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Linear Momentum

  • C7-01: AIR TRACK - ELASTIC COLLISIONS

    C7-01
    Demonstrate conservation of energy and conservation of momentum in elastic collisions.
    Air track gliders on a frictionless track are used to illustrate elastic collisions. A photocell gate timer is used to measure the time taken by a 5 cm tab on the glider to pass through the photocell gate and thus to obtain the velocity of the gliders. To obtain more than one timer reading the gates must be positioned carefully and the timer reset between readings using the cable-mounted reset switch.

    Compare the real experiment to this similarly designed simulation by Erik Neumann at MyPhysicsLab. The simulation lets you adjust the mass of the "carts," the stiffness of the springs, and other variables.

  • C7-02: AIR TRACK -INELASTIC COLLISIONS

    C7-02
    Demonstrate conservation of momentum in elastic collisions.
    Air track gliders on a frictionless track are used to illustrate inelastic collisions. A photocell gate timer is used to measure the time taken by a 5 cm tab on the glider to pass through the photocell gate and thus to obtain the velocity of the glider. To obtain more than one timer reading the gates must be positioned carefully and the timer reset between readings using the cable-mounted reset switch. Use pairs of masses which have opposite sex of velcro for inelastic collisions. The mass with the tab is pushed through the first gate to commence the collision.

  • C7-03: AIR TRACK - SCATTERING WITHOUT CONTACT

    C7-03
    Show that elastic scattering can occur between two objects without actual physical contact between the objects.
    Magnets with the same polarity mounted on air track gliders provide the repulsive force between the two gliders without actual physical contact. Elastic scattering between these two gliders proceeds in exactly the same way as when they contact through the bumper springs. The photograph at the bottom is a close-up of the magnets mounted on the ends of the gliders.

  • C7-04: AIR TRACK - COLLISION VELOCITY MULTIPLIER

    C7-04
    Illustrate velocity multiplication with a three-to-one mass ratio collision.
    Air track gliders with masses in the ratio of three to one, moving with the same speed, collide with the end of the air track (at right side of photo). After the collision sequence, the larger glider remains at rest while the smaller glider leaves with twice its initial speed, thus carrying away the total kinetic energy of both gliders before the collision.

  • C7-11: COLLISIONS OF BALLS - EQUAL MASSES

    C7-11
    Demonstrates conservation of energy and conservation of linear momentum in multiple elastic collisions
    Hold one, two, three, or four balls to the side and release. Symmetric oscillations result from conservation of energy and conservation of linear momentum in the collision sequence.

    Click here to go to a simulation of this device by Erik Neumann.
    C7

  • C7-12: COLLISION OF BALLS - ONE LIGHTER MASS

    C7-12
    Show what happens when one mass in a collision ball set is different from the others.
    The collision ball sets photographed are identical except that the fourth ball from the left in the set on top is lighter - the original steel ball has been replaced by one made of aluminum (It is slightly less shiny.). Q: Will the set with one lighter ball work the same as the "normal" set if one ball is picked up and released? A: No. Momentum and energy are transferred in a series of elastic collisions between two balls at a time; for identical balls all the momentum and energy are transferred from one ball to the next in each collision. The lighter mass ball breaks the chain, at which point there is no longer complete transfer of all the energy and momentum to the next ball.
    C7

  • C7-13: COLLISIONS OF BALLS - GRADUATED MASSES

    C7-13
    Demonstrate how the velocity is multiplied by a sequence of collisions between balls of decreasing mass.
    A ball of mass M moving with velocity V strikes a ball of mass m (less than M) initially at rest. For an elastic collision the velocity v with which the lighter ball leaves the scene will be v = 2VM/(M+m). This device has a series of balls, with masses in the same geometric ratio, to provide a velocity multiplication of about 16 from the biggest to the smallest. Click your mouse on the photograph to see a slow-motion video of the action.
    C7

  • C7-14: COLLISIONS OF BALLS WITH FLOOR

    C7-14
    Illustrate collisions of different balls with the floor.
    Drop the four balls simultaneously. They rebound to heights dependent upon the elasticity of the collisions with the floor.
    C7

  • C7-15 COLLISIONS OF BALLS - 3 TO 1 MASS RATIO

    C7-15
    Shows velocity multiplication in colliding balls
    The heavier ball, with mass of three times that of the lighter ball, is held touching and directly under the lighter ball. When the balls are released they strike the floor in a series of almost elastic collisions which transfers all the energy to the lighter ball.
    FS2

