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Question on Newton's first law

  1. Nov 13, 2015 #1
    An object with no resultant force can still be moving at constant velocity. Why? Is it because of its kinetic energy or has it got nothing to do with energy?
  2. jcsd
  3. Nov 13, 2015 #2


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    An object which is moving which also has no net force acting on it continues to move without change in its motion. That's Newton's First Law of Motion.

    If you want to make an object go slower, you must apply some force to it.
    If you want to make an object go faster, you must apply some force to it.
    If you want the motion of the object to stay the same, don't apply any force to it.

    Newton's First Law is not concerned with how the motion of the object started initially, only what happens to the object while it is in motion (or not, as the case may be).
  4. Nov 13, 2015 #3
    In addition to SteamKing's answer: It is because of its momentum but it has also to do with energy. Changing the speed changes momentum and kinetic energy and both require a force.
  5. Nov 16, 2015 #4

    David Lewis

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    Common sense and intuition can be deceptive. In everyday experience a constant force may seem to be needed to keep an object moving. However, Galileo discovered that friction and air resistance were obscuring underlying laws. Galileo is quoted verbatim in Newton's First Law.
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