Physics 001.001.002 Thermal Energy

Alignment

Learning Intentions

By the end of the lesson, students will be able to:

• Describe thermal energy, temperature, kinetic energy, heat and internal energy.
• Distinguish between temperature, heat and internal energy using particle-level explanations.
• Explain heating as an energy transfer caused by a temperature difference.
• Use the kinetic particle model to describe why substances feel hotter or colder.

Success Criteria

By the end of the lesson, students have successfully:

• Defined each key term accurately: thermal energy, temperature, kinetic energy, heat and internal energy.
• Explained that temperature is related to the average kinetic energy of particles.
• Explained that internal energy is the total microscopic kinetic and potential energy of particles in a system.
• Identified heat as energy transferred from a hotter system to a colder system.
• Corrected common misconceptions, such as “objects contain heat” or “temperature is the same as thermal energy”.

Syllabus Reference

• Unit 1: Thermal, Nuclear and Electrical Physics
• Topic 1: Heating Processes
• Science Understanding: Kinetic Particle Model and Specific Heat Capacity
• Describe the concepts of thermal energy, temperature, kinetic energy, heat and internal energy.

Phenomenon

A mug of hot chocolate and a swimming pool can both contain thermal energy. The hot chocolate has a much higher temperature, but the swimming pool contains far more particles. This means the swimming pool can have much more total internal energy even though it feels cooler.

Guiding question:

How can a cooler swimming pool contain more internal energy than a hotter cup of hot chocolate?

Key Idea

Matter is made of particles that are constantly moving or vibrating. The faster the particles move on average, the higher the temperature. The total energy stored in the motion and arrangement of particles is internal energy. Heat is not something an object “has”; heat is energy transferred between systems because of a temperature difference.

Concept

The concept and thought that best describes the cause of the phenomenon is below.

Thermal phenomena can be explained using the kinetic particle model. Particles in solids vibrate about fixed positions, particles in liquids move around each other, and particles in gases move freely and rapidly. When energy is transferred to a substance by heating, the particles usually gain kinetic energy, increasing the temperature if there is no phase change.

Temperature describes the average kinetic energy of particles. Internal energy describes the total microscopic energy of all particles in the system, including kinetic energy and potential energy due to particle interactions.

A small hot object may have a high temperature but relatively little internal energy because it has fewer particles. A large cool object may have a lower temperature but much more internal energy because it contains many more particles.

Convention

The key conventions associated with the concept and in the branch of established knowledge is below.

• Temperature is measured in degrees Celsius, , or kelvin, .
• Kelvin is the SI unit for temperature.
• Energy is measured in joules, .
• Kinetic energy is energy due to motion.
• Heat, , means energy transferred due to a temperature difference.
• Heat naturally transfers from a higher temperature region to a lower temperature region.
• A system is the object or group of objects being studied.
• The surroundings are everything outside the system.
• Internal energy, , is the total microscopic kinetic and potential energy of the particles in a system.

Misconceptions

Common misconceptions students have regarding the concept when applying to various situations and solving problems. It could be a conceptual, mathematical or logical misconception.

• Objects “contain heat”. Correction: objects contain internal energy; heat is energy transferred between systems.
• Temperature and thermal energy mean the same thing. Correction: temperature depends on average particle kinetic energy, while internal energy depends on the total energy of all particles.
• A hotter object always has more internal energy than a colder object. Correction: internal energy also depends on mass, number of particles and state of matter.
• Coldness flows from cold objects into warm objects. Correction: energy transfers by heating from hotter objects to colder objects.
• Particles in a solid do not move. Correction: particles in a solid vibrate around fixed positions.

Further Reading

• Kinetic particle model of matter
• Specific heat capacity
• Thermal equilibrium
• First law of thermodynamics
• Phase changes and latent heat

Explicit Instruction

Teacher explanation sequence:

1. Define kinetic energy.

   • Kinetic energy is energy due to motion.
   • At the particle level, atoms and molecules have kinetic energy because they vibrate, rotate or move from place to place.

2. Define temperature.

   • Temperature is a measure of the average kinetic energy of particles in a substance.
   • Higher temperature means particles have greater average kinetic energy.
   • Temperature does not measure the total energy of all particles.

