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Confusion with horizontal component of PROJECTILE MOTION

  1. Sep 3, 2008 #1
    Can anybody answer to me why the horizontal component of a projectile motion has no net force?Why is it move with constant velocity ?

    I know that motion doesnt need force but acceleration need force.

    But at the time a projectile motion started it motion ,why can it doesnt required force to make it move?
    and where does this force go?

    Thanks for answering me.
  2. jcsd
  3. Sep 3, 2008 #2
    You are right, standing or constant-velocity-motion has no net force
    Force is applied to maintain the acceleration. And the constant-velocity-motion has no acceleration then the force applied to it is zero.
    When you are pending to throw a body projectile, its velocity is zero. Hence to let it fly you must put a force F, this force give the body a kinetic energy and this energy causes the motion with velocity v. After throwing, you are no longer apply any force upon the body. But there are another force acting on the body, it's weight. But weight force is only available in vertical component and causing the vertical acceleration. However, there is no force acting on horizontal component and then the horizontal component becomes a constant-velocity-motion
  4. Sep 3, 2008 #3


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    For a projectile, the only forces acting on it are gravity and air resistance. We usually neglect air resistance in physics class problems, so we have just gravity as the only force.

    Gravity acts vertically, so no horizontal force is present.

    I think you are answering your own question here. With no force, there is no acceleration. No acceleration means no change in velocity, by definition of what acceleration is.

    Good question. It does require a force to start it moving. It's often something like a person throwing a ball, and the person is applying the force. After this force stops acting, the object becomes a projectile. The force "goes away" when the person releases the ball.
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