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A pendulum impact hammer setting objects off on a frictionless surface.

  1. Mar 25, 2012 #1

    I want to design a crude pendulum impact device which i can use to measure initial velocities of objects on a frictionless surface. i.e measure energy at the start and end of the pendulums swing, to see how much has been absorbed into the impact.

    Heres my question about momentum on frictionless surface. Picture the pendulum at its NORMAL position, potential energy is zero, kinetic is maximum, we calculate the velocity of the pendulums hammer using 1/2mv^2. At this point is also when it collides with the object on the flat frictionless surface.
    EDIT(this is obviously after the pendulum has been let go from rest at an angle, an dhas just reached the normal position)
    If the mass of pendulum is equal to the mass of the object on the surface, we would simply have a situation where the pendulum exchanges its velocity into the object on the frictionless surface, and then is at rest.

    Is this true?

    if so then what happens when the mass of the pendulum is LOWER than the mass of the object on the frictionless surface? Does it bounce back in the opposite direction?

    lets say the distance from the center of the pendulum is 0.2m from its pivot.

    The method i am using to calculate the difference in energy from the pendulums wing, is measuring the angle of fall and the angle of rise, to calculate initial potential energy, and final potential energy, to find the amount of energy transferred to kinetic energy in the collision.

    This relies on a "trailblazer" needle that rests at normal, but follows the angle of the pendulum on its motion in the angle of rise.

    I dont want a situation where the pendulum mass bounces back in the direction of its swing. Theroretically this shouldnt happen?

    I always want the mass to swing though a decent angle into the rise tho that it can be measured by the "trailblazer" allowing the person conducting the experiment to calculate energy transfer properly.

    Lets say the lowest mass of the object on the frictionless surface will be 0.3kg. What sort of minimum mass should i have as my pendulum hammer?
    Last edited: Mar 25, 2012
  2. jcsd
  3. Mar 26, 2012 #2


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    Science Advisor

    Right, if the pendulum mass is less than the target, then it will bounce back, assuming an elastic collision. To most efficiently transfer the energy, the pendulum mass should be equal to the target.
  4. Mar 27, 2012 #3
    Ok, thanks for that. How do i show this by theory though? May sound stupid but ive always been dodgy with my understanding of the momentum equations.
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