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PHYS131

  • A1-03: DENSITY - VARIOUS BRICKS

    A1-03
    Demonstrate the concept of density
    This demonstration consists of several bricks of approximately the standard "brick" size and shape, made of various materials such as foam, concrete, steel, and lead. Because the sizes are similar and the weights different, the feature creating the difference must be the density, or mass per unit volume. Invite students to make predictions about which will be heavier, then come up to pick them up and test their predictions.
    OS6

  • A1-31: VOLUME MEASURE DEMONSTRATION

    A1-31
    Illustrate metric volume units
    Two 1000 cc (1 liter) blocks are available, from which smaller units of volume (100cc, 10 cc and 1 cc) can be removed. Note that the smallest units are easily lost, so it is best to have students come to the lecture table to examine the models, rather than passing them around.

    This can also be useful to show in conjunction with discussions of estimation, eg "Fermi Problems."
    A1

  • A1-32: VOLUMES - SPHERICAL VS CYLINDRICAL

    A1-32
    Illustrate a volume perception paradox
    Water filling the graduated cylinder is poured into the apparently smaller spherical flask. While the spherical flask may appear to students to be much smaller than the tall cylinder, this enables them to see that it actually has the same volume.

    Invite students to make a prediction about how much of the cylinder will fit in the sphere, or how much it will overflow, before performing the experiment.
    A1

  • B4-01 HOOKE'S LAW

    B4-01
    Demonstrate the linear relationship between force and stretching for a simple spring.
    Two weights are provided to show linearity over a factor of two in applied force.
    FS2

  • B4-03: SPRINGS IN SERIES AND PARALLEL

    B4-03
    Show static combinations of springs
    Two springs with approximately the same spring constant can be placed in series and parallel to determine the effective spring constants. You should be able to illustrate the relationships:

    k(parallel) = k(1) + k(2)

    1/k(series) = 1/k(1) + 1/k(2)

    B4, FS1, OS0

  • B4-11: ELASTIC LIMIT OF RUBBER BAND

    B4-11
    Demonstrate Hooke's law and elastic limit.
    Load small weights to demonstrate Hooke's law. Hanging a few kilograms from the rubber band exceeds its elastic limit.
    FS2, ME1

    b4-11a

  • C1-21: AIR TABLE - TOPPLING STICK

    C1-21
    Illustrate how a rigid rod topples on a frictionless surface.
    A wooden dowel with its center of mass marked is held vertically with the bottom end supported by a very light air table puck. When it is released and allowed to topple, which point of the stick will be directly above the original support point: the top end, the bottom end, or the center of mass? Note that the stick has a small counterweight on its top end to compensate for the mass of the puck. Click your mouse on the photograph for an mpeg video.
    FS0

  • C2-06 BALL DROP ON ROPE - EQUAL AND UNEQUAL INTERVALS

    C2-06
    Illustrate the geometrical effect of free fall
    Two ropes of equal length have steel balls tied at five points along their length. One rope has the balls at equal distances along the rope, while the second has balls positioned geometrically, at distances proportional to the squares of integers: 1, 4, 9, 16, and 25. When the first rope is dropped the equally spaced balls hit the floor at progressively shorter time intervals; when the second rope is dropped, the geometrically positioned balls hit the floor at equal time intervals. NOTE: This demonstration can only be properly done in the lecture halls because it requires 12 feet of height to fully extend the ropes.
    C2

  • 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

  • C2-25: 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

  • C2-28: TRAJECTORY OF BALL DROPPED BY WALKER

    C2-28
    Demonstrate the independence of horizontal and vertical components of motion
    The subject walks along a line with their arm straight out holding a ball. Have the students make suggestions as to, as the subject passes a bucket, where must they release the ball so that it will fall into the bucket?
    OS3

  • C2-41: VECTOR ADDITION OF VELOCITIES

    C2-41
    Illustrate addition of two orthogonal velocity components
    A billiard ball is placed at the corner of the apparatus. When the two mallets are pulled back and released they strike the ball simultaneously, giving it two orthogonal velocity components. The relative amount of each component is determined by how high each mallet is raised. Use the floor tiles to define your coordinates and show that equal forces in two orthogonal directions produce motion at 45 degrees with respect to the axes.
    C2

  • C2-51: KINEMATICS WITH ULTRASONIC RANGER

    C2-51
    Plot graphs of position, velocity, and acceleration

    The ultrasonic range detector is used with a computer to plot graphs of position, velocity, and acceleration. Linear motion can be created by a person walking along a line in front of the ultrasonic ranger. A large piece of styrofoam sheet can be used as a reflector for the ultrasound, to keep the curves as smooth as possible. Graphs of x, v, and a can be easily displayed individually or in any combination.

    The graphs of position and velocity are quite nice, but the acceleration can be a bit noisy, because it is obtained by differentiation of the position vs. time data. Try this before class.
    C2, FS1

  • 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

  • C4-03: ACCELERATION BY ITERATED BLOWS

    C4-03
    Illustrate the numerical technique by which a computer carries out integration of the equation a = F/m.
    The bowling ball is accelerated by a series of small blows with the mallet. Both linear and centripetal acceleration can be illustrated.
    C4

  • 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

  • C4-33 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