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science tells us that light bends

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towards air that is more dense

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when looking towards the horizon this

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generally bends the light down because

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air is less dense as you get higher it

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has large changes in temperature than

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this can change things low cold air

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bends the light down more low warm air

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will bend the light upwards

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sometimes creating mirages but how can

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you demonstrate these effects for

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yourself it's actually easy to do with

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common items take a laser pointer and

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bounce it off a mirror the other end of

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the longest room you have this makes the

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position of the doc very sensitive to

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small bends at the start of the laser

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beam then take a flame and put it next

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to the laser heating up the air makes it

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expand which makes it less dense so the

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laser bends away from it and towards the

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cooler air further from the flame for

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cold air take a large ice pack or even a

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tray of ice cubes and position it under

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the beam this calls the air directly

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above the ice making it more dense and

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so bends have beam downwards towards the

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cold dense air what about changes in

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pressure

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I took a plywood board and slammed it

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down onto the beam this compresses the

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air ahead of the board making it more

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dense so you'd expect the first movement

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of the beam to be upwards this is hard

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to see in this shot but it is measurable

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if we were repeated in slow motion this

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initial movement becomes more obvious up

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towards the wave of higher pressure more