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Newton's Second Law

  • C4-53 WEIGHTLESSNESS IN FREE FALL - MASS ON SPRING

    C4-53
    Illustrate apparent weightlessness in free fall
    When suspended by the end opposite the mass, the spring extends because of the weight of the mass attached. However, when the spring is released and allowed to fall freely, the system becomes weightless and the spring immediately contracts.
    C4

  • C4-54: WEIGHTLESSNESS IN FREE FALL - MAGNET AND KEEPER

    C4-54
    Illustrate weightlessness in free fall.
    The keeper is placed on an aluminum shelf about two centimeters below the "C" magnet; the gravitational force on the keeper is sufficient to keep it from being attracted to the magnet. When the system is released and allowed to fall with the acceleration of gravity, the keeper becomes weightless and is attracted to the magnet

  • 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.

  • C4-62 DROPPED SLINKY

    C4-62
    Illustrate apparent weightlessness in free fall
    A SLINKY is suspended from one end and released from rest. The bottom end will remain at rest until the entire SLINKY has collapsed, at which time it will begin to accelerate downward.
    C4

  • D1-44: ACCELEROMETERS AND FRAMES OF REFERENCE

    D1-44
    Demonstrate the direction of the acceleration in both rotational and translational coordinate systems
    In each experiment the ping-pong balls act as accelerometers. When the jars are rotated, the ball suspended from the bottom of the water-filled jar moves toward the direction of the acceleration, while the ball suspended from the top of the air-filled jar moves in the direction opposite the acceleration. The ping-pong ball in the water-filled tube indicates the direction of the acceleration when the tube is accelerated linearly or rotated.

  • D2-31 OBERBECK CROSS

    D2-31
    Illustrates rotational analog of Newton's second law of motion
    Various masses M can be hung on a string wound around an axle of either of two radii R to provide a torque T = MgR. Four brass masses m can be positioned along the arms at one of four distances l from the axis of rotation to provide a moment of inertia I = 4ml^2. The angular acceleration a = T/I = MgR/4ml^2 can then be calculated. The angular acceleration can be determined experimentally by measuring the time required for the system to rotate one complete revolution starting from rest: a = 2 d/t^2, where t is the time required for the device to rotate through the angle d in radians.
    FS1

  • G1-18: PENDULUM WITH FORCE SCALE

    G1-18
    Show the tension in the string exerted by a swinging pendulum.
    The spring scale reads the tension in the string as the pendulum swings, about 25 Newtons at the center and 19 Newtons at the ends of the swing with a bob mass of 1.1 kG. In this setup: F (center) = mg + mrw^2 = mg (3 - 2 cos a) F(end) = mg cos a where by conservation of energy m v^2 /2 = m r^2 w^2 /2 = mgr (1 - cos a) m r w^2 = 2mg ( 1 - cos a)

  • G1-36: MASS ON SPRING WITH FORCE MEASUREMENT

    G1-36
    Display the time dependence of the force of a mass oscillating on a spring.
    A mass hangs on a spring that is in turn hanging from a spring scale. When the mass is raised and released, executing SHM, the force as a function of time (or position of the mass) is displayed by the spring scale.
    FS1

  • I2-42: FALLING CANDLE

    I2-42
    Demonstrate how a flame burns in the absence of normal convection.
    A candle, attached to the lid of a one-gallon jug, is lit and the lid screwed onto the upside-down jug. Throw the upside-down jug into the air and catch it or hold the upside-down jug high and drop it and catch it as it falls. While it is falling, the system inside the jar is in a weightless environment, so convection currents cease. In normal burning, the hot air rises by convection, allowing cooler air containing more oxygen to continuously feed the fire. Without these convection currents the candle should immediately go out, BUT IT DOES NOT.
    I2

    A candle mounted on the lid of a gallon jug is lit, and the lid quickly affixed to the jug. In this configuration the candle will remain lit for over one minute before the oxygen in the jug is sufficiently used up by the combustion process and the flame is extinguished.

    Now suppose that the candle flame is lit and the lid again quickly affixed to the jug. However, the bottle is now dropped about six feet starting from the orientation shown in the photograph below.

    i2 42

    What will happen? In particular, by the time the jug falls six feet the candle flame will:

    • (a) burn more brightly.(b) remain at about the same brightness.
    • (c) burn less brightly.
    • (d) go out.