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PHYS161

  • 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

  • D1-41 ROTATING WATER BUCKET

    D1-41
    Demonstrates centripetal force and centrifugal reaction
    Put some water in the bucket and rotate the bucket in a vertical circle over your head. The centripetal force provided by your arm keeps the water bucket moving in a circle, while the centrifugal reaction keeps the water in the bottom of the bucket, as long as the rotational velocity is sufficient.
    D1

  • 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

  • D1-53 LOOP-THE-LOOP

    D1-53
    Demonstrates centripetal force and conservation of energy in a rotating object

    This track can be described as three segments: the long upright segment, the loop, and the shorter upright segment. If you begin by placing the ball on the long upright segment at a height equal to the height of the loop (2R), the ball will roll down the track, begin to climb the loop, and then fall off and roll away. You can then repeat this at increasingly higher positions until the ball makes it all the way around the loop and begins to climb the shorter upright segment. In either case, be ready to catch it as it falls off afterwards!

    This is a good demonstration to encourage students to make predictions about its behaviour. Invite students to make arguments about what starting height will allow the ball to complete the full loop. A meter stick can be additionally provided upon request to aid in measuring the height.

    Background
    Motion of the ball down the track and around the loop-the-loop can be described in terms of gravitational potential energy, rotational and translational kinetic energy, and centripetal force. A ball of mass m and radius r must be released at some minimum height h above the bottom point of the track so that it will not leave the track while passing around the loop-the-loop.

    In order to stay on the track at the top of the loop the centrifugal reaction of the ball on the track must be equal to or greater than the gravitational force on the ball: mv^2/R = mg, or v^2 = gR, where v is its linear velocity at the top of the loop, R is the radius of the loop, and g is the acceleration of gravity. Conservation of energy dictates that at the top of the loop Iw^2/2 + mv^2/2 +2mgR = mgh, where the moment of inertia of the ball I = 2mr^2/5 and w is the angular velocity of the ball at the top of the loop.

    From these considerations we obtain the minimum starting height for the ball above the bottom of the loop-the-loop in order that the ball remain in contact with the track at all times: h = 2.7 R. In the case of an object sliding along a frictionless loop-the-loop, the height would be h = 2.5 R. Marks have been made at the points 2.5 R and 2.7 R. The ball remains in contact with the track at the top of the loop only when the height 2.7 R is reached, demonstrating the effect of the rotation of the rolling ball.
    FS2

  • D2-01 RING AND DISC ON INCLINED PLANE

    D2-01
    Demonstrates effect of rotational inertia on acceleration of an object

    A solid disc and a thin ring having the same mass and the same radius roll down an incline starting at rest from the same position. The roller with the greater moment of inertia, in this case the ring, rolls more slowly.
    Engagement Suggestion
    • When presenting the demonstration, encourage students to make a prediction before showing the roll. Will the two objects reach the bottom at the same time, or will one get there first? Which one?
    Background
    The effect of rotational inertia on the speed of a rolling object can be confusing to new students, especially those who have just recently internalized the principles of linear motion. Having just un-learned misconceptions about objects in free fall and discovered that objects experiencing the same force fall at the same rate regardless of mass, it can be counterintuitive to realize that the corollary does not apply in rotational motion. The distribution of mass does itself affect the torque on an object and how fast it rolls.

  • 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

  • D2-31 OBERBECK CROSS

    D2-31
    Illustrates rotational analog of Newton's second law of motion
    Various masses M can be hung on a string wound around an axle of either of two radii R to provide a torque T = MgR. Four brass masses m can be positioned along the arms at one of four distances l from the axis of rotation to provide a moment of inertia I = 4ml^2. The angular acceleration a = T/I = MgR/4ml^2 can then be calculated. The angular acceleration can be determined experimentally by measuring the time required for the system to rotate one complete revolution starting from rest: a = 2 d/t^2, where t is the time required for the device to rotate through the angle d in radians.
    FS1

  • 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

  • D3-03 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

  • D4-03: BICYCLE WHEEL GYROSCOPE ON PIVOT

    D4-03
    Demonstrates gyroscopic precession and nutation
    Spin the bicycle wheel and release it with a small push to obtain pure precession, or release it without simultaneously pushing it to obtain precession with nutation. Release it with no spin to show that precession only occurs with the pre-condition of angular momentum of the wheel.

