A2 Physics

Front 1

how do geostationary satellites work?

Back 1

satellite dishes focus em waves carrying a television signal onto an aerial

Front 2

a geostationary satellite must

Back 2

have its orbit centred on the centre of the Earth

be travelling from west to east

be over the equator

have a period of 24 hours

Front 3

geostationary satellites are used for:

Back 3

telecommunications; television broadcasting

Front 4

problems with geostationary satellites

Back 4

very costly; requires a large gain in kinetic and potential energy to put into orbit.

very large footprint as they need to transmit at high power (long way from Earth)

Front 5

advantages of geostationary satellites

Back 5

as there is a large footprint for any satellite, there is a large area of houses can receive the signal

Front 6

low-level satellites

Back 6

not geostationary

usually at heights up to 500km

transmissions only received by tracking receivers

many are needed for complete earth coverage (as they are always moving)

Front 7

advantages of low level satellites

Back 7

less expensive to put them into orbit (less energy required)

greater detail about the Earth can be seen on any photos they take

higher intensity (power per unit area) achieved on the Earth's surface

Front 8

uses of low level satellites

Back 8

weather satellites (european meteosat provides weather detail such as temperature, pressure, humidity and wind speed)

spy satellites (movement of people can be monitored when outdoors)

mapping (effect of humans on the environment can be seen, such as deforestation, shrinking of ice caps, drying up of inland areas, urban expansion)

gps (galileo satellites can locate a car within the nearest metre)

Front 9

when is damping used

Back 9

to stop components of cars vibrating too long - creates too much noise

reverberation time of a music hall. too long - sound gets fuzzy, too short - hall seems dead

Front 10

effect of damping

Back 10

reduces amplitude

the heavier the damping, the more the time period increases. therefore with heavy damping, there is no oscillation; body moves back to equilibrium position

Front 11

examples of heavy damping

Back 11

sealed test tube floating vertically in water will only oscillate 5 or 6 times before stopping

same test tube in treacle will not oscillate

suspension system of a car. the springing on each wheel of a car gives a smoother ride, but without damping the springs would cause the car to bounce. shock absorbers are used for approximate critical damping so that equilibrium is quickly re-established

Front 12

examples of resonance

Back 12

a rattle in the bodywork of a car when the car is running at a particular speed

a radio or public address system that suddenly makes a very loud squeal

a bridge like the one in Tacoma Narrows which collapsed as a result of winds causing vibrations

Front 13

Barton's Pendulums

Back 13

a large mass oscillating on a string and acting as a driver pendulum for all the small masses attached at intervals to the same supporting string. the small mass on a string of same length as the driver mass has a natural frequency equal to that of the driver pendulum, and it oscillates with a much larger amplitude than any of the other small masses

Front 14

effect of damping on the amplitude of the resonant oscillation

Back 14

increasing the amount of damping reduces the amplitude and slightly reduces the frequency of the driven oscillation

Front 15

practical uses of resonance

Back 15

electrical circuits can resonate; for example tuning radios

mri - magnetic resonance imaging; where nuclei of atoms resonate when in a field of suitable magnetic oscillations

Front 16

annoying effects of resonance

Back 16

buildings vibrate even in steady winds

cars rattle and bounce

wings of planes bounce on take off and landing

Front 17

What is mass?

Back 17

The inertia of an object, or how difficult it is to accelerate the object

Front 18

Give two examples of circular motion

Back 18

A ball on a string

A conical pendulum

Front 19

Give some examples of where conical pendulums are used

Back 19

Theme park rides

Swinging a conker round on a string

Hitting a tennis ball when it is attached to a cord to a vertical pole

Front 20

What equation is used in reference to conical pendulums?

Back 20

tan x = v^2 / Rg

where x is the angle the string makes with the vertical, v is the velocity of the mass, R is the radius, g is the acceleration of free fall

Front 21

Why are oscillations more common than we may realise?

Back 21

Many oscillations that occur happen for only a short time, so they are not thought of as involving oscillation at all

Many oscillations that occur are so fast that our senses do not react to them as oscillations

Many oscillations take place in ways that we simple cannot sense

Front 22

Give 3 examples of oscillations that take a short time

Back 22

Banging on a drum

Hitting a nail with a hammer

Knocking on a door

Front 23

Give two examples of an oscillation that is too fast for us to sense

Back 23

light

warming effect of the sun

Front 24

Give 3 examples of oscillations that we cannot sense ourselves

Back 24

radio waves

X-rays

microwaves from mobile phones

Front 25

What is a free oscillation?

Back 25

an oscillation with no driving mechanism and no friction. therefore there is no effect of damping and the body will oscillate forever

Front 26

Why is momentum a vector quantity?

Back 26

Because it is the product of a scalar and vector