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Applications of Newton's Laws

  • B2-36: EQUILIBRIUM OF TORQUES ON METERSTICK - ROTATORS

    B2-36
    Demonstrate equilibrium of torques

    Balance the meter stick ASYMMETRICALLY on the two rotators, and start the rotators in motion. Then balance the meter stick as close to SYMMETRICALLY as you can and start the rotators. It will always fall off if the rotators rotate outward, and will always end up balanced with the CM in the center if the rotators rotate inward. Which direction it moves depends on very small asymmetries!! Click the links below for several cases:


    Rotators rotate inward, meter stick starts asymmetrically balanced.

    Rotators rotate outward, meter stick starts asymmetrically balanced.

    Rotators rotate outward, meter stick starts symmetrically balanced and falls to the left.

    Rotators rotate outward, meter stick starts symmetrically balanced and falls to the right.


    Try different starting points. Try adding a 100 gram weight onto either end. (Please ask for the weight so we do not overlook it.) It always works. Ask your students what they think will happen before doing the original experiment. Ask them again after adding a weight to one side.
    B2

    st

  • B2-42: ARM MODEL

    B2-42
    Model the forces occurring in the arm

    Photograph at the top shows arm model in neutral force configuration

    Force applied by the biceps (lower left), pulling up with the hand: Apply 2.5 kg to the biceps cable to support the unloaded forearm. The forearm may be kept at equilibrium by the simultaneous addition of masses in the ratio of 10:1 at the biceps and at the hand. The torques are balanced almost independently of the angular position of the arm.

    Force applied to the triceps (lower right), pushing down with the hand: Hang the spring scale between the top hook and the hand hook, and attach the hanger to the triceps cable. Add masses to the hanger to determine how much force in the triceps is necessary to push down with the force read on the scale.
    FS2

     

  • B2-43: CRANE BOOM

    B2-43
    Demonstrate a crane boom
    The three configurations pictured may be readily set up and analyzed. The dynamometer measures tension in the rope; an internal spring scale measures the compression in the boom.

     

  • B3-01: LEVER AND LOADED WAGON

    B3-01
    Demonstrate the mechanical advantage of a lever
    The front of the cart can be lifted with the fulcrum one or two feet from the end of the lever. Even with one or two students on the cart, the cart can easily be lifted with a moderate downward force on the lever.
    FS1

  • B3-02: LEVERS - THREE CLASSES

    B3-02
    Demonstrate the three classes of levers

    Referring to the three photographs above:

    First class lever (top): the pivot is between the load and the applied force (push down with hand or pull down with spring scale at left in photo).

    Second class lever (lower left): the load is between the pivot and the applied force.

    Third class lever (lower right): the applied force is between the load and the pivot.



    Note: Look this over before class; you must change around the various components during the lecture.
    ME1, OS0

     

  • 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

  • B3-12 PULLEY - MECHANICAL ADVANTAGE

    B3-12
    Illustrate pulley systems
    The system is initially balanced to account for the weight of the pulleys and rope by adding small weights on the free end of the rope, as seen in the photograph at the left. For every two kilograms hanging from the pulley, the system requires one kilogram hanging from the free end of the rope to obtain equilibrium. Show that deviation from the 2:1 ratio destroys the static equilibrium.
    FS1

  • B3-21: CHISEL AS WEDGE

    B3-21
    Demonstrate the mechanical advantage of a wedge

    A wedge is used to split a piece of wood.

    For your safety, goggles are provided
    B3

  • B3-23: Worm Gear

    B3-23
    Illustrate mechanical advantage
    The worm gear is a simple machine which illustrates mechanical advantage. Using only a small torque, a relatively heavy weight can be lifted. Concomitantly, a fast rotation of the worm produces a slow angular displacement of the wheel. The mechanical advantage is 136.
    B3, FS2

  • C1-04: CENTER OF MASS - BEAR ON TIGHT ROPE

    C1-04
    Show stability in system where the center of mass is outside of the object.
    As the bear rolls along the tightrope, it remains stable because its center of mass is below the rope. Removing the weights and poles renders the system unstable.

  • 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

  • C4-41: 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

  • C4-61: 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.

  • 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

  • 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

  • C6-04: FRICTION DIRECTION ON INCLINED PLANE

    C6-04
    Determine the direction of the frictional force in a possibly ambiguous situation.
    Place weights in the box and hanging from the pulley such that the system is in static equilibrium. Add mass to the box until it begins to slip down the incline; the frictional force must be in the upward direction. Hang additional weight on the string over the pulley until the box begins to slide up the incline; the frictional force must be in the downward direction.
    C6, ME1

  • C6-05: AIR TRACK - INCLINED PLANE FRICTION

    C6-05
    Show that the force of friction depends upon the conditions of the surfaces in contact.

    With no air pressure on the tilted air track and an appropriate counterweight, the glider will be held in place by friction. Start the blower and, if the counterweight is sufficient, the glider will move up the incline.

    The pulley end of the air track is raised on one of the large wooden blocks. Using a small glider, as photographed, a 10-gram weight is insufficient to pull the glider up the track with the air on, and the glider moves down the incline. Adding the 20-gram weight (total of 30 grams) causes the glider to move up the air track with the air on.

  • 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

  • C6-12: SKIDDING AUTOMOBILE

    C6-12
    Demonstrate the effect of locked wheels on vehicle stability.

    A plastic toy car is lightweight enough that its wheels can, when needed, be locked with a simple piece of masking tape. When the wheels are locked, it skids rather than rolling freely; but its behaviour when skidding depends on which wheels are locked.
    Engagement Suggestion
    • Challenge students to make a prediction about how the car will behave with front or back wheels locked before performing each phase of the experiment.
    • With both sets of wheels free, push the car across the floor; it moves in a straight line with the orientation in which it was pushed.
    • With the front wheels locked and the rear wheels free, it will also continue in the normal forward orientation, slowly skidding to a halt.
    • With the rear wheels locked and the front wheels free, however, when pushed in the forward direction it will rotate so that it moves backward .
    • Students may ask what happens if all four wheels are locked. Encourage them to make predictions based on what they've seen here, and on what other systems the resulting wheelless mass would resemble.
    Background
    Because rolling (static) friction is generally greater than sliding friction, whichever set of wheels is sliding will end up in the forward direction. In real vehicles, this can be the cause of serious accidents!
    C6