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Work and Energy

  • C8-06 PILE DRIVER

    C8-06
    Illustrates gravitational potential energy converting into kinetic energy converitng into work
    Start a nail into the center of the wood block. Place the block on the floor with the nail up and position the pile driver tube over the block. Hold the iron weight at the top of the tube and release it. The weight will fall to the bottom and pound the nail into the wood.
    C8, OS0

  • C8-11 INTERNAL VS. EXTERNAL ENERGY - SPRING-COUPLED SUPERBALLS

    C8-11
    Shows that when energy disappears from the center of mass motion it may be converted into internal energy
    Hold the balls horizontally with the spring relaxed and drop; it should produce a high rebound. Then drop at an angle of about 45 degrees to the horizontal. The device will not rebound very high, but will develop a lot of internal energy, as evidenced by lots of spring vibration.

    This device can also be used as a simple model of energy in a two-atom molecule. Erik Neumann has created a simulation of this demonstration for this purpose as well. It can be found at https://www.myphysicslab.com/springs/molecule2-en.html .
    C8

  • C8-12: JUMPING MASSES WITH INTERNAL SPRINGS

    C8-12
    Demonstrate conversion of internal energy of a spring into kinetic energy and then gravitational potential energy.
    Set device so as to store energy in the spring by compressing or twisting the spring. Release rapidly or as required to allow conversion of energy stored in the spring into other forms.
    C8

  • C8-13: BUNGEE JUMPER MODEL

    C8-13
    Determine the minimum value of the spring constant of a bungee rope to ensure a safe jump.

    Student of mass M jumps from a cliff of height H tied to a bungee rope of unstretched length Lo. Assume a vertical jump with initial velocity of zero. Neglect air resistance and mass of the rope.

    When the spider jumps off the platform the spring extends to within a few inches (or centimeters in physics) of the floor before pulling the spider back up.

    DANGER - IMPORTANT NOTE: Bungee cords are made of shock cords (elastomers) or from rubber. They DO NOT behave as linear springs. It would be dangerous to assume linearity of a real bungee jumping cord and make calculations on this basis.
    FS1

    c8-13a

  • C8-14 JUMPING CLAMP

    C8-14
    Demonstrates mechanical potential energy transforming into kinetic energy
    The clamp is held open with a string. When the string is burned, the clamp closes rapidly, jumping into the air.
    C8

  • C8-21: ROCK AND WASTE BASKET

    C8-21
    Demonstrate conservation of energy in a humorous way.
    Hold the rock up head high and drop it into the waste basket. Use the board to prevent damage to the floor. Have your students list all the possible types of work and energy involved, such as work done lifting the rock, gravitational potential energy, kinetic energy, heat, sound, and energy of deformation.
    OS1

  • C8-22: ENERGY CONVERSION - SUPERBALL AND SOUNDING BOARD

    C8-22
    Show transformation of energy from one form to another.
    Observe that the rebound of the superball is less when it is dropped on the metal shelving than when it is dropped onto a hard surface such as the floor. Discuss the possible forms of energy involved. Do the same experiment with a ping pong ball; describe and explain any differences.

  • C8-23: WORK DONE BY PUSHING ON WALL

    C8-23
    Illustrates that the wall and the floor do no work.
    The instructor, while standing on a cart weighted with two lead bricks, pushes off against the wall. The energy comes from the pusher, not from the wall or the floor or the air. Be careful. This can be dangerous if you get unbalanced. Of course, this danger to the instructor heightens the interest of the students.

  • C8-31: POWER - EXERCISE CYCLE

    C8-31
    Measure human work.
    Apparatus measures speed, distance, and load. Work output can then be calculated.
    FS1

  • C8-32: POWER - CLIMBING LADDER

    C8-32
    A simple method for illustrating power and the unit of the horsepower.
    Climb the ladder at a constant rate, say one foot per second. From your weight you can then calculate your power, in foot-pounds per second or in horsepower.

  • C8-33: POWER - USING GRAVITY

    C8-33
    Demonstrate mechanical power.

    A one-half kilogram mass provides a force of about 5 Newtons hanging over the pulley. Under the specially selected 5 Newton force the wooden box moves at a nearly constant speed. The distance and time can be measured and the power calculated.