3. Define internal energy.

   • Internal energy is the total microscopic energy stored in the particles of a system.
   • It includes:
     • microscopic kinetic energy from particle motion
     • microscopic potential energy from particle spacing and interactions

4. Define thermal energy.

   • In school physics, thermal energy is often used to describe energy associated with the random motion and arrangement of particles.
   • It is closely related to internal energy.
   • More particles usually means more total thermal energy, even if the average energy per particle is lower.

5. Define heat.

   • Heat is energy transferred from one system to another because of a temperature difference.
   • Heat is a process of energy transfer, not a substance stored inside an object.
   • Once the transfer has occurred, the energy becomes part of the internal energy of the receiving system.

6. Connect the ideas.

   • Adding energy by heating usually increases particle kinetic energy.
   • Increased average kinetic energy means increased temperature.
   • If a phase change occurs, energy may increase internal potential energy without changing temperature.

Key comparison table:

Concept	Meaning	Depends on	Unit
Kinetic energy	Energy due to motion	Speed and mass of particles
Temperature	Average kinetic energy of particles	Average particle motion	or
Internal energy	Total microscopic kinetic and potential energy	Mass, temperature, state and particle interactions
Thermal energy	Energy associated with random particle motion and arrangement	Number of particles and their energies
Heat	Energy transferred due to temperature difference	Temperature difference and transfer pathway

Worked Examples

Worked Example 1

Question:

A cup of tea is at and a swimming pool is at . Which has the higher temperature? Which likely has the greater internal energy?

Solution

Solution: The cup of tea has the higher temperature because its particles have greater average kinetic energy.

The swimming pool likely has the greater internal energy because it contains far more particles. Internal energy depends on the total microscopic energy of all particles, not just the average energy per particle.

Answer:

• Higher temperature: cup of tea
• Greater internal energy: swimming pool

Worked Example 2

Question:

A metal spoon at is placed into soup at . Describe the energy transfer using the terms heat, temperature and internal energy.

Solution

Solution: The soup has the higher temperature, so its particles have a greater average kinetic energy than the particles in the spoon.

Energy is transferred by heating from the hotter soup to the cooler spoon. This energy transfer is called heat.

As energy is transferred to the spoon, the internal energy of the spoon increases. Its particles vibrate more rapidly, so its temperature increases.

Answer: Heat transfers from the soup to the spoon because there is a temperature difference. The spoon’s internal energy increases and its temperature rises.

Worked Example 3

Question:

Two identical blocks are made from the same material. Block A has a mass of and Block B has a mass of . Both are at . Compare their temperature and internal energy.

Solution

Solution: Both blocks have the same temperature, so the average kinetic energy of their particles is the same.

Block B has twice the mass, so it contains more particles. Since internal energy is the total microscopic energy of all particles, Block B has more internal energy.

Answer: Both blocks have the same temperature. Block B has greater internal energy because it contains more particles.

Check for Understanding

Check 1

Question:

Explain the difference between temperature and internal energy.

Solution

Expected response: Temperature is related to the average kinetic energy of particles. Internal energy is the total microscopic kinetic and potential energy of all particles in the system.

Check 2

Question:

Why is it incorrect to say that “a hot object contains heat”?

Solution

Expected response: Heat is energy transferred between systems because of a temperature difference. A hot object contains internal energy, not heat.

Check 3

Question:

A small iron nail and a large iron beam are both at . Which has greater internal energy? Explain.

Solution

Expected response: The iron beam has greater internal energy because it has more mass and therefore more particles. Both objects have the same temperature, meaning their particles have the same average kinetic energy.

Investigation (Alternative to Explicit)

Hypothesis

If two objects have different temperatures and are placed in contact, then energy will transfer from the hotter object to the cooler object until their temperatures become closer, because heat transfers due to a temperature difference.

Data Collection

Practical: Mixing warm and cool water

Materials:

• Beaker
• Measuring cylinder
• Digital thermometer or temperature probe
• Warm water
• Cool water
• Stopwatch
• Stirring rod
• Safety glasses

Method:

1. Measure of cool water and record its temperature.
2. Measure of warm water and record its temperature.
3. Pour both samples into the same beaker.
4. Stir gently.
5. Record the temperature every for .
6. Observe whether the final temperature is between the two starting temperatures.

