The First Law of Motion

Isaac Newton’s famous three laws of motion starts with the first law, which is “an object at rest stays at rest and an object in motion stays in motion.” This means that if you roll a ball it will never stop moving, and if the ball is still it will stay still. But balls do stop moving, and if you were to place a ball on a slope it will roll down no matter how still it was before.

What the first law actually means is that the ball won’t stop moving if there are no external forces acting upon it. An external force is almost anything that affects the ball, such as gravity, friction and air resistance. The reason the ball stops moving when you roll it on a flat surface is mostly because of friction, and the reason the ball rolls down the hill is because gravity pulls on it. If you were to throw a ball in space, where there is no friction, air resistance and less gravity, the ball would not stop moving until an external force affects it.