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PHYS171

  • B1-06: Double Cone - Large

    B1-06
    Demonstrate a center-of-mass paradox
    When a double cone is placed on the narrow end of a V-shaped rail, the cone will roll towards the wider end of the rail when released. The cone appears to be rolling uphill (from the narrow end to the wider end), but in reality the center of mass is moving down. Upon special request, we can also provide a cylindrical rod of the same length as the double cone to roll along the rails to show their actual slope. Challenge students to predict whether the cylindrical rod travel in the same direction as the double cone.

    Note: B1-07 is a smaller, more portable version of this demonstration.
    B1

  • C1-02: CENTER OF MASS MOTION - PLUMBER'S HELPER

    C1-02
    Illustrate the motion of the center of mass of an irregularly-shaped object.
    The center of mass of the plumber's helper is located by a bright red tape. When the object is thrown through the air with some rotation, the center of mass moves in a smooth parabolic arc.
    C1

  • 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

  • C2-22 MONKEY AND HUNTER

    C2-22
    Demonstrate the independence of horizontal and vertical components of motion
    A physical example of a classic textbook illustration, this demonstration shows the independence of the components of motion and the equal acceleration of bodies due to gravity.

    The launcher is aimed at the monkey and shot. As the projectile leaves the muzzle of the gun it breaks a circuit producing the magnetic field which holds the monkey in place. The monkey then begins to fall at the same time the projectile is fired directly at the monkey. Due to independence of horizontal and vertical components of motion, the projectile will strike the monkey.

    Note that the angle can be varied to show different horizontal and vertical components.
    FS1

  • C2-25: FUNNEL CART

    C2-25
    Demonstrate the independence of horizontal and vertical components of motion
    A ball is placed in the funnel and the funnel cocked by compressing a spring. The cart is then pushed across the track. At a certain point a bump below the track trips a lever, releasing the spring and ejecting the ball vertically. Because the ball and the cart both move with the same horizontal speed, the ball stays directly above the funnel at all times, and falls back into the funnel. Before doing the experiment, ask your students where the ball will fall: in front, behind, or in the funnel.
    C2, OS0

  • C2-26 FUNNEL CART WITH MASS OVER PULLEY

    C2-26
    Demonstrate the independence of horizontal and vertical components of motion
    A ball is placed in the funnel and the funnel cocked by compressing a spring. A mass on a string passing over a pulley is attached to the funnel cart, and the cart released so that it accelerates across the track. At a certain point a bump below the track trips a lever, releasing the spring and ejecting the ball vertically. Due to the acceleration of the cart, the ball falls behind the funnel.
    C2, OS0

  • C2-27 FUNNEL CART ON INCLINE

    C2-27
    Demonstrate the independence of horizontal and vertical components of motion
    A ball is placed in the funnel and the funnel cocked by compressing a spring. The track is raised at one end so that when it is released the cart accelerates down the track. At a certain point a bump below the track trips a lever, releasing the spring and ejecting the ball perpendicular to the track
    C2, OS0

  • C3-02 INERTIA - TABLE CLOTH TRICK

    C3-02
    Dramatically demonstrate inertia
    The table setting rests on a silk tablecloth. Rapidly yanking the tablecloth out from under the setting pieces leaves the table setting unchanged.
    C3

  • C3-03 INERTIA - MASSES HANGING IN SERIES

    C3-03
    Dramatically demonstrate inertia
    Two identical masses are hung in series from a fixed point alternating with three identical strings. When you pull downward on the third (bottom) string, which of the strings will break: the top, the middle, or the bottom string? It depends on how you pull. If you pull very quickly, the bottom string will break, due to the inertia of the bottom mass. If you pull slowly, the top string will break, because the weights increase the tension in the top string.
    FS2

  • C3-04: INERTIA - LEAD BRICK AND HAND

    C3-04
    Illustrates inertia of rest

    Place the lead brick gently on your fingers and strike the lead brick sharply with the hammer. The inertia of the lead brick prevents damage to your fingers.

    Engagement Suggestion
    • This is a visually impressive way to get students’ attention at the beginning of a discussion of inertia.
    • This can be used as a volunteer participation demonstration, but please be very careful.
    C3

  • C4-21 ATWOOD MACHINE

    C4-21
    Illustrate the second law of motion. Experimentally determine the acceleration due to gravity.

    This classic demonstration illustrates motion under the acceleration of gravity. When used carefully, approximate measurements can be made.

    Equal masses M of 200 grams are hung on the ends of a light string passing over a light, frictionless pulley. When an additional mass of 100g is hung on one end, the resulting acceleration can be measured by timing the motion of either mass over a distance S between two points. The acceleration of gravity g can then be calculated: g = a (2M + m)/m, where a is the acceleration of the system: a = 2S /t^2.
    C4, FS2, ME1

  • 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

  • C4-52 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

  • C5-13 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

  • C5-18 FAN CART

    C5-18
    Demonstrate Newton's third law of motion
    This small wheeled cart has a battery-powered fan mounted on it, and a slot at the end that can hold a plastic sail. With the sail off, turning on the fan drives the cart in the direction opposite the blowing air. With the sail on and the fan off, blowing on the sail will drive it in the direction you blow. With the sail on and the fan on, the sail visibly flexes, but the cart goes nowhere at all. The force acting on the sail is such that it exactly cancels.

    Note: The fan spins quite fast. Don't let it hit your fingers! To connect and disconnect power, use the alligator clip wire on the rear; clip it to the fan support frame for safety when not in use.

    Consider inviting students to make predictions about the cart's behaviour with and without the sail. Invite them to discuss the forces involved.
    C5

  • 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

  • C6-02: INCLINED PLANE - FRICTION BLOCK

    C6-02
    Demonstrates that the coefficient of static friction is greater than the coefficient of sliding friction, and determines the coefficient of static friction.
    Position the block on the incline and slowly increase the angle until the block begins to slide down the incline. Because the coefficient of static friction is greater than the coefficient of sliding friction, after the block starts sliding it will continue to slide.
    C6