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Outcomes
Outcomes
Describe expansion in terms of the particle model.
Describe contraction in terms of the particle model.
Explain that gases under high pressure have an increased frequency of particle collision. (Optional)
Explain that gases under low pressure have a decreased frequency of particle collision. (Optional)
Expansion and contraction
Expansion and contraction
Substances expand (increase in size) when they get warmer, and they contract (decrease in size) when they get cooler. This property can be useful. For example:
Thermometers work because the liquid inside them expands and rises up the tube when it gets hotter.
Metal parts can be fitted together without welding, using shrink fitting.
The expansion and contraction of materials can also cause problems. For example, bridges expand in the summer heat and need special joints to stop them bending out of shape.
What do the particles do?
What do the particles do?
When substances expand or contract, their particles stay the same size. It is the space between the particles that changes:
the particles in a solid vibrate more when it is heated, and take up more room
the particles in a liquid move around each other more when it is heated, and take up more room
the particles in a gas move more quickly in all directions when it is heated, and take up more room
True and False
Temperature is a measure of how hot or cold something is.
The greater the number of degrees measured by a thermometer, the lower the temperature.
Heat energy moves from hot to cold.
Hot objects have more heat energy than cold objects.
The molecules in an object move slower when the object is cold.
EXTENSION: Particle collision theory
EXTENSION: Particle collision theory
1. What is collision theory?
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