Grade 7 Expansion and Contraction Worksheet Answers

Solids Expanding and Contracting in our Daily Lives

1.   Why is it important to place gaps at regular intervals in sidewalks?

In the summer the sidewalk expands and in the winter it contracts. The gaps allow space for the expansion and contraction so the sidewalk doesn’t crack.

2.   Steel bolts used to connect things together are sometime heated and put in place while they are still hot. Why?

When hot, the length of the bolts increases. So when they cool,

they pull together the parts they are fastening.

3.   Concrete and steel expand at almost the same rate. Explain why this is important in the construction of tall buildings.

If they did not expand and contract at the same rate, there would be many cracks in the building and it might fall down.

Gases Expanding and Contracting in our Daily Lives

1.   Explain how a hot air balloon is lifted from the ground.

When the gas particles inside the hot air balloon are heated, they expand and some escape from the bottom of the balloon. This causes there to be fewer air particles inside the balloon then outside the balloon. The less dense hot air will float on more dense cold air so the balloon rises.

c) Once in the air, the burner is turned off and the balloon drifts along with the wind. What will eventually happen to the air inside the balloon?

Cooler air will enter the balloon and the air inside will become more dense. The balloon will begin to go down.

 Liquids Expanding and Contracting in our Daily Lives

1.   A bowl of hot soup was left on the table to cool. After a few minutes, the amount of soup in the bowl appeared to have decreased? Why?

Some of the soup may have evaporated or the soup may have cooled down and there seems to be less soup because the particles become closer together (contract) and become denser.

2.   When manufacturers pack liquids into bottles and jars, they leave a small space at the top before putting on the lids. Why?

The space allows for the liquid to expand without causing the bottle to break.

3.   Mercury expands and contracts faster than alcohol. Which liquids would be better in a thermometer?

Mercury will tell the temperature faster, but it will also contract faster so it will drop more quickly making it harder the read the temperature. Also, mercury is poisonous!