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Few Basic Physics Question

  1. Jun 30, 2011 #1

    I have a few questions:

    1) If a rigid object was dropped (and its mass, initial height are known) what would the shape of the Force-time diagram look like and how to find the maximum force?

    2) If an elastic object was dropped knowing only initial conditions is it possible to predict its deformation and whether it will bounce or not?

    3) Why is fictitious centrifugal force outwards of the curve when its velocity/inertia that causes the centrifugal force is tangential to the curve? Also for a circular path how to calculate this force?

    4) How does a damper work, and how does a car suspension facilitate weight transfer?

  2. jcsd
  3. Jun 30, 2011 #2
    on #1 there would be no force until it hit the ground . Just like when you are in free-fall you wont feel your weight. The force when it hit the ground woul be F=dp/dt.
    The change in momentum divided by the impact time. The impact time would be pretty small.
  4. Jun 30, 2011 #3
    1) I assume you mean the impulse force from collision with the ground? I think in theory, the impulse force is usually modeled like some sort of Gaussian function, might also have something to do with the shape of the rigid object. in which case, if you knew something about the function, you could calculate the time at which the derivative was zero, plug that time in and get a max, but that would be difficult to do and not very practical. Direct measurement of force and momentum change would probably be easier.

    2) theoretically you could predict this, but you'd need to know a lot about the object's physical composition.

    3) The centrifugal force is opposite the centripetal force, which points directly inward towards the center of rotation. You can think of the centripetal force and centrifugal force as a newtonian force pair. Imagine being in a spinning, circular room and you're pressed against the wall. That force from the wall is the centripetal force, but within the rotating reference frame, you only perceive it to be an equal and opposite reaction force to some invisible force acting directly outward from the circle. So, it does have to do with momentum/inertia, but it's also directly connected to the centripetal force.

    4) A damper is simply a type of friction on an oscillating system that causes the oscillation amplitude to lessen over time, like a spring, if you load the spring, it will start to oscillate, but for different reasons, both external and internal, it wont spring back and forth forever, it gets damped and eventually stops. And I have no idea how car suspension works, but it would be connected to damping, because a suspension system without proper damping can make for an uncomfortable ride (too bouncy or too rigid).
  5. Jun 30, 2011 #4
    1) The force acting on a freely falling body is the gravitational force which is equal to mg , which alwyas acts towards earth.
    This is the only force acts on it unless an external forces are applied.
    Since the force acting on the dropped object is constant throughout its motion , the shape of the force time diagram is a straight line parallel to the x-axis.

    2) The bouncing of the elastic body depends on the coefficient of elasticity.

    3) centrifugal force can be calculated using the formula

    F = mv^2 /r

    where m is the mass of the object
    r is the radius of the circular path
    v is the velocity of the object.
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