Heat vs. temperature
Heat vs. temperature
- Unit 1: Particles & Pressure
- Unit 2: Forces & Motion
- Unit 3: Energy & Heat
- Unit 4: Electricity
- Unit 5: Magnetism & Electromagnetism
- Unit 6: Waves: Sound & Light
- Unit 7: Scientific Investigations
In this topic you will:
- understand the difference between heat and temperature.
Heat
You will remember that we described thermal energy in Stage 7. Thermal energy can be transferred between objects. Thermal energy can be stored in an object, but the thermal energy that is stored will eventually dissipate into the surroundings. Thermal energy is measured in joules.
When the thermal energy of an object increases, the particles in the object start to vibrate faster. The energy of the particles increases.
Heat is a measure of the energy in the particles.
Heat is the total thermal energy of the vibrating particles in an object.
Look at the glasses of water in the pictures:
The volume of water is the same in both glasses. One has a higher temperature than the other, meaning that the thermal energy (heat) is greater. The water at the higher temperature contains particles that are moving faster. The number of particles in both glasses of water is the same, but the total thermal energy (heat) of the particles in the water with the higher temperature is higher.
The water in both glasses is at the same temperature. There is a larger volume of water in one glass, so it has more particles. As there are more particles, the total thermal energy (heat) of all these particles is greater than in the water with fewer particles. That means the larger volume of water has greater total thermal energy (heat) than the smaller volume, even when their temperatures are the same.
Temperature
Temperature is not the same as heat. Temperature gives us information about two things:
- the direction that thermal energy will be transferred
- the average energy of the particles in an object.
The ice cream in the picture is at a lower temperature than the surroundings.
The ice cream has been taken from a freezer at –20 °C. The air in the room is at 24 °C, which is a temperature difference of 44 °C (from –20 to 24 °C). Thermal energy is transferred from the air to the ice cream because of this temperature difference.
The larger a temperature difference between two objects, the faster the thermal energy transfer.
Temperature also gives us information about the energy of the particles.
Heat tells us about the total energy of the particles.
Temperature tells us the average energy of the particles.
This means temperature is a good way of comparing the particle energy between objects of different size or made from different materials.
Look at the picture of the hot soup and the cold water.
The soup and the water in the picture are made from different materials, so the types of particles are different. The mass and volume of the soup and the water are also different, so the numbers of particles are different.
When we say the temperature of the soup is higher than the temperature of the water, we mean the average energy of the soup particles is higher than the average energy of the water particles.
Another way to think of this is that 100 particles in the soup have more energy than 100 particles in the water.
Heat and temperature in a sparkler
A sparkler is a small hand-held firework.
When you hold a sparkler, some of the sparks may fall on your hand. The sparkler can be at a temperature of about 1000 °C, but one spark does not cause serious burns. Why not?
The reason is the mass of the spark is very small and the temperature difference between the air and the spark is very large.
As there are fewer particles in the spark than in the main part of the sparkler, the total particle energy is much smaller. Therefore, the total thermal energy or heat of the spark is very small.
As the temperature difference between the spark and the air is large, thermal energy will be transferred from the spark to the air quickly. In the short time the spark takes to fall to your skin, its temperature, and heat, have both decreased significantly.
How low can you go?
As the temperature of an object decreases, the particles move more slowly. A scientist called Kelvin in the 1800s predicted that particles would eventually stop moving if the temperature is low enough.
Kelvin also predicted that if particles stop moving, this would be the lowest possible temperature.
Kelvin called this temperature absolute cold. We now call this temperature absolute zero. Absolute zero is –273 °C.
It is not actually possible to make particles stop moving completely, but scientists have created temperatures within billionths of a degree of absolute zero in laboratories!
Remember:
- heat is the total thermal energy in an object, which is the total energy of all the particles
- temperature is the average energy of the particles in an object.
Questions
J °C N m³
Show Answer
J (joule) is the unit of heat.
J °C N m³
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°C (degrees Celsius) is the unit of temperature.
2. The diagram shows two blocks of copper, A and B.
- block A has a mass of 10 g and a temperature of 25 °C
- block B has a mass of 80 g and a temperature of 25 °C
Show Answer
The temperatures of blocks A and B are the same: 25 °C.
Show Answer
Block B contains more heat because it has a greater mass, even though both blocks have the same temperature.
Show Answer
Heat is the total thermal energy of all the vibrating particles in an object.
Show Answer
Temperature is the average energy of the particles in an object.
- A → B only
- A → C only
- A → B and A → C only
- A → B and A → C and B → C
Show Answer
Thermal energy will transfer from hot to cold, so: A → B, A → C, and B → C.
If object X has a higher temperature than object Y,
then X must always have more heat than Y.
Explain your answer.
Show Answer
False. A hotter object does not necessarily have more heat. Heat depends on both temperature and the number of particles (mass). A larger object with lower temperature can have more heat than a smaller, hotter one.
Think Like a Scientist
You will make measurements of both heat and temperature using a joulemeter and thermometer. This is now an individual investigation.
• The apparatus shown in the diagram (joulemeter, thermometer, immersion heater, polystyrene cup, clamp stand, balance, stirrer, stopwatch)
• Do not touch the immersion heater while it is switched on.
• Clamp the immersion heater so that it does not touch the bottom of the cup.
Step 2. Measure and record the initial water temperature.
Step 3. Set the joulemeter to zero or record its current reading.
Step 4. Switch on the immersion heater and start the timer.
Step 5. Stir the water briefly each minute. Measure and record temperature each minute.
Step 6. Record the joulemeter reading every minute.
Step 8. Switch off the heater and allow the apparatus to cool.
Show Answer
Create a table with time, temperature (°C), and energy (J) columns. Enter data for each minute.
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Draw a line graph with energy (J) on the x-axis and temperature (°C) on the y-axis to show the heating trend.
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Temperature increased steadily with energy input, showing a roughly linear relationship.
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1. Mass of water
2. Power of the heater
3. Type of cup used
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1. Heating the cup
2. Heat loss to air
3. Heat conducted into the thermometer or stirrer
Show Answer
1. Use a lid on the cup
2. Add insulation around the cup to reduce heat loss
Decide how well you did each of these things:
- Making measurements at the correct time
- Recording results in a table
- Drawing the graph of the results