25.1 – vibrations of a pendulum

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25.1 – vibrations of a pendulum - PowerPoint PPT Presentation

25.1 – vibrations of a pendulum. Period of oscillation only depends upon: Length of pendulum Acceleration of gravity Independent of mass Shorter = swings more often = higher frequency Example of simple harmonic motion (SHM). Masses on springs (honors). Masses on spring also exhibit SHM

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Presentation Transcript
25.1 – vibrations of a pendulum
• Period of oscillation only depends upon:
• Length of pendulum
• Acceleration of gravity
• Independent of mass
• Shorter = swings more often = higher frequency
• Example of simple harmonic motion (SHM)
Masses on springs (honors)
• Masses on spring also exhibit SHM
• Restoring force α distance from equilibrium
• Bigger k = stiffer spring
• Oscillating spring systems only depend upon:
• Mass at end of spring
• Spring constant
25.2 – wave description
• Vibrations are what produces waves
• Looks like a sine wave
• # of cycles (vibrations) per second = frequency (f)
• Unit: s-1 = hertz (Hz)
• Period (T) = time for 1 cycle
25.3 – wave motion
• Waves transfer energy not matter
• Only temporary motion of matter
• No matter is transmitted between 2 points
• The matter “bangs” into matter next to it, giving it energy
25.4 – wave speed
• Depends upon medium
• Can be calculated as the distance a crests moves in a certain time
• Fundamental relationship between: speed, wavelength & frequency
• For the same type of wave – speed is the same
• λ & f are inverses of one another
25.5 & 25.6 – transverse & longitudinal waves
• Wave pulse is perpendicular (across) from the direction of travel
• EM waves need no medium to travel
• Oscillation is back and forth in the direction of wave travel
• Sound waves
Electromagnetic waves
• A self propagation of E & B fields
• As one changes, so must the other
• Moves at the speed of light, c = 3.00 x 108 m/s
• Caused because of accelerating electric charges

Vibrations determine the frequency of EM waves

• Visible light is just a sliver of EM spectrum
• Includes: radio waves, microwaves, infrared, visible, ultraviolet, x-rays, gamma rays
• In order of increasing energy
25.7 - interference
• When waves meet and overlap
• Constructive interference
• Waves meet & amplitude gets larger
• Destructive interference
• Amplitude gets smaller
• When wave crests exactly line up – in phase
• Not common
• Out of phase when crest & trough overlap
• Creates dark bands
25.8 – standing waves
• Waves generated have locations that appear to not move
• Parts of wave that appear stationary – nodes
• Complete destructive interference
• Next to these are locations of maximum amplitude – antinodes – constructive int.
• As waves meet, they interfere and then pass through one another
• Higher frequency generate more standing waves
25.9 – doppler effect
• The apparent change in frequency due to motion of source or observer
• Waves move in all directions at same speed
• Source moving “bunches up” waves in direction of motion & “spreads out” behind
• Occurs for all waves – sound & light
• Blue shift – object towards us
• Red shift - away
25.10 – bow waves
• Bow waves occur when wave source moves faster than the waves produced
25.11 – shock waves
• Shock waves are produced when object is faster than speed of sound
• Caused because of constructive interference
• Creates a conical shell of compressed air
• This is the sonic boom
• Always carried with plane (object) going ≥ vsound