Physics Unit 4 Notes

Unit 4 Physics Notes
Sunday, November 3, 2013

8:09 PM

Any Single disturbance is called a pulse
A series of pulses is called a wave

In the case of the impatient student, his disturbance was parallel to the direction of the wave itself. Also called a Longitudinal Wave

WAVES
• Waves can transmit two things
○ Can transmit energy
 Ex. Light waves from the sun heat the earth
○ Can transmit information
 Ex. Radio wave

When the motion of the particles is perpendicular to the motion of the wave, it is called a traverse wave
Pointing down
Acceleration down

Wave -> We see the motion of the medium
Soundwaves -> air
Lightwaves = electromagnetic waves
Stadium waves -> people
Water waves -> water
Light waves -> no medium
Pointing up
Acceleration up

Without tension, there can be no traverse waves in a medium.
-> Do not occur inside liquids and gases -> can occur on surface of water though

Inner core of earth has a liquid core, because traverse waves do not got through
Earthquakes can produce traverse, longitudinal, or a combination of the two.
-> longitudinal = compression, travel fast, primary (happen first)
-> traverse = "__________ waves", secondary (happen second)
-> longer delay between S and P waves, means greater distance from the epicenter

A)
B)
C)
D)

Crest
Trough
Amplitude
Wavelenght
Cycle -> one complete wavelength
Amplitude -> half the distance from crest and trough
Wavelength -> distance of one complete cycle (SI units = meters)
Period (T) -> time for one wavelength to pass (SI Units = seconds)
Frequency (f) -> number of cycles that pass by per time interval
= Cycles per second = 1 Hertz (Hz)
T=(1/f) and f=(1/T)
Ex. f=2 Hz = T=.5 seconds

Swing?

Applied force at a regular interval, causes you to go higher, high amplitude

All object will vibrate of oscillate at a certain frequency called the natural frequency
A pendulum (or swing) will swing back and forth at a natural frequency that depends only on it's lenght When a system is driven at it's natural frequency (forces applied in rhythm with the natural frequency),
Physics Unit 4 Page 1

The shorter the stick, the higher the
Natural frequency.

When a system is driven at it's natural frequency (forces applied in rhythm with the natural frequency), the oscillations will get bigger. This s termed resonance.

If two things have the same natural frequency,
And you hit one, the second will also begin to vibrate

Energy
Transfer

Unequal natural frequency, then vibrations won't transfer

It is possible for an object to have more than one natural (resonant) frequency. Natural frequency is the 1st harmonic
Other harmonics can be produced as well

If the displacement is one wavelength, then the time equals a period (T).
Wave Speed (or Velocity)
Wave Velocity

Velocity = Displacement/time = d/t

F = 1/T
T = 1/f

V = ʎ (wave length) / T (Period)
V = fʎ

Ex. Distance between waves is 6m, and one wave takes 4 seconds.
T=4
F = 1/4 Hz
V = (1/4) x 6m = 1.5 m/s

Ex.
1st

2nd

3rd

Aver.

Speed

10cm

1.3

1.5

1.5

1.4

5.7m/s

30cm

1.5

1.3

1.7

1.5

5.3m/s

50cm

Transverse

Amp

1.6

1.4

1.5

1.5

5.3m/s

Compression

Amplitude = amount of energy being transmitted Energy effects amplitude, not speed

ʎ

T1

T2

T3

Aver.

Speed

8

1.3

1.4

1.5

1.4

5.7m/s

14

.72

.74

.74

.73

5.4m/s

2.67

.40

.46

.50

.48

5.0m/s

What factors affect the speed of the wave?
Amplitude = no
Wave Length = no
Only the properties of the medium affect the wave speed

When waves meet, their amplitudes add (called the principle of superposition). After they meet, they pass through each other. Each wave in no way alters the travel of the other.

Physics Unit 4 Page 2

Amplitude of the wave has
NO EFFECT on the speed of it

Effect of different wave length on speed of wave
= NO EFFECT