  • F1-06 WATER SEEKS ITS OWN LEVEL

    F1-06
    Shows that pressure is dependent on depth, not shape of container

    This set of conjoined glass tubes is filled with green-dyed water. The water level in the four different tubes is the same even though the volumes and shapes of the tubes are very different.

    Engagement Suggestion
    • For advanced students, consider tilting the tubes slightly, then plugging them with corks so that the different amounts of trapped air cause the water to be at different levels. Challenge students to analyze why this changes the results, then remove the corks to show what happens.
    Background

    This illustrates that the pressure in an open container of liquid is dependent only on the depth, not the shape or area.

  • F2-01 ARCHIMEDES' PRINCIPLE

    F2-01
    Demonstrates the buoyant force on a body submerged in a fluid to be equal to the weight of the displaced fluid.
    Hanging from the balance are a hollow can and a solid cylindrical metal block of the same volume V. Lowering the metal block into a beaker of water results in a buoyant force equal to the weight of a volume V of water. Pouring the volume V of water into the can restores the original weight as read on the spring scale.
    FS2

  • F2-05 BUOYANCY - BOAT AND ROCK

    F2-05
    Illustrates buoyancy
    Boat and rock float in a closed pond. removing rock from boat and dropping it in pond will cause the water level of the pond to go down
    F2

  • F2-06: BUOYANCY - SINKING BOAT

    F2-06
    Illustrates buoyancy
    A heavy copper "boat" floats in a fish tank "pond," as seen in the photograph at the left. The water level in the pond is marked by the top of the black tape on either side of the tank. A cork is removed from a hole in the bottom of the boat, allowing the boat to fill with water and sink. As the boat sinks, the water level in the pond goes down

  • F5-06 BEACH BALL - COANDA EFFECT

    F5-06
    Illustrates the Coanda effect.
    A beach ball can be floated in the air stream provided by an air blower or vacuum cleaner. The ball remains in the air stream even when the air stream is significantly tilted. As the air flows past the ball, the air flow curves around the surface of the ball, due to the Coanda effect. The reaction force on the ball levitates the ball in the airstream.

  • F5-22 VENTURI TUBE WITH PING PONG BALLS

    F5-22
    Illustrates the venturi effect.
    In this Venturi tube the levitation of the ping pong balls in an airstream is used as a pressure sensor; the higher the ball the greater the pressure of the air coming from that hole. Both the venturi effect and the reduction of pressure along the tube can be seen.

  • G1-01 EXAMPLES OF SIMPLE HARMONIC MOTION

    G1-01
    Illustrates simple harmonic motion

    This demonstration lets you compare three typical pendula: a simple pendulum (mass on string), a physical pendulum (swinging rod), and a mass on a spring. Any of these produce simple harmonic motion, with a variety of periods. Useful for showing that the same equation describes the motion of any type of oscillating body.
    You can also compare these real-world pendula with some simulated ones:
    1. Erik Neumann's Single Spring simulation
    2. Erik Neumann's Pendulum simulation
    3. PhET Masses on Springs
    4. PhET Pendulum Lab
    FS2

  • G1-11 COMPARISON OF SHM AND UCM

    G1-11
    Demonstrates the relationship between simple harmonic motion and uniform circular motion.
    Turning a crank on the rear of the apparatus causes the center ball to move in circular motion around a 30cm diameter orbit, while the ball on top executes simple harmonic motion. It can be seen that SHM is the projection of UCM. This device can also be used to discuss the concept of degrees of motion in SHM by comparison with the reference circle.

  • G1-14 PENDULA WITH DIFFERENT MASSES

    G1-14
    Demonstrates independence of a simple pendulum's period with mass of the bob.
    Four geometrically identical pendula have bobs made from lead, brass, stainless steel, and aluminum, respectively. Their periods are the same.
    FS2