PHYS16 – Lecture 37 Ch. 16 Wave Motion “Interference is much clearer in HD”

Oscillations pre-question Is a bouncing ball an example of simple harmonic motion? A)Yes B)No

Oscillations pre-question Two kids are swinging on two swings of the same height – one kid is a little chubbier than the other. Neglecting frictional forces, which kid completes a back and forth swing in the fastest time? A) The chubby kid B) The skinny kid C) The kid who pushes off the ground the best D) Both complete in the same time

Oscillations pre-question A mass on a spring is driven at a driving frequency (red curve) and the resulting position vs. time of the mass is given (blue curve). Which case is closest to resonance?

Ch. 16 Wave Motion Mechanical Waves – Transverse vs. Longitudinal – Properties Example: Wave on a String – How the wave propagates – Speed – Reflection and Transmission Superposition and Standing Waves

Waves pre-question PhET website

Waves pre-question PhET website

Mechanical Waves

A propagating oscillation that moves through a medium Transverse – water waves, disturbance on a string Longitudinal – sound waves, slinky or spring

Mechanical Waves Waves use at least 1-3 space dimensions and time… – Ex. – Water waves propagate in x, move “up and down” in y, and change position with time – Ex. – Sound waves propagate in x, move “up and down” in x, and change position with time

Wave Properties Period – T high period medium period low period

Wave Properties Period – Wavelength and Wave number –

Wave Properties Period – Wavelength and Wave number –

Wave Properties Period – Wavelength and Wave number – Wave speed –

Ripple Tank Simulation

Example: Speaker PhET website Speed = Period = Wave number = Wavelength = 330 m/s s 5.0m m

Example: Sand on a vibrating plate Sand is placed on the vibrating plate below. Which apparatus is vibrating the plate with the highest wave number?

Wave Function or Waveform Plane Wave Higher Dimension Wave

Wave on a String

You can generate a wave on a string by pulsing sting with your hand Speed of pulse/wave is related to tension in string and mass density of string PhET website

Propagation of Pulse If you advance the movie one frame point A will move… (higher, lower, right, left)? If generate new pulse but more quickly than first then it will be… (same, wider, narrower)? If generate new pulse but move hand higher than first then it will be… (same, taller, shorter)? If generate new pulse with rope tightened then pulse will be… (same, faster, slower)? PhET website

Wave on String Simulation PhET website

Example Question PhET website

Superposition, Interference, and Standing Waves

Main Points – Wave Properties Mechanical Wave – a propagating oscillation that moves through a medium Period – Wavelength and Wave number – Wave speed –