  • C7-16: HAPPY AND UNHAPPY BALLS

    C7-16
    Illustrate coefficient of restitution.
    Drop the two balls simultaneously from the same height. One bounces back to almost the original height, while the other stops dead on impact. Which one is happy and which one is unhappy? The happy ball is made from neoprene rubber; the unhappy ball is made from norbornene, a polymer synthesized from ethylene cyclopentadiene.
    C7

  • C7-17 SUPERBALL

    C7-17
    Illustrates nearly elastic collisions
    Drop the superball and watch it bounce
    C7

  • C7-18 COLLISIONS OF BALLS - ASTROBLASTER

    C7-18
    Shows velocity multiplication in colliding balls

    This device has four balls of graduated masses on a central shaft. The smallest has a slightly larger opening so that it can come off the shaft, while the others are trapped in place. If the whole assembly is dropped from 50cm or so about the table, the smallest ball on the end will fly off with considerable velocity, potentially rising to significantly greater than the initial height.

    Please be careful not to lose the small ball, and do not launch it into the audience or at anything else breakable.

    Engagement Suggestion
    • When presenting this device, describe it clearly, then encourage students to predict what will happen when you drop it.
    • Afterwards, have them discuss the results.
    Background

    The total energy of the system, of course, cannot increase beyond what it gains from the potential energy of the height from which it is dropped. But the elastic collisions of each ball with a successively smaller and less massive one transfer significant kinetic energy. With the smaller mass of the final ball, it can have a higher velocity than the collection as a whole did.

    C7

  • C7-19: GAUSSIAN GUN

    C7-19
    Demonstrate transfer of energy in an elastic collision
    Ball bearings in a track are accelerated by a magnetic field, showing a collision where momentum appears to not be conserved.

    Compare to K2-40: Magnetic Accelerator
    OS0

  • C7-21: ENERGY AND MOMENTUM - COLLISION AND PROJECTILE

    C7-21
    Illustrate conservation of momentum and conservation of energy.
    A pool ball, suspended as a pendulum of length L, is released from an angle a and collides with an identical pool ball initially at rest. The second pool ball then immediately projects horizontally off the edge of the lecture table of height H. The range R of the projected ball is given by R = 2 SQRT [ LH (1 - cos a)]
    C7

  • C7-23: MEDICINE BALL AND SKATEBOARD

    C7-23
    Demonstrate large-scale collisions
    Throw medicine ball to student sitting on skateboard. Student sitting on skateboard can throw medicine ball off.

  • C7-25: SUPERBALL, VACUUM MUD AND WOOD BLOCK COLLISIONS

    C7-25
    Show that a larger impulse is imparted by an elastic collision.
    A vacuum mud ball at the end of a rod is held horizontally and released so that it swings into a wooden block. The vacuum mud ball is replaced by a superball with the same mass, and the experiment repeated. Q: In which of these cases will the wood block be knocked over? A: The superball knocks over the wooden block because it bounces back, imparting more momentum to the block.
    C7, FS2

  • C7-26: BOUNCING PUTTY AND NON-BOUNCING SUPERBALL

    C7-26
    Show unusual collisions.
    A superball dropped into a container of sand will not bounce. Conversely, a ball of putty dropped onto a foam rubber pad will bounce nicely.

  • C7-42: AIR TABLE - COLLISIONS OF PUCKS

    C7-42
    Qualitatively demonstrate elastic and inelastic two-dimensional collisions.
    Two or more pucks can be used to demonstrate elastic collisions. Velcro collars on pucks (front row of second picture) produce perfectly inelastic collisions. The air table is only available in rooms 1410, 1412, and 0405 because it will not fit through a standard single door. In smaller rooms, please consider C7-43 or C7-44.

    Also see a simulation of similar collisions here: https://www.myphysicslab.com/engine2D/billiards-en.html

  • C7-43: AIR TABLE - SMALL - COLLISIONS OF PUCKS

    C7-43
    Demonstrate collisions of pucks on an air table in rooms not accessible by the large air table.
    This small air table can be readily moved on a small rolling cart into all physics classrooms. Both elastic and inelastic collisions can be demonstrated using a variety of puck masses. Velcro collars are used to create inelastic collisions.

    Also see a simulation of similar collisions here: https://www.myphysicslab.com/engine2D/billiards-en.html

    OS10

  • C7-44: COLLISIONS - HOVERPUCKS

    C7-44
    Demonstrate two-dimensional collisions.
    Two battery-powered hoverpucks, as shown. Can be used to demonstrate a variety of two-dimensional collisions and motion. Velcro collars are available for inelastic collisions.

    Also see a simulation of similar collisions here: https://www.myphysicslab.com/engine2D/billiards-en.html

    C7