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Force on moving object

  1. Dec 8, 2005 #1
    could anyone tell me What will happen if a force is acting on moving object at angle theta ( assume theata is niether 90 nor 180)?
  2. jcsd
  3. Dec 8, 2005 #2

    Doc Al

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    Staff: Mentor

    If a net force acts on an object, the object will be accelerated in the direction of the force according to Newton's 2nd law.
  4. Dec 8, 2005 #3
    Acceleration or retardation depend on the angle( you can make component of force along the motion and perpendicular to the motion ).........I wanted to know the trajectory of the moving object ...will it start circular motion around the force?
  5. Dec 8, 2005 #4
    if it is a constant force and is not changing in magnitude or direction, you will just have straight line motion in the direction of the force assuming your object was initially at rest. If you get rid of any of the assumptions in my previous statement then weirder things can happen.

    EDIT: Just noticed that you said a moving object, then what will happen will depend on the initial movement of the object. You will need to decompose your force into a component along the motion of the object and into components orthogonal to this direction. Then the component of the force along the motion of the object will serve to change its velocity in that direction and all the other components of the force will serve to change the direction of the motion, assuming these components are nonzero.
    Last edited: Dec 8, 2005
  6. Dec 8, 2005 #5
    Yes that is what i wanted to know....suppose one force is action along the line ( either accelerating or retarding the object) and the other one is perpendicular ...will try to make the object rotate around it.....but that force should be equal to the cntripital force......will object go on spiral path and finally will it start moving cicularly?
  7. Dec 8, 2005 #6
    if the second force is perpendicular to a force in the direction of motion, like you said the one in direction of motion will accelerate or retard. The other force will just change the direction, you can not get circular motion unless that force is allowed to vary its direction after some time.

    consider this, say you have a particle moving along the x axis, you get a force in +x and a force in +y direction. The +x will make the particle move faster and faster away from the origin in the x-direction. The +y force will start the particle in upward motion away from the x-axis. To get circular motion, you would need this force to then start pushing it back along the x-axis, then down the y-axis, etc. So, if the forces are constant no way to get circular motion, if you let the forces change with time, then you can get some circle/ellipse/spiral type motion.
  8. Dec 8, 2005 #7
    thanks for making the point ....actaully I am sorry I didn't mention forces are not constant...it is a gravitational force ...so inversely proportional to r^2.....what is your opinion now?....suupose it starts retarding the object at t= 0 .....and at that time gravitational force is much weaker than the centripital force ( velocity is higher)....??
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