Harvard Natural Sciences Lecture Demonstrations
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  • Pendulum Waves

    10,591,458 views 8 years ago
    Fifteen uncoupled simple pendulums of monotonically increasing lengths dance together to produce visual traveling waves, standing waves, beating, and (seemingly) random motion.

    For more details see http://sciencedemonstration......

    The period of one complete cycle of the dance is 60 seconds. The length of the longest pendulum has been adjusted so that it executes 51 oscillations in this 60 second period. The length of each successive shorter pendulum is carefully adjusted so that it executes one additional oscillation in this period. Thus, the 15th pendulum (shortest) undergoes 65 oscillations.

    Our apparatus was built from a design published by Richard Berg [Am J Phys 59(2), 186-187 (1991)] at the University of Maryland. The particular apparatus shown here was built by our own Nils Sorensen.

    Video courtesy of Harvard Natural Sciences Lecture Demonstrations, © 2010 President and Fellows of Harvard College Show less
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    • Visualizing Ultrasound with Schlieren Optics Part III - Duration: 5 minutes, 59 seconds.

      • 8 months ago
      • 4,510 views
      Part 3 of 3. We combine the stroboscopic effect with the use of color filters in our schlieren optics setup to visualize the changes in air pressure that occur in a standing wave created by an ultr...
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    • Visualizing Ultrasound with Schlieren Optics Part II - Duration: 2 minutes, 57 seconds.

      • 8 months ago
      • 2,218 views
      Part 2 of 3. We use our strobing schlieren system to look at diffraction and standing wave patterns in air created by an ultrasonic transducer (driven at 28 kHz) and a reflecting glass plate.

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    • Visualizing Ultrasound with Schlieren Optics Part I - Duration: 4 minutes, 59 seconds.

      • 8 months ago
      • 6,261 views
      Part 1 of 3. We use a schlieren optics system with a strobing light source to visualize ultrasonic waves emitted by a transducer driven at a frequency of 28 kHz.

      Images employing schlieren optics ...
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    • Coanda Effect - Duration: 3 minutes, 49 seconds.

      • 1 year ago
      • 79,793 views
      Fluids flowing near a surface tend to follow the shape of the surface. Using Schlieren optics, we can see this behavior. It is known as the Coanda Effect and its explanation depends on viscosity, ...
    • Ultrasonic Levitation - Duration: 4 minutes, 34 seconds.

      • 2 years ago
      • 508,154 views
      Acoustic levitation meets Schlieren optics: By reflecting a sound wave back onto itself, one can secure a standing wave if the distance between the source of the sound and the reflector is equal to...
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    • Fire Tornado - Duration: 2 minutes, 12 seconds.

      • 2 years ago
      • 2,424 views
      A story of one man's love of a fire tornado demonstration. A small metal container sits in the center of a 13" diameter turntable. Bending and clamping a brass screen (10 wires per inch) around the...
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    • Vacuum Cannon - Duration: 40 seconds.

      • 2 years ago
      • 5,360 views
      High speed footage of a ping pong ball, propelled by air rushing into an evacuated tube, penetrating three empty soda cans. The PVC tube is 8 feet long and 1.5 inches in diameter, with a layer of m...
    • Sodium Absorption Lines - Duration: 85 seconds.

      • 2 years ago
      • 31,168 views
      Burning of sodium bicarbonate in Bunsen flame produces sodium absorption lines in continuous spectrum. Sodium 'D' line absorption shows up as a black line in the yellow of a continuous spectrum. Go...
    • Reverse Sprinkler - Duration: 94 seconds.

      • 3 years ago
      • 6,175 views
      Which direction does a lawn sprinkler spin if fluid enters the nozzle rather than being expelled from it? Inspired by Richard Feynman's story in his 1985 book "Surely You're Joking, Mr. Feynman."

      ...
    • Meissner Effect - Duration: 2 minutes, 46 seconds.

      • 3 years ago
      • 19,993 views
      A permanent magnet begins to hover above a ceramic material as it cools and transitions to a superconducting state; the magnet remains aloft until the ceramic warms above a critical temperature.

      T...
    • Mousetrap Fission Setup - Duration: 52 seconds.

      • 3 years ago
      • 3,799 views
      Woflgang and Allen quickly and efficiently prepare the Mousetrap Fission demo for Robert Kirshner's The Energetic Universe course on February 26, 2015. The demo consists of 110 mousetraps armed wit...
    • Thin Film Interference (part 2) - Duration: 2 minutes, 59 seconds.

      • 4 years ago
      • 14,699 views
      Close up of a thin film of soapy water that is vertically suspended across a 19 cm diameter plastic ring and illuminated with white light. Gravity pulls down on the film to make it much thinner in ...
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  • Newtonian Mechanics Play all

    Laws of Motion, Momentum, Rotational Dynamics
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  • Fluids Play all

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  • Oscillations and Waves Play all

    Simple Harmonic Motion, Resonance
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