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PHYS141

  • C4-33 FREE FALL IN VACUUM - FEATHER AND BALL

    C4-33
    Demonstrate that bodies that fall with unequal accelerations in air fall with the same acceleration in the absence of air.
    The ball falls faster than the feather with air in the tubes. When the air is pumped out, the ball and the feather fall with the same acceleration. The double tube assembly is rotated rapidly on its axis to initiate the free fall.
    FS1

  • C4-34: GALILEO'S EXPERIMENT - MASSES IN FREE FALL

    C4-34
    Show that the acceleration of bodies in free fall is independent of mass
    Light and heavy balls are weighed using the spring scale. When they are dropped simultaneously from a height of about ten feet, they accelerate downward at the same rate (the acceleration of gravity) and reach the floor at the same time. A wooden board acts as a sound board to amplify the sound when they reach the floor.
    C4, OS0

  • C4-52 WEIGHTLESSNESS IN FREE FALL - MASS IN CUP ON POLE

    C4-52
    Illustrate apparent weightlessness in free fall
    A mass hangs from a spring over the edge of a cup. Raise the pole vertically and release. Because the mass becomes weightless in free fall, the ball will be pulled into the cup immediately when the system begins to fall.

  • C5-02 SPRING AND PULLEY PARADOX

    C5-02
    Show that the action-reaction pairs have equal magnitude
    Initially, set this up with the horizontal spring scale facing away from your students. The mass on the hanger pulls down on the vertical spring scale with a force W equal to its weight. Challenge your students to predict what the other scale will read. After discussion, turn it to reveal: The spring scale reads the weight of the mass even thought it is horizontal between the pulleys
    FS2

  • C5-12: BALLISTIC CANNON CARTS

    C5-12
    Demonstrate Newton's third law of motion
    The carts, initially at rest, are placed at the center of a level track as photographed. The cannon fires its projectile into the receptacle on the other cart when a string is burned, releasing a spring. The mass of the projectile plus the mass of the receptacle cart equals the mass of the cannon cart, so if the carts are started in the middle of the track they will move away with equal but opposite velocities and reach their respective ends simultaneously.
    C5, OS0

    c5-12

  • C5-14 ROCKET TRIKE

    C5-14
    Demonstrate Newton's third law of motion

    Pressing the fire extinguisher handle expels carbon dioxide out a nozzle straight behind the tricycle, causing forward thrust of the tricycle. Be sure the exhaust is not oriented to hit the audience or anything else likely to be adversely affected but a sudden blast of cold air.
    Background
    This is a dramatic illustration of Newton's Third Law of Motion: the principle of action and reaction. The mass of gas being ejected out of the back of the tricycle at a very high velocity imparts an equal and opposite force to the tricycle, which thus moves forward. The tricycle is much more massive, so it does not move as quickly, but the acceleration is still very real - be careful not to run into the wall!
    FS1

  • C5-31: AIR TRACK - SAILING UPWIND

    C5-31
    Show how force components can be used to sail against the wind.

    A sail is attached as shown to an air track glider. Wind from a fan blows the sailboat in the direction from which the wind is coming if the angle between the wind and the sail is correct.

    Click your mouse on the link below to see a video of the action. After the video begins, (a) the air cushion is turned on, then (b) the air gun is started, creating the force situation shown in the drawings below.

    c5-31b

  • 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

  • C7-04: 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

  • C7-18 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

  • C7-25: 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

  • 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

  • C8-33: 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

  • D1-30: TRAJECTORY FROM CIRCULAR ORBIT - OVERHEAD PROJECTOR

    D1-30
    Show that the instantaneous velocity of an object executing uniform circular motion is tangent to the circle.
    A marble is rolled around the inside of the circular band on an overhead projector. 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.

    A transparent sheet is available with an outline of the circle and various possible paths. This can be used to challenge the students to guess the outcome of the experiment before performing it.

    Compare D1-31 and D1-32, other demonstrations showing similar effects.
    D1

  • D1-39: PENNY AND COAT HANGER

    D1-39
    Demonstrate centripetal force and centrifugal reaction in a dramatic way.
    Balance the penny (face up) on the flattened coat hanger tip, as shown in the photograph. Start slowly swinging the hanger back and forth like a pendulum, then rotate it in a complete circle. With practice, it is possible to rotate the system several times and stop the motion without dislodging the penny.
    D1