ch18 - oscillations

Question 1

oscillation

Answer 1

a repetitive back-and-forth or up-and-down motion

Question 2

types of oscillations

Answer 2

. free
. forced

Question 3

free oscillations

Answer 3

. when an object moves at its natural frequency
. no energy constantly added

Question 4

forced oscillations

Answer 4

. body is forced to vibrate due to the oscillation of some other object
. not at natural frequency

Question 5

natural frequency

Answer 5

the frequency at which a body vibrates when there is no resultant external resisitive force acting on it

Question 6

eyes can only see oscillations of frequency less than

Answer 6

5 Hz

Question 7

ways of observing oscillations

Answer 7

MASS-SPRING SYSTEMj
. trolley with two springs
. oscillating between two clamps

LONG PENDULUM
. mass on pendulum will swing back and forth

LOUDSPEAKER CONE
. signal generator makes loudspeaker vibrate
. electronic stroboscope to show cone movement

Question 8

sinusoidal

Answer 8

having a magnitude that varies in the form of a sine curve

Question 9

amplitude, xo

Answer 9

the maximum displacemegbmt of a particle from its equilibrium position

maximum displacement of a wave

Question 10

period

Answer 10

time taken to make one complete oscillation

Question 11

frequency

Answer 11

1/T

Question 12

phase

Answer 12

the point that an oscillating particle has reached within the complete cycle of an oscillation

Question 13

phase difference

Answer 13

the difference in the phases of two oscillating particles measured in degree or radians

Question 14

simple harmonic motion (shm)

Answer 14

a body executes simple harmonic motion if its acceleration is directly proportional to its displacement from its equilibrium position, and in opposite direction to its displacement

Question 15

shm situations

Answer 15

. when a pure sound wave travels through air, the air molecules vibrate with shm

. when ac flows in wire, the elctrons in the wire vibrate with shm

. there is a small ac in radio or tv when it is tuned to a signal in the form of electrons moving with shm

. atoms that make a molecule vibrate with shm

Question 16

shm requirement

Answer 16

. mass that oscillates
. position where the mass is in equilibrium
. a restoring force that acts to return the mass to its equilibrium position

F proportional to x

Question 17

velocity in shm

Answer 17

if on left side:

acceleration till center
max v at center
deceleration till right

repeat with negative velocity

Question 18

displacement-time graph

Answer 18

. motion sensor with oscillating object
. ultrasonic pulses from sensor are reflected by the card on the trolley
. reflected pulses detected
. graph shown on screen display

Question 19

graphs of shm

Answer 19

X-T GRAPH
. amplitude and T can be found
. sinusoidal

V-T GRAPH
. cosine type graph

A-T GRAPH
. sine graph starting in negative

Question 20

a is proportional to - x

Question 21

angular frequency

Answer 21

the frequency of a sinusoidal oscillation expressed in radians per second

Question 22

angular frequency (w)

Answer 22

w = 2pi f

Question 23

w = 2 pi/ T

Question 24

equations of shm

Answer 24

x = x0 * sinwt
x = x0 * coswt

Question 25

difference between sine and cosine funtion of shm

Answer 25

sine: . starts at x = 0 cosine: . starts at x = x0

Question 26

a = - w²x

Answer 26

acceleration of an object vibrating in shm

Question 27

a-x graph for a graph for an oscillator executing shm

Answer 27

. straight line through origin . negative slope (minus sign) . gradient magnitude = w² gradient independent of amplitude

Question 28

x = x0 * cos wt

Question 29

v = ±w square root (x0² - x²)

Answer 29

speed oscillator

Question 30

in cos graph

Answer 30

v0 = w x0

Question 31

to find max speed

Answer 31

v0 = (2 pi f) x0

Question 32

energy exchange between which two forms in shm

Answer 32

potential, kinetic

Question 33

if potential energy increases

Answer 33

kinetic energy decreases

Question 34

max potential energy where?

Answer 34

at sides

Question 35

max kinetic energy where?

Answer 35

at centre

Question 36

total energy in system is constant, provided

Answer 36

oscillations are undamped

Question 37

total energy of system undergoing shm

Answer 37

E0 = 0.5mv² v0 = wx0 E0 = 0.5mw² x0²

Question 38

damped

Answer 38

a damped oscillation is an oscillation in which resistive forces causes the energy of the system to be transferred to the surroundings as internal energy DECREASING AMPLITUDE SAME FREQUENCY

Question 39

damping used

Answer 39

to reduce oscillations

Question 40

resonance

Answer 40

a term used when a system oscillates with maximum amplitude by absorbing energy from a vibrating source

Question 41

when does resonance occur

Answer 41

driving force frequency = natural frequency of oscillating system

Question 42

observing resonance in lab

Answer 42

BARTON'S PENDULUMS . multiple pendlums of different length . one same length as driver pendulum will have increasing amplitude, and resonate MASS-SPRING SYSTEM . move hand at same speed as ball's bounce on spring

Question 43

to a system in resonance

Answer 43

. natural frequency = frequency of driver . amplitude is maxium . absorbs greatest possible energy from the driver

Question 44

how to reduce damaging effects of resonance

Answer 44

more damping = amplitude decreases less

Question 45

critical damping

Answer 45

the minimum damping that causes the oscillating system to return to its equilibrium position in the minimum time and without oscillating lighter = more oscillation heavier = more time

Question 46

using resonance

Answer 46

. musical instruments . microwaves - water molecule vibration, absorb microwave ratiation . MRI scanners - radio waves and atomic nuclei . radio/TV - tuner resonates only at wanted frequency