Exp SPA Chp 12 General Wave Properties

WAVES

a) describe what is meant by wave motion as illustrated by vibrations in ropes and springs and by waves in a ripple tank

b) show understanding that waves transfer energy without transferring matter

c) compare transverse and longitudinal waves and give suitable examples of each

LEARNING OBJECTIVES

How does a Kallang Wave look like?

The Kallang wave moves around the stadium, but the people do not.

How do people move in a Kallang Wave?

KALLANG WAVE

A wave is a disturbance that transfers energy from one place to another.

It is made up of periodic motions – motion repeated at regular intervals.

We can also call it periodic oscillations. (recall pendulum)

INTRODUCING WAVES

1. Kinetic energy from the moving hand is transferred to the rope.

2. This forms a rope wave (a wave that travels within the rope).

3. The rope wave moves from the hand to the wall ( left to right).

4. As the wave moves through the rope, from left to right, the rope particles (P and Q) move up and down , about their rest positions.

5. Eventually, the kinetic energy is transferred from the hand to the wall.

INTRODUCING WAVESWAVES IN A ROPE

Kinetic energy from the dipper is transferred to the water.

This forms a water wave (i.e. a

water ripple).

The water wave moves outwards from the dipper.

The water particles move up and down, about their rest positions.

In other words, the kinetic energy gets transferred from the dipper to the edges of the ripple tank.

INTRODUCING WAVESWAVES IN A RIPPLE TANK

The source of a wave is a vibration or an oscillation.

Waves transfer energy from one point to another.

Waves transfer energy without transferring the medium (i.e. rope or water).In another words, the particles do not move forward with the wave.

INTRODUCING WAVESSUMMARY

Observe how I move the spring. Describe the motion of the spring.

If we move the spring in an up-down motion:

The spring coils move perpendicular to the direction of the wave.

INTRODUCING WAVESWAVES IN A SPRING

(top view)up

down

Wave direction

If we move the spring in a push-and-pull motion:

The spring coils move parallel to the direction of the wave.

INTRODUCING WAVESWAVES IN A SPRING

Wave direction

From the Slinky Spring, we can see that there are 2 types of waves.Transverse wavesLongitudinal waves

INTRODUCING WAVESTYPES OF WAVE MOTION

How do transverse waves differ from longitudinal waves?

The coils move up and down, while the wave moves from left to right.

The movement of the coils is perpendicular to the wave motion.

E.g. Electromagnetic waves i.e. light, infrared-red, ultraviolet

INTRODUCING WAVES TRANSVERSE WAVES

Transverse waves are waves that travel perpendicular to the direction of the medium’s particle vibration.

The coils move left and right, while the wave moves from left to right.

The movement of the coils is parallel to the wave motion.

Examples: Sound waves

INTRODUCING WAVESLONGITUDINAL WAVES

Longitudinal waves are waves that travel parallel to the direction of the medium’s particle vibration.

In longitudinal waves, the part where the particles of matter are close together is called the compression.

The part where the particles are spread apart is called the rarefaction.

Longitudinal waves are formed by a series of compression and rarefactions.

INTRODUCING WAVESLONGITUDINAL WAVES

Describe and explain the motion of the Styrofoam balls (if any) when the rod is dipped quickly into the water and then removed.

INTRODUCING WAVES

rod

water

Styrofoam balls

Is the wave formed transverse or longitudinal?

INTRODUCING WAVES

rod

water

Styrofoam balls

What is a wave?

2 kinds of waves Transverse – particles move perpendicular to wave motion Longitudinal – particles move parallel to wave motion

SUMMARY

a) define speed, frequency, wavelength, period and amplitude

b) state what is meant by the term wavefrontc) Recall and apply the relationship velocity =

frequency × wavelength to new situations or to solve related problems

LEARNING OBJECTIVES

When describing a wave, there are a lot of scientific terms.

Therefore we want to understand what does each term means.

PROPERTIES OF WAVE MOTION

When water waves are produced, the peaks of the waves forms a circle and move outwards from the sources of disturbance.

DefinitionWavefront is the line that

joins all the peaks of a wave or all identical points on a wave.

PROPERTIES OF WAVE MOTIONDESCRIBING WAVES

Plane waves can be produced by disturbing the water surface with a vibrating wooden bar.

The wavefronts of plane wave are straight lines that moves away from the source of disturbance.


Crests – the highest point of a transverse waveTroughs – the lowest point of a transverse

wave

Which of the points labelled on the wave are crests and which are troughs??


P

Q

R

S

T

U

V


The amplitude A of a wave is the maximum possible displacement of a point from its rest position.

P

Q

R

S

T

U

V

amplitude (height of crest)

amplitude (depth of trough)


Points along a wave are in phase if they have the same• direction;• speed;• displacement from their rest positions.

P

Q

R

S

T

U

VQuestionWhich points on the wave are in phase?

1. P, S, V2. Q, T3. R, U


The wavelength l of a wave is the shortest distance between any two points in phase.

P

Q

R

S

T

U

Vwavelength

wavelength

wavelength


The frequency, f, is the number of complete waves produced per second.

SI Unit of frequency is the hertz (Hz).

SI Unit of period is the seconds (s).

The period, T, is the time taken to produce one complete wave.


Looking at the ripple tank.

Frequency Period

5 waves produced in 1 second.

𝐅𝐫𝐞𝐪𝐮𝐞𝐧𝐜𝐲 , 𝒇=𝟓𝑯𝒛 𝐏𝐞𝐫𝐢𝐨𝐝 ,𝐓=𝟏𝒇

=𝟏𝟓

=𝟎 .𝟐𝐬


In one period, what is the distance moved by a wave crest? The wave moves by 1 wavelength.

Therefore is the formula for speed of waves.

Wave speed v is the distance travelled by a wave per second.

PROPERTIES OF WAVE MOTIONDISPLACEMENT-DISTANCE GRAPH

A picture capture of the wave motion at a specific time, for e.g. at t = 0 s.

From the displacement-distance graph, we can find the amplitude, A and wavelength, l of the wave.

P

Q

R

S

T

U

V

PROPERTIES OF WAVE MOTIONDISPLACEMENT-TIME GRAPH

Follow 1 particle on the wave, say ribbon Q.

We then used the information to plot the displacement of ribbon Q over a period of time.

P

Q

R

S

T

U

V

PROPERTIES OF WAVE MOTIONDISPLACEMENT-TIME GRAPH

From this graph, we can find the amplitude, A and period, T of the wave.

Wave Terms: Wavefront Amplitude Wavelength Frequency Period Wave speed

Wave graphs Displacement-distance graph Displacement-time graph

SUMMARY

A wave in a string is travelling to the right at 2 m s –1. The diagram below shows its displacement–distance graph at t = 0 s.

a) Sketch the graph to show how the wave will appear at t = 3 s.

b) Draw and label the position of P and Q at t = 3 s.

PRACTICE QUESTION 1

Displacement/m

Distance/m

P

82 4 6

Q

Solution

PRACTICE QUESTION 1

x/m

d/mP

t = 3 s

x/m

d/m

P

82 4 6

Q

Q

t = 0 s

A wave in a string is travelling to the right at 2 m s –1. The diagram below shows its displacement–distance graph at t = 0 s.

Plot a graph to show how the displacements of particles P and Q vary with time.

PRACTICE QUESTION 2

Displacement/m

Distance/m

P

82 4 6Q

Solution

PRACTICE QUESTION 2

Displacement/mP

Time/sQ421 3

Education

Exp SPA Chp 12 General Wave Properties