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  • C4-01: AIR TRACK - NEWTON'S SECOND LAW

    C4-01
    Demonstrate F = ma.
    A small mass hanging over a frictionless pulley provides the constant force which accelerates the glider between gates A and B. Using the photogate timing system, the time for the glider to travel from A to B can be measured, or the velocities of the glider at positions A and B can be measured using the 5 cm tab mounted on the glider. The accelerating force can be varied by adding additional masses, or gliders of mass M, 2M, and 3M (2M + M) can be used. A careful measurement should yield a result good to <10%.

  • C4-02 AIR TRACK - A eq F/M

    C4-02
    Illustrate the experimental basis for Newton's second law of motion
    This experiment uses the two gates to determine the time interval for the glider to be accelerated over the distance between them. You must therefore hold the glider so that the tab interrupts the photocell light beam immediately when the glider is released. The constant accelerating force is provided by a small mass hanging over a pulley on a low-friction tape connected to the glider.

  • C4-04: F=MA WITH ULI AND FORCE PROBE

    C4-04
    Demonstrate forces required to change the momentum of an air track glider.
    The Universal Laboratory Interface is used with an ultrasonic range finder and force probe to plot a graph of the motion as an air track glider approaches the end of the air track, bounces off the force probe with an approximately elastic collision, and returns in the opposite direction. The force probe measures and plots the force as a function of time during the collision of the cart with the end of the track at which the force probe is mounted. The integral of the force over the contact time is the impulse, which is equal to the change of momentum of the glider. The velocity as a function of time, plotted by the motion software, is used to independently determine the change in momentum of the glider.

  • C4-11: ACCELEROMETER - BALL IN WATER

    C4-11
    Demonstrate the direction of acceleration for both linear and circular cases.
    When the accelerometer is accelerated linearly, the ping-pong ball, being less dense than the water, moves toward the direction of the acceleration. When the jars are rotated the ping-pong ball moves toward the center of rotation.
    C4

  • C4-12: ACCELEROMETER ON INCLINED PLANE

    C4-12
    Illustrate the behavior of a liquid accelerometer accelerating down an inclined plane.
    When the liquid accelerometer is accelerated, as in the case of the photograph at the left above, the liquid moves in the direction opposite to the acceleration, because of its inertia. When it is held motionless on an incline, the liquid moves toward the downhill side. When the accelerometer is allowed to accelerate down the incline, it will line up with the surface of the water parallel to the inclined plane.
    C4, FS1

     

  • C4-13: ACCELEROMETER ON ROTATOR

    C4-13
    Show that the surface of a rotating liquid assumes a parabolic shape.
    This is the accelerometer from C4-12 mounted on a hand-cranked rotator. Rotate the accelerometer at a constant rate to show the parabolic surface. (A video camera can be provided in the lecture halls if needed.)
    C4, D1

  • C4-14: AIR TRACK - ACCELEROMETER

    C4-14
    Demonstrate the behavior of a liquid accelerometer.
    The glider/accelerometer assembly moves along the horizontal air track with the surface of the water parallel to the floor in the absence of acceleration. With the air track tilted, the surface of the water is horizontal when the glider is motionless, but becomes parallel to the air track when the glider accelerates down the incline. Various motions and accelerations of the glider can be studied, with the air track either level or tilted. The photographs above show the accelerometer at rest and freely accelerating down the tilted air track.

    B&W photo of cart traveling on inclined air track

  • C4-15: HELIUM BALLOON IN ACCELERATED BOX

    C4-15
    Illustrate the affect of density on acceleration in a counterintuitive way.
    A helium balloon is tethered to the bottom of an enclosed plastic box. If the box is accelerated, it will move in the direction of the acceleration.

  • 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

  • C4-31: AIR TRACK - THE ACCELERATION OF GRAVITY

    C4-31
    Experimentally determine the acceleration of gravity.
    One end of the air track is elevated at an angle a so that the glider will accelerate down the slope with some component of the acceleration of gravity. This component is determined experimentally by measuring the velocity v of the glider after it has accelerated a fixed distance S down the track. The angle a is determined from the amount the track is raised and the distance between the two support feet. The acceleration of gravity is then: g =v^2 /(2 S sin(a)).

  • C4-32: FREE FALL IN VACUUM - DISK AND FEATHER

    C4-32
    Demonstrate that bodies of extremely different densities fall with equal acceleration in the absence of air friction.

