Finding Mass of an Astronaut in Space

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Finding Mass of an Astronaut in Space
This device consists of a spring-mounted chair in
which the astronaut sits. The chair is then
started oscillating in simple harmonic motion.
The period of the motion is measured
electronically and is automatically converted
into a value of the astronauts mass, after the
mass of the chair is taken into account. The
spring used in one such device has a spring
constant of 606 N/m, and the mass of the chair is
12.0 kg. The measured oscillation period is 2.41
s. Find the mass of the astronaut. (students work
this.)
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Mass of an Astronaut
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Example 1 The Wavelengths of Radio Waves AM and
FM radio waves are transverse waves consisting of
electric and magnetic field disturbances
traveling at a speed of 3.00x108m/s. (What is
this number?) A station broadcasts AM radio waves
whose frequency is 1230x103Hz and an FM radio
wave whose frequency is 91.9x106Hz. Find the
distance between adjacent crests in each wave.
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16.2 Periodic Waves
Example 1 The Wavelengths of Radio Waves AM and
FM radio waves are transverse waves consisting of
electric and magnetic field disturbances
traveling at a speed of 3.00x108m/s. A
station broadcasts AM radio waves whose frequency
is 1230x103Hz and an FM radio wave whose
frequency is 91.9x106Hz. Find the distance
between adjacent crests in each wave.
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16.2 Periodic Waves
AM
FM
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Problem

• Light travels at 3 10 8 m/s. Sound travels at
  331 m/s.
• If lightning strikes 8.2km away from you, how
  long passes before you see it?
• How long passes until you hear it?
• (students work this.)

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Problem

• Light travels at 3 10 8 m/s. Sound travels at
  331 m/s.
• V d/t gt t d/v
• If lightning strikes 8.2km away from you, how
  long passes before you see it?
• t d/v 8200m / 3 10 8 m/s
• How long passes until you hear it?
• t d/v 8200m / 331 m/s
• (students work this.)

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Problem

• So you see lightning hit 1 mile away, how many
  seconds do you count before you hear it?
• (students work this.)

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Problem

• So you see lightning hit 1 mile away, how many
  seconds do you count before you hear it?
• t d/v 1609m / 331 m/s
• So each 5 sec is about 1 mile away.
• Each 1 sec is about 3 football fields away.
• (Talk about military timing of artillery and
  nukes.)

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THE PRINCIPLE OF LINEAR SUPERPOSITION When two
or more waves are present simultaneously at the
same place, the resultant disturbance is the sum
of the disturbances from the individual waves.
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Constructive Interference

• Two waves, a and b, have the same frequency and
  amplitude
• Are in phase
• The combined wave, c, has the same frequency and
  a greater amplitude

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Destructive Interference

• Two waves, a and b, have the same amplitude and
  frequency
• They are half a cycle out of phase
• When they combine, the waveforms cancel

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Reflection of Waves Fixed End

• Whenever a traveling wave reaches a boundary,
  some or all of the wave is reflected

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Reflection of Waves Fixed End

• Whenever a traveling wave reaches a boundary,
  some or all of the wave is reflected
• When it is reflected from a fixed end, the wave
  is inverted
• The shape remains the same

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What happens when a wave interferes with its own
reflection?

• Sometimes we get standing waves.

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1st Harmonic
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2nd Harmonic
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3rd Harmonic
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• The a string will only allow certain wavelengths
  to be standing waves.
• Because the endpoints need to be nodes.
• For a string with two fixed ends,
• ? 2L / n n 1, 2, 3, 4 .