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PHYS171

  • 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.

  • C7-15 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

  • C7-17 SUPERBALL

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

  • 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

  • C8-11 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

  • C8-14 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

  • 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

  • D1-51 BANKED CURVE MODEL

    D1-51
    Aid in explaining banked turns
    The model of the curved road is banked such that at the suggested maximum rate of speed the horizontal component of the normal force provides the centripetal force required to keep the car moving in its circular path, independent of the friction of the car wheels with the road.
    D1

  • D1-61: Rolling versus Sliding

    D1-61
    Applies conservation of energy to a rolling object

    An aluminum cylinder rolls down an inclined plane. An identical aluminum cylinder has tiny bearings on one end, so that it slides without friction down the incline.

    Invite the students to make a prediction: If the two cylinders are started from the top at the same time, will the rolling cylinder or the sliding cylinder reach the bottom of the incline first?

    Background
    The two cylinders start at the same height with the same potential energy. As they slide or roll down the ramp, that potential energy is converted into kinetic energy. Linear kinetic energy is proportional to the mass of the cylinder and the square of its velocity. However, the rolling one also has rotational kinetic energy, which is proportional to the moment of inertia of the cylinder and the square of its angular velocity. So for the rolling cylinder, some of the potential energy is converted into rotational kinetic energy as it rolls, and only some of the potential energy is converted into linear potential energy, giving it a lower velocity as it goes down the ramp. So the sliding cylinder reaches the bottom first.
    D1, FS2

  • 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.

  • D1-65: 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.

  • D2-02: Miscellaneous Rolling Bodies On Inclined Plane

    D2-02
    Demonstrates effect of rotational inertia on acceleration of an object
    Different objects are rolled from rest down an incline, and their accelerations compared. The acceleration is less for those bodies with the smaller radius of gyration (square root of the moment of inertia per unit mass). Available rollers include rings, discs, and solid spheres of different masses and radii.
    D2, FS1

  • D2-05: DUMBBELL - VARIABLE MOMENT OF INERTIA

    D2-05
    Demonstrate the effect of moment of inertia.
    Hold the dumbbell at its center and rotate it rapidly in alternating directions. Then change the moment of inertia by sliding the weights along the rod. See how moment of inertia affects the speed and effort with which you can change rotation.
    D2

    d2-05a

  • D2-11: HINGED STICK AND FALLING BALL

    D2-11
    Application of the rotational analog of Newton's second law.

    The hinged stick is held in place as shown with the ball balanced on the end of the stick. When the stick is released, it accelerates faster than the ball, so the ball falls into the cup.

    Note that the initial position of the ball is directly above the final position of the cup!

    Download the mpeg below for a brief clip of the demonstration in action.
    D2

    d2-11a

  • D3-01 MASSES SLIDING ON ROTATING CROSSARM

    D3-01
    Illustrates conservation of angular momentum
    Two masses which can slide along a crossarm can be moved to smaller radii by pulling on the chain hanging down through the center of the apparatus. With the masses at the largest radius, start the system rotating. Pulling the chain pulls the masses inward, reducing the moment of inertia and causing the system to rotate with a greater angular velocity. Conversely, slowly releasing the chain increases the moment of inertia and thus reduces the angular velocity.
    D3

  • D3-02: MASS ON STRING - ORBITS WITH VARYING RADIUS

    D3-02
    Illustrates conservation of angular momentum
    Rotate the mass on the string with the central end of the string passing through the tubular metal collar. Pulling the string decreases the radius of the ball, thus decreasing the moment of inertia and increasing the angular speed of the ball.
    D3

  • D3-03 ROTATING CHAIR AND WEIGHTS

    D3-03
    Illustrates conservation of angular momentum

    A subject, holding the weights with their arms extended, is started into rotation. When the weights are pulled inward to the chest of the subject, the moment of inertia of the system is decreased, leading to significant increase in the angular speed of the rotating chair.

    Please take care when using this device, especially when accelerating. You can gain a significant increase in rotational speed, so hold on! And it is best not to have a person push the chair around very much, as it is very easy to hit them with a weight by accident.

    Engagement Suggestions
    • Consider inviting a participant from the class.
    • Encourage students to predict what will happen before performing the demonstration.
    • Once the demonstration has been performed, discuss the activity both in terms of angular momentum and its conservation, and in terms of kinetic energy.
    • For extended discussion, introduce the idea of friction. How does friction work in this system? How does it affect the angular momentum? Where does the kinetic energy go?
    Background
    This device illustrates the conservation of angular momentum. When the heavy weights are moved closer to or farther from the axis of rotation, the distribution of mass and thus the rotational inertia (or moment of inertia) changes.

    To show this in a different way, a single user with a single weight can move themself in a circle by swinging their arm wide holding the weight from front to back, then drawing it inwards before extending their arm forwards again and repeating the motion. This is essentially a rotational analogue of pumping a swing.
    FS0

  • D3-05 ROTATING CHAIR AND BICYCLE WHEEL

    D3-05
    Illustrates conservation of angular momentum

    Sit on the chair (chair not rotating) with the wheel spinning and its axis oriented vertically. Reverse the angular momentum vector of the wheel by inverting the wheel, thus causing the entire chair to rotate in the original direction of the wheel rotation. Returning the wheel to its initial orientation causes the chair to cease its rotation.

    Because the friction in the bearing of the rotating chair is very low, several cycles of this procedure can usually be completed before the system loses its energy and stops.

    Engagement Suggestions
    • Consider inviting a participant from the class.
    • Note that this demonstration can lead to sudden changes in motion. Be careful not to collide with your volunteer.
    FS0

    Bicycle Wheel Gyro v2