Newton’s First Law of Motion states that when an object is set in motion, it will remain in motion until acted on by an outside force. Theoretically, this could mean you could travel at the same speed forever in one direction, right? The reason we don’t see this happen is because of friction. The force of friction is the resistance to motion that is in the opposite direction of the traveling object. This is why if you roll a ball on the ground it eventually stops. Friction is also the reason you can hold a book, and the reason why you don’t slip when walking! The ground and other solid surfaces can cause friction, called dry friction, but fluids (liquids and gases) like water and air can also cause frictional forces, called fluid friction.
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