    This demonstration consists principally of a long glass tube containing a heavy disc and a brightly coloured feather. A nozzle and valve at one end of the glass tube allows the air to be removed from the tube using a vacuum pump. This allows the objects to fall with or without air resistance.
    Operation:
    • • Turn the tube vertically while still filled with air; show that the disc drops rapidly to the bottom end, and the feather flutters down slowly.
    • • Invite students to predict how this behaviour will change when the air is removed.
    • • Connect the pump and pump out most of the air. There will be an audible change in pitch when the tube is sufficiently evacuated, after 1-2 minutes.
    • • Turn the tube vertically again, and let the students see that both now fall at the same rate.
    • • CAUTION: The tube is thick glass; please handle with care.
    Background:

    The key physics in play here is twofold. Absent other forces, the two objects undergo the exact same acceleration in free fall, and so will fall at the same rate. With no air in the tube, the only force acting on them is gravity, which pulls downward on each object proportional to its mass.

    However, when air is in the tube, there is a second force involved: air resistance.

    The force of air resistance pushes upwards on the falling objects. It depends on two factors: the surface area of the falling object, and its velocity. So the faster they fall, the more resistance they face from the air. But recall that the force of gravity is proportional to the mass of the object, and the net acceleration of an object is the result of the sum of the forces acting on it. So if two objects have similar surface area, but one has a higher mass, then the higher mass one experiences a larger downward force than the other, while air resistance will exert close to the same upward force on both, and so the heavier object then has a greater acceleration. And that’s what we see when the tube is full of air – the more massive disc falls faster than the less massive feather. Take away the air and the force of air resistance, and they fall together!
    C4, I0, I4

  • C4-41: TERMINAL VELOCITY - BOTTLE IN TUBE

    C4-41
    An easily observable terminal velocity experiment.
    The bottle falls through the tube; close fit creates air friction, leading to a low terminal velocity. Adding water to the bottle increases the terminal velocity. Retrieve bottle quickly with string for repeated drops.
    OS0

  • C4-43: TERMINAL VELOCITY - STACKED COFFEE FILTERS

    C4-43
    Illustrate terminal velocity quantitatively.
    Stacks of different numbers of coffee filters are dropped from various heights. The viscous force is proportional to the square of the velocity, so the terminal velocity is proportional to the square root of the number of filters in the stack. A stack of four filters will have a terminal velocity twice that of a single filter; the stack of four will therefore take the same time to fall two meters that a single filter takes to fall one meter, as is being demonstrated by Gwen in the photograph.
    C4, OS0

  • C4-61: ACCELERATION ON A SCALE

    C4-61
    Illustrate forces in an accelerating system.
    A rigid frame hangs from a spring scale as photographed. In the frame, a mass hangs from a spring. The mass is pulled down and attached to a hook at the bottom of the frame by a short thread loop. (Ask your students how this affects the weight shown by the spring scale.) In this position the spring scale reads about 8 Newtons. Q: When the string is burned, releasing the mass, will the reading on the spring scale immediately after the string breaks (a) increase, (b) decrease, or (c) stay the same? A: It will increase, as seen on the accompanying mpeg video. The last photograph shows details of the lower connection of the weight to the hook.

  • C5-01: NEWTON'S THIRD LAW - STATIC DYNAMOMETERS

    C5-01
    Demonstrate action-reaction in the static case
    The dynamometer springs have been arranged so that the upper meter measures the force pulling down on it, while the lower meter measures the force pulling up on it, including its own weight. Pulling down on the hook below the lower meter results in a pair of equal and opposite forces acting on the coupling washer.
    FS2

    c5-01a

  • C5-11: AIR TRACK - ACTION-REACTION PAIRS

    C5-11
    Demonstrate Newton's third law of motion
    Two gliders (either M and 2M or M and M) are tied together with a string loop against the force of a compressed spring. Burning the string releases the gliders with no external force. The photogate timer measures the time it takes for each glider tab to move through its respective gate. A reset switch on a cable clears the timer between measurements without the instructor getting in the line of sight.

  • C5-16: HERO'S ENGINE

    C5-16
    Demonstrate action and reaction in a rotational system.

    The boiler is partially filled with water and heated until steam is produced. The steam emerges from right-angle arms on the side of the boiler, causing the boiler to rotate in the direction opposite to that of the emerging steam.

    Danger:Do not tilt burner until it is warm.
    C5, I0

  • C5-20: PUTT PUTT STEAM BOAT

    C5-20
    Demonstrate action-reaction using an intriguing device.

    The "putt-putt" or "pop-pop" boat is a classic toy rarely seen in the 21st century, and a fascinating example of a heat engine at work. A small heater using vegetable oil boils water, forcing out water and steam from the tailpipe of the boat. After the steam and water are expelled water is pulled back into the boiler. This process produces a net force in the forward direction, propelling the boat forward. Refer to the geometry of the boat boiler system (above) to further understand this phenomenon.

    This is similar to the processes by which the inverse sprinkler is driven in the forward and the reverse directions to cause the direction of rotation to reverse for the inverse sprinkler.

    Note: Be sure to completely fill the boiler chamber with water before heating it. Practice lighting the wick.

    c5-20a

  • 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