Which statement best defines motion?

Which statement best defines motion?

• A. Movement of an object in relation to a fixed point
• B. A force that attracts two bodies
• C. Total energy of a system
• D. Rate of change of velocity

Answer: (A)

Motion is about how an object's position changes over time when you compare it to a reference point. If you pick something fixed as that reference, the object's movement relative to it is motion. The other ideas describe related concepts but not motion itself: a force that attracts two bodies is gravity, which is a force; the total energy of a system is energy, not position; and the rate of change of velocity is acceleration, which tells you how motion is changing but doesn’t define motion. So the movement of an object relative to a fixed point best captures what motion is. For example, a car moving past a tree is motion relative to the tree.

Motion is about how an object's position changes over time when you compare it to a reference point. If you pick something fixed as that reference, the object's movement relative to it is motion. The other ideas describe related concepts but not motion itself: a force that attracts two bodies is gravity, which is a force; the total energy of a system is energy, not position; and the rate of change of velocity is acceleration, which tells you how motion is changing but doesn’t define motion. So the movement of an object relative to a fixed point best captures what motion is. For example, a car moving past a tree is motion relative to the tree.