People often think of temperature as how hot or cold something is. But what exactly is temperature?
 

Temperature is a measure of kinetic energy. Every substance is made up of particles. The temperature of a substance is related to the kinetic energies of these particles. If a substance is hot, its particles tend to have a large amount of kinetic energy.
The particles in a substance have kinetic energy because they are moving. The particles are constantly in motion, even if the substance does not appear to be moving.

Select all of the statements that are true about the rubber ball shown above.
    

Temperature is a measure of the kinetic energies of the particles in a substance. However, because the particles in a substance move at different speeds, the particles can have different amounts of kinetic energy. So, what does temperature actually measure?
Temperature measures the average kinetic energy of the particles in a substance. When the particles in a substance have a higher average kinetic energy, the substance has a higher temperature.
Imagine a substance made up of 1,000 particles. Which of these describes the average kinetic energy of the particles?
   

A substance has a higher temperature when its particles have a higher average kinetic energy.
Imagine two different substances that are both pure, meaning they each contain only one type of matter. Each substance has a different temperature.
Which two properties determine which substance has the higher temperature?  

Consider the same two pure samples of gas.   

The particles in sample A have a higher average kinetic energy than the particles in sample B.
Which sample has the higher temperature?
    

Imagine two pure samples of gas in identical closed containers: sample A and sample B. Sample A has a higher temperature than sample B.
Each of the statements below is true about the samples. Which statements describe a property that contributes to the difference in temperature? Select all that apply.   

Think about what you've learned about how particle motion is related to temperature.
Select all of the statements that are true.
    

A substance has a higher temperature when its particles have a higher average kinetic energy.
Imagine two different substances that are both pure, meaning they each contain only one type of matter. Each substance has a different temperature.
Which two properties determine which substance has the higher temperature?
   

Like all substances, gases are made up of moving particles.
The diagrams below show two pure samples of gas in identical closed containers. The colored balls represent the particles in each sample.  

The mass of each particle is the same. The particles in sample B have a lower average speed than the particles in sample A.
Which particles have the lower average kinetic energy?
  

The diagrams below show two pure samples of gas in identical closed containers.  

Each particle in sample B has more mass than each particle in sample A. All of the particles are moving at the same average speed.
Which sample has the lower temperature?  

Particles in each state of matter behave differently because they have different amounts of thermal energy. 

In a solid, the particles are held together tightly, and they do not move around freely. Because the particles stay in about the same place, a solid generally keeps a certain shape.
Even though particles in a solid cannot move past one another, they are not completely still. The particles are constantly vibrating, or moving back and forth, in place.

Select all the true statements.
   

What happens when you heat a solid? Heating a substance increases its thermal energy. When the particles in a solid have more thermal energy, they vibrate more quickly, and the temperature of the substance goes up. Once the substance reaches a certain temperature, called its melting point, the substance can begin to change state.
As more thermal energy is added to the substance, its particles gain enough thermal energy to move around more freely. The particles remain close together, but they are able to slide past one another. When all of the particles have broken out of their fixed positions, the substance has changed state.  

Which of the following happen during this change of state? Select all that apply.  

What happens when you heat a liquid? The particles begin to slide past one another more and more quickly, and the temperature of the substance goes up. When the temperature reaches the substance's boiling point, the particles have enough thermal energy to begin moving far apart and escaping the liquid.

Which of the following can happen when a liquid is heated? Select all that apply.
  

What is true about the particles in a substance? Select all that apply.