Safety:

• Use warm water only, not boiling water.
• Wear safety glasses.
• Wipe spills immediately.
• Handle glassware carefully.

Data table:

Time,	Temperature,

Analysis

Students answer:

1. Which water sample had the greater temperature at the start?
2. Which sample had particles with greater average kinetic energy at the start?
3. In which direction did heat transfer?
4. Did the final temperature support the idea that energy was transferred from the warmer water to the cooler water?
5. Why was the final temperature not exactly the average of the two initial temperatures?

Solution

Expected analysis:

• The warm water had the greater initial temperature.
• The warm water particles had greater average kinetic energy.
• Heat transferred from warm water to cool water.
• The mixed water reached a temperature between the two initial temperatures.
• Some energy may have transferred to the beaker, thermometer and surroundings.

Evaluation

Students evaluate:

• Was the thermometer precise enough?
• Was any energy lost to the surroundings?
• Were the volumes of water measured accurately?
• Was the water stirred consistently?
• How could the method be improved?

Solution

Possible improvements:

• Use insulated cups.
• Use a lid.
• Use a temperature probe connected to data-logging software.
• Repeat trials and calculate a mean final temperature.
• Measure mass instead of volume for greater accuracy.

Problems

The following problems are designed to develop conceptual understanding of thermal energy, temperature, kinetic energy, heat and internal energy.

1. Define kinetic energy in terms of particle motion.

2. Explain why temperature is related to average kinetic energy, not total kinetic energy.

3. A cup of coffee at is left on a bench in a room at .

   • a. In which direction does heat transfer?
   • b. What happens to the internal energy of the coffee?
   • c. What happens to the average kinetic energy of the coffee particles?

4. A lake and a cup of boiling water are compared.

   • a. Which has the higher temperature?
   • b. Which probably has the greater internal energy?
   • c. Explain your answer using particles.

5. A student says, “The metal bench feels colder than the wooden bench, so the metal must be at a lower temperature.” Explain why this may be incorrect.

6. Identify whether each statement describes temperature, heat or internal energy:

   • a. Energy transferred from a flame to a saucepan.
   • b. The average kinetic energy of particles in a gas.
   • c. The total microscopic kinetic and potential energy of particles in a block.

7. Explain why a thermometer reading increases when it is placed into hot water.

8. Complete the sentence: Heat transfers naturally from a region of _ temperature to a region of _ temperature.

9. A block of copper and a block of copper are both at . Which has more internal energy? Explain.

10. Explain why internal energy can change even when temperature does not change during a phase change.

Solution

Suggested answers:

1. Kinetic energy is energy due to motion.
2. Temperature describes average particle kinetic energy; total kinetic energy also depends on how many particles are present.
3. Heat transfers from coffee to room; coffee internal energy decreases; average kinetic energy decreases.
4. Boiling water has higher temperature; lake probably has greater internal energy because it contains vastly more particles.
5. The metal may conduct energy away from the hand faster, even if both benches are at the same temperature.
6. a. Heat, b. Temperature, c. Internal energy.
7. Energy transfers from hot water to the thermometer, increasing the internal energy and average kinetic energy of particles in the thermometer.
8. Higher, lower.
9. The block has more internal energy because it contains more particles.
10. Energy changes the arrangement or spacing of particles, increasing potential energy rather than average kinetic energy.

Followup

Self-check

Students complete the following reflection:

• I can define kinetic energy.
• I can explain temperature using the kinetic particle model.
• I can explain why heat is energy transferred, not energy stored.
• I can distinguish between temperature and internal energy.
• I can explain why a large cool object can contain more internal energy than a small hot object.
• I can describe heating as energy transfer due to a temperature difference.

Exit ticket:

1. One sentence: What is temperature?
2. One sentence: What is heat?
3. One sentence: What is internal energy?
4. One example where the hotter object does not have the greater internal energy.

Next Topic

The next topic is heat transfer by conduction, convection and radiation.

Students will learn how energy transfers through solids, liquids, gases and electromagnetic radiation, and how these processes explain everyday phenomena such as cooking, sea breezes, insulation and feeling warmth from the Sun.