy Transfer
Heat Energy Transfer
TO DO:
Questions for Energy PowerPoint - done
Questions for Electricity PowerPoint - done
Calculate Eddie above - done
Calculate or explain the Biker - done
Find more Questions for Mechanics - done
Finish Thermal Energy - NOPE - see above
Find questions for Thermal Energy Powerpoint - NOPE - Refer to Past Exam Papers on the OLE
New To do:
Specific Heat Capacity - Done
Latent Heat Capacity
State-changing graphs
Heat Transfer methods - conduction etc
Past papers and questions slideshow
Lectures - for All of Year 11 before Derived Grade Exams 2025
Year 10 pages
Year 9 pages
Lectures for Year 10 page
Lectures for Year 9 page
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