The case whereby sound waves are heard at either a higher or lower pitch due to an object's motion is called:
the doppler effect
shock waves
beats
resonance

the Doppler effect

Explanation:

The doppler effect is what we called the effect that happens when the wavelength or frequency of a sound changes because the observer is moving relatevily form the object, could be moving closer or moving further away, but the wavelenght and the frequency changes alongside with the movement.

wire in brush may conduct electricity from cell to drill and vice versa electrc shock possible

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