To help remember the difference between expansion and contraction, you can think about when you breathe.

• Take a deep breath and feel your lungs get bigger. Your lungs are expanding as they fill with air.

• Now slowly let your breath out and feel your lungs get smaller. Your lungs are contracting as the air leaves.

You can also think about balloons.

• When you blow them up they expand

• When you let the air out they contract

When matter expands it gets bigger and when matter contracts it gets smaller. It is hard to see objects expanding and contracting with our naked eye because these changes are usually so small!

We know that when it is cold or there is a lack of heat energy the particles move slower and the matter contracts.

However, water is the only substance that expands when it gets cold.

• Have you ever put a water bottle in the freezer and forgot about it? What about a can of pop?

• What happened to these objects in the freezer?

We encounter expansion and contraction throughout our everyday lives. It is really important to understand how the particles in matter act when there is a presence or absence of heat energy.

To help you learn more examples of expansion and contraction and why it is important, there are three short videos for you to watch. While you are watching these videos, try to answer the questions that go with each video. These questions can be found in the worksheet to the right and below each video.

Make sure that you understand what is happening to the matter at the particle level. What are the particles doing that makes the matter expand or contract?

You have been hired by the local newspaper to write answers to the science questions that students have submitted. Choose two of the questions below to explain in your own words. They must be different states of matter. For example, this means that you cannot pick two questions about solids.

1. Why does an engineer need to think about expansion and contraction when designing a bridge?

2. Why does my mom run her hand under hot water when she tries to get her ring off?

3. How is a liquid thermometer able to measure the temperature outside when it is summer and winter?

4. Why do telephone wires sag in the summer and are tighter in the winter?

5. Why does a balloon placed in dry ice shrink but when it is removed it returns to its original shape?

No matter what questions you pick, you need to make sure that you are writing in full sentences. These are some words that should be included in your answers:

• particles

• expansion

• contraction

• heat energy

One of your answers should include a drawing. Be creative with your answers! You can make up the identity of the student who submitted their question, you can give your column a headline and can make up a name for your column such as “Ask Andy”, “Angie’s Answers”, “Kevin Knows it All” or “Science with Sarah”.

Alex is trying to get the metal lid off of a jar. Should you tell Alex to put the lid under hot or cold water? Why?

Try to include the words expansion and contraction in your answer!

Make sure you can answer these questions so you know you have a good understanding of the material! Try to answer these questions before moving on to the next lesson:

1. What causes objects to expand? (make sure you use the word particles in your answer)

2. What causes objects to contract? (make sure you use the word particles in your answer)

3. What is one reason why it is important to know about expansion and contraction?

Take the quiz to make sure you are on the right track!