Follow

Work and Energy

  • B3-12 PULLEY - MECHANICAL ADVANTAGE

    B3-12
    Illustrate pulley systems
    The system is initially balanced to account for the weight of the pulleys and rope by adding small weights on the free end of the rope, as seen in the photograph at the left. For every two kilograms hanging from the pulley, the system requires one kilogram hanging from the free end of the rope to obtain equilibrium. Show that deviation from the 2:1 ratio destroys the static equilibrium.
    FS1

  • B3-14: EQUILIBRIUM PARADOX - SCALES AND PULLEY

    B3-14
    Counterintuitive demonstration involving pulley system
    A frame containing the pulley and the lower scale hangs from the upper scale as photographed. The initial weight of the lower scale, pulley, and frame together is about 5 Newtons, as read on the upper scale; initially the lower scale reads zero. The difference in resultant force due to the pulley can be observed from the difference in the change of the two scales.
    FS2

     

  • B3-21: CHISEL AS WEDGE

    B3-21
    Demonstrate the mechanical advantage of a wedge

    A wedge is used to split a piece of wood.

    For your safety, goggles are provided
    B3

  • B3-23: Worm Gear

    B3-23
    Illustrate mechanical advantage
    The worm gear is a simple machine which illustrates mechanical advantage. Using only a small torque, a relatively heavy weight can be lifted. Concomitantly, a fast rotation of the worm produces a slow angular displacement of the wheel. The mechanical advantage is 136.
    B3, FS2

  • C2-11 RACING BALLS

    C2-11
    Illustrate linear kinematics

    Two balls are launched by a spring-operated launcher from one end of the track. They depart with the same velocities and the same kinetic energy imparted by the spring. As shown in the picture, one track runs in a straight line; the other dips down, runs straight for a time, then rises back up to the original level.
    Engagement Suggestion:
    Have students make predictions (and justify them):
    • Which ball will reach the end first, or if they will reach the end at the same time?
    • Which one (if either) will be moving faster at the end?
    Background:

    The ball on the straight track retains essentially the same velocity and the same kinetic energy throughout the length of its run, the kinetic energy from the spring. The ball on the dipped track, however, has a more complex path. When it goes downhill, it gains kinetic energy from gravitational potential, accelerating it. It travels along the lower section of track with this increased kinetic energy, and thus greater velocity. The ball then goes uphill again, losing that additional kinetic energy – it has returned to the same height, so the principle of conservation of energy dictates that it must return to the same gravitational potential as before, giving up kinetic energy equal to what it gained. It now has only the same kinetic energy it started with, as imparted by the spring. So its velocity is now the same as its starting velocity, and the same as the velocity of the other ball.

    However, during the time it was on the lowered section track, it had greater kinetic energy and greater velocity, so it traveled that distance faster than the ball on the straight track. And thus the ball on the dipped track reaches the end first, but with the same final velocity and the same final kinetic energy.
    OS0

  • C4-21 ATWOOD MACHINE

    C4-21
    Illustrate the second law of motion. Experimentally determine the acceleration due to gravity.

    This classic demonstration illustrates motion under the acceleration of gravity. When used carefully, approximate measurements can be made.

    Equal masses M of 200 grams are hung on the ends of a light string passing over a light, frictionless pulley. When an additional mass of 100g is hung on one end, the resulting acceleration can be measured by timing the motion of either mass over a distance S between two points. The acceleration of gravity g can then be calculated: g = a (2M + m)/m, where a is the acceleration of the system: a = 2S /t^2.
    C4, FS2, ME1

  • C4-22: HORIZONTAL ATWOOD MACHINE

    C4-22
    Demonstrate the Horizontal Atwood Machine quantitatively.
    A mass m connected to a string passes over a pulley and is attached to the Horizontal Atwood Machine, of mass M, as photographed. When the system is released, and begins to accelerate, the tension in the string is reduced, as can be read from the spring scale. The tension T in the string while the system is accelerating can be calculated and compared with the tension observed on the scale: T = Mmg/(M+m), or T/g = Mm/(M+m) in mass units indicated by the scale mounted on the cart. In this case M=875g and m=200g, so the scale reads 200g (photograph above) when the system is held at rest and 163g (previous mark on scale is 150g) shortly after it is released. This can be seen in a half-speed mpeg video by clicking the link below.

