Section 3
Understanding Matter and Energy
A Coin Jump
Discover that heated air expands and can cause movement.
The particle theory of matter states that all water consists of
many small particles that are constantly moving. Temperature
affects the speed at which these particles move. This concept
is also known as thermal expansion. “Thermal” refers to heat
and “expansion” refers to the increase in volume.
Thermal expansion occurs when an object changes its shape,
volume, and/or density due to an increase in temperature.
As temperature increases, particles move faster and take up
more space. This means the volume increases.
But what happens to the pressure of the object? Try this
experiment to find out how pressure changes due to an
increase in temperature.
Pressure-temperature
Relationship of Gases
• same number of gas particles
• same volume
• an increase in temperature
• How does the pressure change?
Popular Book Company (Canada) Ltd. Complete ScienceSmart • Grade 7 1
Section 3
Understanding Matter and Energy
A Coin Jump
Ask an adult for help when
handling hot water.
Try this experiment to examine
how thermal expansion can
cause movement.
Materials:
• 2 bowls • a glass bottle
• ice cubes • hot water
• 1 coin
(slightly bigger than the bottle’s mouth)
Steps:
1. Fill one of the bowls with the ice cubes.
2. Place the glass bottle in the bowl of ice cubes upside down so that its neck is
submerged in the ice.
3. Place the coin inside the bowl of ice.
4. Leave the bottle and coin in the ice for about ten seconds.
5. Fill the other bowl with hot water with the help of an adult.
6. Remove the bottle and coin from the ice. Place the coin on top of the bottle
so it covers the bottle’s mouth.
7. Place the bottle and coin upright coin
in the bowl of hot water.
glass
8. Observe what happens to the coin. bottle
hot water
Popular Book Company (Canada) Ltd. Complete ScienceSmart • Grade 7 2
Section 3
Understanding Matter and Energy
A Coin Jump
As you observed, the coin began to jump up and down after the bottle
was placed in the hot water, and it continued to jump for a while.
At the beginning, the bottle
and the air inside it was cold
because of the ice. As soon as
the bottle was placed in the hot
water, the air particles inside the
bottle rapidly heated up, causing
thermal expansion to occur.
However, the heated air particles
were contained in the bottle with
a fixed volume and did not have
space to expand, so the pressure
inside the bottle increased. The
warm air inside the bottle pushed harder than the cool air outside, so
it pushed its way out of the bottle, causing the coin to jump up and
down. The coin stopped jumping when the air pressure inside the
bottle reduced and became the same as that outside the bottle.
higher pressure
causing the coin
to jump
Popular Book Company (Canada) Ltd. Complete ScienceSmart • Grade 7 3
