Tyas - Vibration & Wave 2011 (2003 verse)

8/7/2019 Tyas - Vibration & Wave 2011 (2003 verse)

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Tyas Ajeng Puspitasari, S.Pd

Grade VIII Semester 2

2010/2011

Junior High School 1 Malang

www. tyas-physics.blogspot.com


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CONTENT

Basic Competency & Indicator

VIBRATION

Displacement and Amplitude

Period and Frequency

Experiment to investigate period of pendulum swing Resonance

Problems of Vibration

WAVE

Kinds of Wave

Transversal and Longitudinal Wave

Calculate Speed of wave

Problems of wave

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Basic Competency Students can plan and do the analysis of data in

the experiment of vibration and waves

1. To identify the movement of vibration with an experiment.

2. To determine the amplitude, period, and frequency of a vibration.

3. To measure period and frequency of vibration

4. Compare the characteristics of transversal and longitudinal waves

5. Investigate the wavelenght on the rope/slinky for transversal and longitudinal

wave.

6. To describe the relation of speed of traveling wave, frequency and wavelength

Objectives:

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Have you ever played a swing?

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Vibration is an oscillatingmovement through apoint of equilibrium

Vibration also known as Simple Harmonic Motion (SHM)

The restoring force also

leads to SHM when theobject is attached to a

vertical spring

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What is a vibration ?


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Now, pay attention to theseat of the swing a boy is

sitting on in figure beside.

When it is not yet moved,

its position is at point O

This point is the

equilibrium

Point of Equilibrium

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Displacement, is any distance between

the vibrating thing and its equilibrium

point.

The maximum displacement of a

vibration is called Amplitude (A)

Displacement and Amplitude

Amplitude (A)

The amplitude of a vibration is

related to the energy of the

vibration. If its amplitude is big, so

its energy is big too.

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One Vibration

B O A

1 vibration =

movement from

A-O-B-O-A.

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B

O

C

O is point of Equilibrium

1 Vibration: C-O-B-O-C

B-O-C-O-B

Vibration: C-O-B

B-O-C

Vibration: C OB O

A is Amplitude

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Vibration of pendulum swing


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Period (T) is the time needed to do one vibration

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Period

n

t

T!

t = time needed (s)

n = number of vibration

The unit of period is second

For example, the time needed for a vibration is 0.5 seconds, so T = 0.5 seconds.


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Frequency (f) the number of vibrations which happens

every second.

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Frequency

t

n

f!

t = time needed (s)

n = number of vibration

The unit of frequency is 1/second or Hertz (Hz)

If the frequency of vibration is 50Hz it means there is any 50 times oscillations

in every second


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Period is inversely proportional withfrequency

The Relation of Period and frequency

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fT

1!

Example:

Calculate the frequency of the vibration of a ruler if its period is 0.02

seconds.

Tf

1

!

Given: T= 0.02 sQuestion:f

Answer: Hzss

f 502

00

02.0!!!!


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1. In 5 seconds, there are 200 times vibration

a. What is the frequency of this vibration?

b. What is the period of this vibration?

2. If the frequency of a vibration is 400 Hz

a. What is the period?

b. How many times the object vibrate for 60 seconds?

3. A pendulum can oscillate 100 times in 10 minutes.

What is the period of the oscillation?

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Problems of Vibration #1


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1. An object vibrates for 40 times in second. The frequency and

the period of the vibration is

2. An object vibrates 50 times in 25 seconds between two points

with a distance of 30 cm

a. What is the frequency of vibration?

b. What is the period of vibration?

c. The amplitude of the vibration is cm

3. If the time needed to move from A to B is 0.05 second

then the number of vibrations in 2 seconds are

4. A pendulum is released from its maximum displacement, after

60 seconds, the pendulum has completed 20 cycles. Calculate

the period and frequency.

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Problems of Vibration #2

B OA


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EXPERIMENT TO INVESTIGATE THE PERIOD OFPENDULUM SWING

OBJECTIVES

To investigate factors that influence period of a pendulum swing.PROBLEM

Is the period of a pendulum influenced by its amplitude?

Is the period of a pendulum influenced by its thread length?

Is the period of a pendulum influenced by its mass?

HYPOTHESIS

*Make hypothesis to estimate the period of a swing if its amplitudeincreases?