  • C4-23: ATWOOD MACHINE WITH HEAVY PULLEY

    C4-23
    Illustrate the affect of a heavy pulley on the Atwood Machine.
    Two Atwood Machines, both having the same hanging masses, are mounted on a stand. One is an "ideal" device, in that it has a very light pulley, while the other one has a massive pulley with a concomitant large moment of inertia. Motion of the two systems can be compared and discussed.
    C4, FS2, ME1

  • 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.

  • C7-03: 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.

  • C7-17 SUPERBALL

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

  • C7-26: 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.

  • C7-52: BALLISTIC PENDULUM - LABORATORY MODEL

    C7-52
    Demonstrate operation of the standard laboratory type ballistic pendulum.
    A heavy ball is placed on the compressed spring, as shown in the photograph, and released by pulling the trigger. The ball fires into a catch on the bob of a physical pendulum, causing the bob to swing to a large angle, where it is caught by a ratchet system. Due to lack of time, this device is generally demonstrated only qualitatively during regular class lectures.
    OS1

  • C7-53: AIR TRACK - SPEED OF AIR GUN PELLET

    C7-53
    Determine the speed of an air gun pellet using conservation of momentum in an inelastic collision.
    The pellet is shot into a receptacle mounted on an air track glider. Conservation of momentum in the ensuing totally inelastic collision allows determination of the velocity v with which the pellet was shot: v = [(M+m)/m] V, where m is the mass of the pellet, M is the mass of the glider/receptacle, and V is the measured velocity with which the glider leaves the collision. The speed of the glider is determined using a photocell gate timer. Compare this result with the result from the standard ballistic pendulum demonstration using the air gun pellet, Demonstration C7-51. Pump the gun once only. Be familiar with the safety mechanism, and know where the pellet exits the gun before firing.

  • C8-01: GIANT PENDULUM

    C8-01
    Demonstrates conservation of energy
    The instructor backs up against the ladder/plywood backdrop, holds the pendulum bob up to his or her chin, and releases it. Because of conservation of energy the bob will swing across the stage and return to its original position adjacent to the instructor's chin, but without hitting his or her chin. Despite the wariness of the students, the pendulum bob cannot rise to a height greater than its original height, and the instructor is safe. Demo requires a minimum of 24 hours notice to prepare mounting cable. E-mail Lecture-Demonstration the day before to ensure that cable is ready.
    C8, OS11

  • C8-03: GALILEO'S PENDULUM

    C8-03
    Demonstrate conservation of energy in a simple system.
    The pendulum is hung from the upper peg with the lower peg interrupting its swing to the right. When started from the left at a given height, the pendulum rises to that same height on the right, after being stopped by the lower peg.

    See demonstration G1-20 to explore more complexities of this setup.
    FS2

  • C8-04 HILL TRACK

    C8-04
    Demonstrates conservation of energy
    A ball is placed at some point on the left side of the track and released. The motion of the ball down the track and over the hill can be described in terms of gravitational potential energy and kinetic energy. The ball must be released at some minimum height in order to pass over the hill.
    OS0

  • C8-05: CONSERVATION OF ENERGY IN VERTICAL PROJECTILE

    C8-05
    Show the relation between initial velocity and height of a vertical projectile.
    A projectile is launched vertically. The laser and photocell timer setup is used to determine the initial upward velocity of the projectile. The height is measured using the scale behind the projection device. The measured height h and the measured velocity v are related by the equation v**2 = 2 gh, where g is the acceleration of gravity. Result is good to better than ten percent.
    C8, LS1, ME1