1/4/2023 0 Comments First law of motion![]() ![]() ![]() Additionally, if we know enough about the friction, we can accurately predict how quickly the object will slow down. However, when the air is turned on, it creates a nearly frictionless surface, and the puck glides long distances without slowing down. When the air is turned off, the puck slides only a short distance before friction slows it to a stop. The object would not slow down at all if friction were completely eliminated. Friction is thus the cause of the slowing (consistent with Newton’s first law). Extrapolating to a frictionless surface, we can imagine the object sliding in a straight line indefinitely. If we make the surface even smoother by rubbing lubricating oil on it, the object slides farther yet. If we spray the surface with talcum powder to make the surface smoother, the object slides farther. ![]() For example, consider what happens to an object sliding along a rough horizontal surface. The idea of cause and effect is crucial in accurately describing what happens in various situations. If friction disappeared, would the object still slow down? An object sliding across a table or floor slows down due to the net force of friction acting on the object. We will define net external force in the next section. Rather than contradicting our experience, Newton’s first law of motion states that there must be a cause (which is a net external force) for there to be any change in velocity (either a change in magnitude or direction). Note the repeated use of the verb “remains.” We can think of this law as preserving the status quo of motion. A body at rest remains at rest, or, if in motion, remains in motion at a constant velocity unless acted on by a net external force. ![]()
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