Heat

When particles gain thermal energy they vibrate more.  As a result they spread out making the spaces between the particles bigger.  This means that the object as a whole expands. In this case the ball no longer fits through the ring. In solids this is called conduction.

 

In liquids the same thing happens. the hot particles spread out as they gain thermal energy but as the particles can move around in the liquid the hot particles rise through the colder liquid setting up a convection current.

This works for gases as well as liquids and solids.  As the particles spread out the gas becomes less dense so gives greater lifting power. A hot air balloon works on this principle using only the temperature difference of the hot air in the balloon and the colder air around it to lift its passengers into the air.

The opposite is also true. A balloon stays inflated because the particles of the gas inside the balloon have great enough energy to stretch the rubber as they are banging against the inside. If the particles are cooled down they no longer vibrate as much and move closer together as they have lost energy. Liquid nitrogen is one way of doing this.

This final video reviews the types of thermal energy transfer we have covered in this page.

 

 

 

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