4. explain what must happen to an object in order for it to accelerate.

Newton's second law proves that a constant force is acted on a huge body and it causes to accelerate the change and its velocity and at a 'constant rate'.

Explanation:

The application of the force of an object may causes to accelerate in the 'direction of the force'. The object is in motion from a moving inertial reference frame, then the body may appear to speed up and slow down and it change the direction depending on the direction of the force. The direction of the object and reference frame are moving relatively each other.

The force due to the gravitational acceleration a force is exerted on earth and it acts on bodies on the earth. 'Acceleration' is a change of velocity of a body with the time. An object's acceleration it results of all forces they act on the object by the Newton's Second Law.

the  frequency of a wave represents  the number of wavelengths that pass a specific point per second. the unit for  frequency  is hertz (hz).

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