In this lab you will calculate velocities, momenta, and kinetic energies to determine to what extent these quantities are conserved. [br]Principles: If no net external force works on a body (or a system of bodies), then that body’s momentum is constant – it does not change. In this instance, we say that the momentum is conserved. We refer to this as the law of conservation of momentum. [br]The momentum of an individual object may change, but the total for the system does not. Suppose that object 1 is moving with an initial velocity v1i, and collides with object 2, which is moving with an initial velocity v2i: the total momentum of the system BEFORE the collision is then [br]Pbefore = m1v1i + m2v2i [br]AFTER the collision, the objects will likely have new velocities v1f and v2f. [br]The total momentum after the collision is then [br]p after = m1v1f + m2v2f [br]If there is no net external force on the system, then [br]pbefore = pafter[br]Your job in this lab is to see if this equation holds true.[br]Another quantity often looked at in collisions is kinetic energy. The kinetic energy of a body is one-half the product of the mass and the square of the velocity:[br]KE = ½ mv2[br]Kinetic energy, unlike momentum, is a scalar quantity, and always positive. And the kinetic energy of a system of bodies equals the sum of all the individual kinetic energies.[br][br]A collision in which the total kinetic energy is constant before and after the collision is called a perfectly elastic or completely elastic collision. Such, of course, do not exist in the real world.

Procedure[br][list][br][*]Set the masses of the two balls to be equal (0.5 kg is a good value).[/list] [br][list][br][*]Set the length of pendulum to 2m[br][/list][br][list][br][*]Set the h1 of ball2 (red) at 2 m.[br][/list][br][list][br][*]Run the collision and note the velocities of each ball before and after the collision.[br][/list] [br][list][br][*]Record these values on the data sheet. (Note that the subscript i means initial, or before the collision, and subscript f means final, or after the collision.) [br][/list][br][list][br][*]Reset the applet and change the mass of the red ball to 1kg. [br]Repeat the collision and record the velocities. [br][/list][br][list][br][*]Reset the applet. [br]Set the red ball to 0.1 kg and and the mass of green ball to 1kg. [br]Repeat the collision and record the masses and velocities.[br][/list] [br][list][br][*]Repeat the experiment changing the values of m1, m2, l and h1 at your choice.[br][/list]