Periodicity
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Waves propagate or move through a medium which is typically a fluid like water or a gas like air.
Waves can also propagate through solid material.
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If you hit a piece of metal so that it starts ringing, the ringing is the effect of waves propagating through the solid metal.
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As the metal vibrates, it causes the air to vibrate, creating sound waves which propagate through the air to your ear.
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Waves of all types have periodically repeating properties
The repetition can be in physical space, or in time, or both
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For waves like sound and water, repetition is in both dimensions
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Electromagnetic waves (radio, TV, light, X-rays, microwaves etc.) operate in physical space as well as the electric and magnetic field spaces. Generally all three are measured by distance.
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