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PHYS104

  • B3-03: LEVER - WRECKING BAR

    B3-03
    Demonstrate the mechanical advantage of a lever
    Use the lever to pry a large nail out of a 4"x4" pine wood beam.
    B3, tools

  • C2-11 RACING BALLS

    C2-11
    Illustrate linear kinematics

    Two balls are launched by a spring-operated launcher from one end of the track. They depart with the same velocities and the same kinetic energy imparted by the spring. As shown in the picture, one track runs in a straight line; the other dips down, runs straight for a time, then rises back up to the original level.
    Engagement Suggestion:
    Have students make predictions (and justify them):
    • Which ball will reach the end first, or if they will reach the end at the same time?
    • Which one (if either) will be moving faster at the end?
    Background:

    The ball on the straight track retains essentially the same velocity and the same kinetic energy throughout the length of its run, the kinetic energy from the spring. The ball on the dipped track, however, has a more complex path. When it goes downhill, it gains kinetic energy from gravitational potential, accelerating it. It travels along the lower section of track with this increased kinetic energy, and thus greater velocity. The ball then goes uphill again, losing that additional kinetic energy – it has returned to the same height, so the principle of conservation of energy dictates that it must return to the same gravitational potential as before, giving up kinetic energy equal to what it gained. It now has only the same kinetic energy it started with, as imparted by the spring. So its velocity is now the same as its starting velocity, and the same as the velocity of the other ball.

    However, during the time it was on the lowered section track, it had greater kinetic energy and greater velocity, so it traveled that distance faster than the ball on the straight track. And thus the ball on the dipped track reaches the end first, but with the same final velocity and the same final kinetic energy.
    OS0

  • C2-21 PROJECTILES DROPPED AND SHOT

    C2-21
    Demonstrate the independence of horizontal and vertical components of motion

    A latchable spring launching mechanism is mounted at the top of a stand. Two metal cubes are attached to the mechanism. When the latch is released, one cube will be projected horizontally while the other is dropped straight down. They strike the floor at the same time.
    Engagement Suggestion
    • Before showing the experiment, challenge students to predict what will happen. Will the horizontal motion of one pellet make it strike the floor before or after the other?
    • Afterwards, discuss why or why not.
    Background

    The gravitational force on each of the cubes is the same, so they experience the same downward acceleration. So since they started from the same height with zero vertical velocity, they reach the floor at the same time, even though one has traveled some distance horizontally in the meantime.

    This is an example of the independence or separability of the components of motion. We can define the axes along which we measure, and treat vectors as the sum of their components along those axes.
    FS2

  • C3-05 INERTIA - PEN IN BOTTLE

    C3-05
    Dramatically demonstrate inertia

    A large-tip felt pen is balanced on a 12" embroidery hoop, which in turn is balanced on a wide-mouth bottle. Yanking the hoop out from under the pen (by striking inside the leading side horizontally) allows the pen to fall straight downward into the bottle. Note that this does take a bit of practice; try it out before class.
    Engagement Suggestion:
    Ask your students: • Why does it matter if the hoop moves up or down while you are moving it?
    • Does it make a difference if you grab the hoop from the outside or the inside?
    Background:

    Newton’s First Law of Motion states that an object’s velocity is constant unless there is a net force acting on it. What this means is that if an object is not moving (at rest), it will not start moving until there is a force pushing or pulling on it. If an object is moving at a constant speed and direction, it will keep going with that same speed and direction unless a force pushes or pulls on it to change that. When the pen is sitting on top of the hoop, the force of gravity is pulling it down, but the normal force of the hoop is exactly equal to the gravitational force and holds it up. If another force suddenly affects the pen (such as if you walk up and tap on its side, or jiggle the hoop up and down), that force could cause it to move, and probably fall.

    But if the hoop is snatched sideways quickly and smoothly, it does not give any force to the pen. Now the only force acting on the pen is gravity, and the pen falls straight down into the bottle.

