Question

One of Newton’s laws of motion states that objects in motion tend to stay in motion. What is the reason that this law may not always prove true for objects on Earth?

Answer 1

The answer is D.

The full specification of Newton's First Law is (from Wikipedia)

In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.

On earth we're generally in slightly a non-inertial frame, with rotation and revolution around the sun. It's also impossible to turn of gravity, so objects are being acted upon by an outside force. Typically there's also the outside force of friction, which makes things tend to stop.

Answer 2

D. The conditions on Earth are different than the conditions specified in the law.

Explanation:

Newton´s law states that an object in motion tends to stay in motion, but this is only true if there are no other forces that will make the object change its direction and speed.

On earth, we have gravity, air and other forces that will make this law not true on Earth all the time.

For example, in space, if there is no other planet close an object will keep moving until it hits something that makes it change direction or speed, or stops it.