Newton's First Law So how exactly does a force relate to motion? Intuitively, we can say that a force, at least in some way, causes motion. When I kick a ball, it moves. Newton makes this relation more precise in his first law: An object moves with constant velocity unless acted upon by a net external force. What does this mean? Let's start by looking at a special case where the constant velocity is zero, i.e. the object is simply at rest. Newton's First Law states that the object will stay at rest unless a force acts upon it. This makes sense: the soccer ball isn't going anywhere unless someone kicks it. This concept is true not only for v = 0 , but for any constant velocity. Consider now a ball rolling with a constant velocity. Neglecting friction, the ball will continue to roll with the same velocity until it hits something, or someone kicks it. In physics terminology, it will keep the same velocity until acted upon by a net external force. What does Newton mean by a
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