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Direction of force

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  1. Apr 13, 2016 #1
    1. The problem statement, all variables and given/known data

    My teacher said that if you are holding an object in your hands and lowering it downwards, you are applying force in the upwards direction. How does this make sense and are there any other cases where the direction of an objects force is opposite the direction of its motion?
    2. Relevant equations
    --

    3. The attempt at a solution
    Does this only happen when an object is slowing down in one direction- slowing down in one direction, the force applied on the object is in the opposite direction?
     
  2. jcsd
  3. Apr 13, 2016 #2

    Simon Bridge

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    The net force gives the acceleration, not the velocity.
    An example is if you are in a car and applying the breaks... your motion is forward but the force is backwards.
    If the car goes forward around a circle at constant speed, then the force points towards the center of the circle.

    In your example, though, your hands are not the only force on the object, there is also gravity.
    Your hands are making the object fall more slowly that it would under gravity alone, so you are reducing the total downward force the object experiences... so you must be providing an upwards force.

    It is possible to have many forces on an object that do not point in the same direction as the resulting acceleration... this is unremarkable because it is the net force that determines the acceleration. The object may be picking up speed in the direction opposite the force... that just means there is another, even stronger, force present.
     
  4. Apr 27, 2016 #3
    Thank you
     
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