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PHYS121

  • C5-18 FAN CART

    C5-18
    Demonstrate Newton's third law of motion
    This small wheeled cart has a battery-powered fan mounted on it, and a slot at the end that can hold a plastic sail. With the sail off, turning on the fan drives the cart in the direction opposite the blowing air. With the sail on and the fan off, blowing on the sail will drive it in the direction you blow. With the sail on and the fan on, the sail visibly flexes, but the cart goes nowhere at all. The force acting on the sail is such that it exactly cancels.

    Note: The fan spins quite fast. Don't let it hit your fingers! To connect and disconnect power, use the alligator clip wire on the rear; clip it to the fan support frame for safety when not in use.

    Consider inviting students to make predictions about the cart's behaviour with and without the sail. Invite them to discuss the forces involved.
    C5

  • C6-01 INCLINED PLANE - FRICTION BOX AND WEIGHTS

    C6-01
    Shows that the coefficient of friction does not depend upon the mass of the object although the frictional force does.

    A box sits on an adjustable inclined plane. Masses can be placed in the box to change its weight, and thus the normal force exerted by the inclined plane.

    Set the empty box on the incline and increase the angle until sliding ensues. Add weights to the box and repeat the experiment. The weighted box begins to slide at the same angle.

    (Optionally, a string and pulley can be used to add add an additional force to the system.)

    C6, ME1

  • C6-11: SLIDING FRICTION - LECTURE TABLE AND FELT

    C6-11
    Show the effect on frictional force of velocity, normal force, and contact area.
    The spring scale is connected by the rope to the friction block, which has one of its foam rubber-covered sides contacting the table. Pull with the rope parallel to the table so that the spring scale is visible to the class. Several features of frictional force are demonstrated as follows: (1) Static versus sliding friction, by slowly increasing the pulling force until the block begins to move. The force required to keep the block moving at a constant slow velocity is less than the force required to break the static friction and start the block in motion. (2) The frictional force doubles when a second block of equal mass is placed on the sliding block. (3) The frictional force is approximately independent of contact area, which can be demonstrated by turning the block so that it rests on the narrow felt surface and repeating experiment 1.
    C6

    c6-11a

    c6-11b

  • 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.

  • C7-11: 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

  • C7-13: 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

  • C7-16: 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

  • 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

  • C8-06 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

  • C8-13: 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

  • C8-32: 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.

  • C8-34: 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

  • D1-32: TRAJECTORY FROM CIRCULAR ORBIT

    D1-32
    Show that the instantaneous velocity of an object executing uniform circular motion is tangent to the circle.
    A pool ball is rolled clockwise around the inside of the circular band. When the ball leaves the end of the circular segment it will travel in the direction tangent to the circle at the point where it leaves. Consider placing tape markers on the table or floor and having students predict which direction it will go before performing the experiment. Have them justify their conclusions, then discuss the results afterwards.

    Compare D1-30 and D1-32, which show similar effects.
    D1

  • D1-33 ROTATING MASS ON STRING

    D1-33
    Illustrates centripetal force and that instantaenous velocity is tangent to the circular path
    Swinging the ball around one's head demonstrates uniform circular motion. If the string is released, its initial trajectory is tangent to the circular path
    D1

  • D1-34 ROTATING MASS ON SPRING

    D1-34
    Illustrates centripetal force
    Swinging the ball around one's head will cause the spring to extend, indicating the spring is under tension -- the centripetal force on the ball. By rotating the ball faster, the spring will extend more
    D1

  • D1-35 CENTRIPETAL FORCE - ROTATING MASS

    D1-35
    Measures the required centripetal force for an object to move with uniform circular motion
    A one-kilogram mass is rotated at a constant angular velocity by a motor-driven pulley. The centripetal force is measured by passing the radial string holding the mass around a pulley in the central tube and connecting it up the vertical tube to the spring scale. The angular velocity can be varied by rotating a knob on the front of the motor. The centripetal force can be calculated by measuring the angular velocity with a digital clock or a manual timer (available upon request).
    OS11