    C3

  • C3-12 PENCIL AND PLYWOOD

    C3-12
    Dramatically demonstrate inertia

    A pencil is accelerated to almost the speed of sound by blasting it through a four-foot tube using a carbon dioxide fire extinguisher. The pencil will readily impale itself through a piece of 3/8" plywood. With a little bit of luck the pencil point will be virtually intact, although sometimes you need to re-sharpen it after the demonstration.

    CAUTION: Be sure that the hose fitting is securely attached to the tube and that the plastic shield is in place before firing. The shield should be latched in place, with no debris blocking its edge from meeting the baseplate

    Engagement Suggestions
    • • Before using, encourage your students to predict what will happen to the pencil.
    • • For advanced students, discuss the energy involved in the problem and where the kinetic energy of the pencil went after the collision.
        • Background

        This demonstration can be presented in multiple ways. It has been offered classically as an illustration of the principle of inertia – the pencil is in motion at a high velocity, and continues in motion despite the intervening wood until arrested by a greater force. Alternatively, consider the high velocity and high momentum of the pencil. The abrupt deceleration at the plywood means a high impulse. The pointed pencil has a very small cross-sectional area, resulting in force applied over a small area leading to a high momentary pressure.

        Linked below is a slow-motion video of the collision, shot at 600 frames per second. A fun class activity could be to use the video to measure the motion of the pencil and estimate its momentum and kinetic energy, based on what you see in the video and by measuring typical lengths and masses for wooden pencils.

    FS1

  • 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.

  • C4-33 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

  • C5-13 WATER ROCKET

    C5-13
    Demonstrate Newton's third law of motion
    Air is compressed in the rocket by means of the pump; when the air is released, the rocket rises by a small amount. If a small amount of water is poured into the air compartment from the squeeze bottle pictured at the right and air compressed in the rocket to the same pressure as before, the rocket will rise very high when released. Due to its greater mass, the water exhaust has more momentum than the air; thus more reaction force is applied to the rocket by the exhausting water.
    C5

  • 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

  • C5-17: ROCKET BOTTLE

    C5-17
    Illustrate the rocket principle in a dramatic way
    Pour about 100-200 ml of liquid nitrogen into the bottle and install the stopper. Exhausting nitrogen gas and liquid result in motion of the bottle. An untethered stopper is available for comparison.
    OS6, I0, F2

  • C5-19: ACTION AND REACTION - INSTRUCTOR AND CART

    C5-19
    Demonstrate action-reaction pairs in a dramatic way
    The instructor jumps off the cart and the cart moves in the opposite direction. The mass of the cart can be decreased by removing some of the lead bricks, but if the cart is too light it can become dangerous. Please be careful.
    FS1

  • C5-32: SAILING UPWIND - HAIRDRYER AND SAILBOAT

    C5-32
    Illustrate sailing upwind
    A sailboat is modeled by a toy car; the car wheels allow motion only in the forward/backward direction, thus performing the function of the keel. When the sail is set at the proper angle on the boat, and the wind blows at the proper angle onto the sail, the boat will move with some velocity component in the direction from which the wind is coming.
    C5, F5

  • C6-03: INCLINED PLANE - FRICTION WITH THREE BLOCKS

    C6-03
    Illustrate different coefficients of friction.
    As the inclined plane angle is steadily increased, the three blocks begin to slide in the following order: (1) teflon, (2) styrofoam, and (3) rubber.
    C6

  • 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

  • C7-17 SUPERBALL

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

  • C7-23: MEDICINE BALL AND SKATEBOARD

    C7-23
    Demonstrate large-scale collisions
    Throw medicine ball to student sitting on skateboard. Student sitting on skateboard can throw medicine ball off.

  • C7-43: AIR TABLE - SMALL - COLLISIONS OF PUCKS

    C7-43
    Demonstrate collisions of pucks on an air table in rooms not accessible by the large air table.
    This small air table can be readily moved on a small rolling cart into all physics classrooms. Both elastic and inelastic collisions can be demonstrated using a variety of puck masses. Velcro collars are used to create inelastic collisions.

    Also see a simulation of similar collisions here: https://www.myphysicslab.com/engine2D/billiards-en.html

    OS10

  • 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

  • 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