MATERIALANDAPPARATUS

a swinging pendulum

a ruler

threada stopwatch or watch

a static upright rod and its clamp

PROCEDURE

*Arrange the steps you will use to examine your hypothesis

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Periodof s ing pendulum is not influenced

y amplitude andpendulums mass

CONCLUSIONFROM THE EXPERIMENT

Periodof s ing is influenced y t readlengt

T e longer t read lengt , t e longer t e

periodof pendulum

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when one object vibrating at the same naturalfrequency of a second object forces that secondobject into vibration motion.

The effect of resonance is in the form of an

increase in the amplitude of its vibration. Without resonance we wouldn't have radio,

television, music, or swings on playgrounds.

Of course, resonance also has its dark side. It

occasionally causes a bridge to collapse, ahelicopter to fly apart, or other inconveniences.

RESONANCE

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Resonance is not always advantageous. In 1831, a suspension bridge in England fell

down because it had resonance with the

trotting shoes of an army marching on it.

In 1940, the Tahoma bridge in USA fell down

because it had resonance with the effect of a

blast of strong wind.

RESONANCE

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When object x swings ,

which pendulum do

you think will swings

too?

RESONANCE

Why????

P

endulumC

!!

The pendulums swing with the same

frequency

Frequency of pendulum is depend on theirthread length and gravitational acceleration

So, pendulum with the same thread length

with the swinging object will swings too


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Wave

Awave is a disturbance travelling withdefinite energy from one place to another

You can make a wave on a rope.

In this case, the rope is called amedium


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When the disturbance moves through the medium,

the particles of the medium only move up and

down (or closer and farther apart).

Do the particles of the medium follow the movement of

the wave?

While moving, the wave does not

carry particles of the medium

A wave carries ENERGY from one

place to another.

so, what is carried

by a wave?


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Wave

Mechanic Wave

RequireMedium

Example:

Ocean waves, seismic waves,sound waves

Electromagnetic Wave

needs no mediumto travelling

Example:Light, Radio waves, X-rays

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Rarefaction

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Kindof ave

Transverse Wave

The direction of its vibration is perpendicular to the

movement direction of wave

Longitudinal Wave

The direction of its vibration is parallel to the movementdirection of wave


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Transverse Wave

The movement directionof wave is perpendicular

to the direction of its

vibration

Example: Light, Water

wave, Ropes wave

A wavelength () is the distance between one point in a wave

and the nearest similar point in the wave.

Example: the distance from a crest to the nearest crest or from

a trough to trough

Large amplitude Large energy carried by wave

Small amplitude Small energy carried by wave

crest


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Longitudinal Wave

The movement directionof wave is parallel to the

direction of its vibration

Example: Sound

A wavelength () is the distance between the two nearest

rarefactions or two nearest compressions.


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Speed of wave

Remember

t

sv ! If the wave passes one wavelength (), itspassing time is the period of the wave (T),

and the previous formula can be rewritten as

Tv P

Relation offand T is:

Tf

1!

fv .P

v= speed of wave (m/s) = wavelength (m)

T= period (s)

f= frequency (Hz)


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EXERCISE OF WAVE #1

1. From the figure of wave beside, find itsa. Amplitude

b. wavelength

c. Period 15 m

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t (seconds)30

cm

2. Calculate the speed of the following wave

3. Calculate the speed of the following wave2seconds

3 m


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2. To find speed , there are two ways:

Or find its wavelength and period first.

Then find the speed with formula:

Two variations way give the same result, that speed is equal to 4 m/s

1.

a. Amplitude = 15 cm

b. Wavelength :

c. Period

ANSWER

mmwaveofnumberropeoflength 10

5.1

15 !!!P

ss

waveofnumber

timetotalT 4

5

6!!!

sm

timetotal

lengthtotal4

6

24!!!P

m842 !v!Ps

sT 2

3

6!!

sTv 4

2

8!!!

P

3. From the picture, we already know the T = 2 seconds (distance between crestto crest)

Then find its wavelength

Thus its speed:

m

m

wa

o

numbr

ropo

ng

h2

5

3!!!P

sTv 1!!!

P

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Tyas - Vibration & Wave 2011 (2003 verse)

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Transcript of Tyas - Vibration & Wave 2011 (2003 verse)