space physics - circular motion and satellites

Question 1

when is a centripetal force needed

Answer 1

when a circular motion needs to occur

Question 2

in what direction does the centripetal force act

Answer 2

towards the centre of the orbit

Question 3

what are the 4 most likely forces to act as a centripetal force (explained)

Answer 3

gravity - used on an astronomical scale
tension - string or cord connects the object to the centre of the circle
friction - caused by contact with a surface beneath the object
reaction - caused by contact with surface around the edge of the circle

Question 4

describe centripetal acceleration and what causes an acceleration

Answer 4

at any instant, the object is moving at a tangent to the circular path - direction the object would move if the centripetal force is stopped
the unbalanced cp force = acceleration acting towards the centre of the object

Question 5

conclusion of centripetal acceleration

Answer 5

the object is always accelerating; speed is always constant- velocity constantly changes - since direction is always changing

Question 6

equation for centripetal force: F

Answer 6

F = mv^2/r

Question 7

what is newton’s ‘cannon on the mountain’ experiment on keeping in orbit

Answer 7

• ball propelling out of the cannon is too small - ball drops out of orbit
• ball propelling out of the cannon is sufficient but large - the orbital path is longer: orbital time increases
• force is too large - the ball escapes its orbit
• force is just right - the cannonball falls to earth at the same rate as the earth’s surface curves away

Question 8

what is a satellite

Answer 8

an object that has an orbit

Question 9

what are the two types of orbit

Answer 9

geostationary
circumpolar

Question 10

differences between geostationary and circumpolar satellites

Answer 10

geostationary - orbits earth above equator
- orbit every 24h
- orbit with the earth’s rotation so always above the same point
- orbit radius is 6x earth’s radius (6371km)
- only room for 400 gstry satellites

circumpolar - orbits north and south poles
- orbit every 1.5 - 5h
- scans the surface of earth regularly
- orbits a few km above earth
- can have 5 in view at any one time

Question 11

uses of geostationary satellite

Answer 11

• communication: tv, radio, telephone
• gps and satellite navigation
• many other but only limited number of gstry orbits

Question 12

uses of circumpolar satellites

Answer 12

• weather forecasting (detailed)
• land surveys: land usage/mapping etc
• astronomy
• military

Question 13

what are examples of naturally occuring satellites

Answer 13

moon - natural satellite of earth
earth - natural satellite of sun