    Add small masses to the wooden box or to the pulley weight to adjust the motion as necessary.
    C8, ME1

  • C8-34: POWER - INSTRUCTOR DRAGGING CONCRETE BLOCK

    C8-34
    Demonstrate power
    Drag block with uniform speed and measure the force. Calculate the power from the force, the distance traveled, and the time elapsed.
    FS1, ME1

    c8-34a

  • D1-62: CONSERVATION OF ENERGY IN ROLLING BODY

    D1-62
    Demonstrate conversion of gravitational potential energy into translational and rotational kinetic energy.
    The spool slowly rolls down the incline on its smaller radius, converting gravitational potential energy into rotational kinetic energy with a lesser amount of translational kinetic energy. When the spool reaches the bottom, the larger radius rims make contact with the table top, resulting in a sudden transfer of some of the rotational kinetic energy into translational kinetic energy.

  • D1-63: MAXWELL PENDULUM - LARGE

    D1-63
    Demonstrate transformations between gravitational potential energy and rotational kinetic energy.
    Used as a large-scale yo-yo, transformation of energy can easily be observed by a large class. Wind the string around the small spool radius, hold with the axis horizontal, and release. The initial gravitational potential energy is converted primarily into rotational kinetic energy, with a lesser amount of translational kinetic energy, as the device moves downward, with conversion back to gravitational potential energy after the spool reaches its minimum position and moves back upward.

  • D1-64: MAXWELL PENDULUM - SMALL

    D1-64
    Demonstrate transformations between gravitational potential energy and rotational kinetic energy.
    Wind the string up on the small axel, giving the device some initial gravitational potential energy. When released, this gravitational potential energy is converted into rotational kinetic energy, with a lesser amount of translational kinetic energy, as the device moves downward, then converted back as it rises. Two different sizes of small axels are available.

  • D1-65: YO-YO

    D1-65
    Illustrate transformation between various forms of energy and to perform yo-yo tricks.
    Simply holding the end of the string to allow the yo-yo to unwind and wind back up again illustrates transformation between gravitational potential energy and rotational kinetic energy, with a lesser amount of translational kinetic energy. See Demonstration Reference File for further information on yo-yo tricks.

  • D3-12: SWING MODEL

    D3-12
    Model the pumping of a swing using conservation of angular momentum.

    A mass (the swing) hangs from a rope that passes over a pulley and is connected to the support post. A second shorter rope hangs freely from the horizontal section of the main rope.

    Start the pendulum mass oscillating with a small amplitude. When the pendulum gets to its lowest position, pull gently down on the shorter rope, shortening the pendulum and thereby increasing its velocity. Release the rope as the pendulum nears its high point.

    According to a possibly oversimplified analysis, conservation of angular momentum at the low point, before and after the pull is applied, explains why this procedure causes the amplitude of the swing to increase with time. See also discussion of parametric resonance.
    D3, FS2

  • D3-32: KEYWHIP

    D3-32
    Demonstrate angular momentum conservation in a surprising way.

    A string about one meter long has a (relatively heavy) set of keys on one end and a (very light) match box on the other end. The string passes over a pencil with the keys hanging down and the matchbox held horizontal to the pencil with about two/thirds of the string between the pencil and the matchbox.

    Q: What will happen when the match box is released?

    A: Surprisingly, the keys will not fall to the floor. When the matchbox falls it develops angular momentum. Conservation of angular momentum of the matchbox causes it to rotate very rapidly about the pencil as the string pulls it in. Before the string is used up, the matchbox string actually wraps around the pencil, preventing the keys from falling onto the floor!

  • D5-23: ROTATING BEAD ON LOOP

    D5-23
    Demonstrate the presence of a "critical parameter" which determines the dynamic behavior of a simple physical system.
    Attach the mounting frame to the variable speed rotator and adjust the rotation rate to less than approximately 1.6 revolutions per second. The bead remains in equilibrium at the bottom of the loop. For rotational rates greater than 1.6 revolutions per second, the bead will be in stable equilibrium at a non-zero angle dependent on the rotation rate. Frictional effects are considerable; nevertheless the presence of a critical angular velocity can be seen.
    D5, D1

  • G3-44: WAVE-DRIVEN BUMPER JACK

    G3-44
    Demonstrate that waves transmit energy.
    Waves are sent along the stretched spring from your hand to the other end, which is attached to the handle of a bumper jack. If you send an appropriate frequency of wave, the energy transmitted to the bumper jack will lift the 7 kg mass, demonstrating that the wave is actually transmitting energy.