centripetal force and gravity

Question 1

abbreviations

Answer 1

in hback

Question 2

centripetal force

Answer 2

a body is kept moving in a circle by a force called the centripetal force, acting towards the centre of the circle

F = mv²/r (incl notation)

Question 3

the force required depends on:

Answer 3

• the mass of the body
• the speed of the body
• inversely on the radius of the circle

Question 4

uniform circular motion

Answer 4

if a body is in uniform circular motion, its velocity is constant in magnitude but not in direction, so it has acceleration

Question 5

periodic time (T)

Answer 5

the time for one complete revolution

Question 6

Radians

Answer 6

angles can also be measured in radians

If the circumference length is equal to the raidus, the angle is 1 radians

Question 7

angle in radians formula

Answer 7

arc length / radius

Question 8

radians and degrees

Answer 8

180° = π radians

= 3.14159 rad

Question 9

equations

Answer 9

in hback

Question 10

centripetal acceleration

Answer 10

if a body is moving in a circle the acceleration it has towards the centre of the circle is called the centripetal acceleration

Question 11

gravity (Acceleration due to)

Answer 11

• Ignoring air resistance, the acceleration due to gravity is the same for all bodies at the same place
• A body falling freely experiences an acceleration g towards the centre of the earth
• It is always downwards
• 9.8 m/s⁻²

Question 12

Kepler

Answer 12

in 1609 Kepler published his laws of planetary motion which discussed gravity. He published 3 laws

Question 13

Kepler laws

Answer 13

1- The planets move in elliptical orbits round the sun as one focus

2- the line joining the sun and the planets sweeps out equal areas in equal time intervals

3- the square of the periodic time of a planet is proportional to the cube of its distance from the sun

Question 14

Kepler’s Third Law

Answer 14

for the planets + the Moon, the square of the period of the orbit is directly proportional to the cue of the radius of the orbit

Question 15

Kepler equations

Answer 15

hback

Question 16

Derivations

Answer 16

hback

Question 17

circular satellite orbits

Answer 17

hback

Question 18

centripetal force

Answer 18

centripetal force = force of gravity

hback

Question 19

period of an orbit

Answer 19

the time taken for a satellite to go once around the central body is called the periodic time or simply the period (T) of the orbit

Question 20

geostationary/parking orbit

Answer 20

a satellite that has the same period of orbit as the Earth and moves in the same direction is in a geostationary or parking orbit

Question 21

eg of geostationary orbits

Answer 21

communications satellites are geostatic to ensure uninterrupted TV signal

Question 22

Mandatory experiment

Answer 22

• “g” by freefall method

- finding the period of a simple pendulum and hence finding a value for g

Question 23

circular satellite orbits eg

Answer 23

the Moon orbits the Earth and is its only natural satellite

Question 24

particle moving in a circle

Answer 24

tangential speed/linear speed

angular velocity

Question 25

tangential speed/linear soeed

Answer 25

v is called the tangential speed/linear speed of the object | v = velocity / ms⁻¹

Question 26

angular velocity

Answer 26

the rate of change of angle w/ respect to time

Question 27

angular velocity quantity, unit, symbol

Answer 27

scalar quantity unit: rad s⁻¹ (rad per sec) symbol: ω (greek letter omega)

Question 28

constant agnular velocity formula

Answer 28

angle traced out/time

Question 29

If an object is moving in a circular path of radius (r) with constant angular velocity (ω) and constant linear speed (v) then

Answer 29

v = rω

Question 30

proof of v = rω

Answer 30

in hback

Question 31

In what direction does centripetal force apply?

Answer 31

towards the centre

Question 32

Why GPS satellites are not classed as geostationary satellites

Answer 32

- periodic time is not 24 hours | - not in the same place above the Earth

Question 33

1. type of acceleration that the ISS experiences as it travels in a circular orbit around the earth 2. what force provides this acceleration?

Answer 33

1. Centripetal force | 2. Gravitational force

Question 34

Force that makes us go down towards earth (what to label it as on questions)

Answer 34

weight

Question 35

Why do occupants of the ISS experience apparent weightlessness?

Answer 35

they are in freefall / ISS accelerating at same rate as occupants

Question 36

Period of a geostationary communications satellite

Answer 36

1 day / 24 hours

Question 37

forces on a ball on someones hand who's spinning it in a circle

Answer 37

- weight - normal - centripetal

Question 38

It is noted that the freq of the received radio signal changes as a satellite orbits Saturn. Why?

Answer 38

-Doppler effect due to relative motion between source of signal and detector

Question 39

type of force required to keep the ISS in orbit + direction of the force

Answer 39

centripetal force, towards centre of the orbit / towards the Earth

Question 40

An astronaut in the ISS appears weightless. Explain why

Answer 40

they re in a state of freefall, there is no contact force, only force acting is the force of gravity

Question 41

after an orbit, the ISS will be above a diff point on the Earth's surface. Why?

Answer 41

ISS has a diff period to that of the earth's rotation, not in geostationary orbit

Question 42

How many times does an astronaut on the ISS see the sun rise in a 24 hour period?

Answer 42

divide 24 hours by the ISS's period (in hours)

Question 43

how a rotating object can be in equilibrium

Answer 43

constant angular velocity

Question 44

formula for v not in log table

Answer 44

V^2 = GM/R

Question 45

when doing centripetal calculations...

Answer 45

Use radians on calculator!!! The angle in the formulas are in terms of radians, not degree Eg. angular velocity is rad/sec