Circular Motion

Question 1

Why is an object, that is moving at a constant speed, in a circle accelerating?

Answer 1

• its direction of motion is constantly changing
• therefore, its velocity is constantly changing
• as acceleration is the rate of change of velocity, it is accelerating

Question 2

a, F and v on object moving in circle

Answer 2

a is always to the centre of the circle
F is always towards the centre of the circle
v is in a straight line pointing to direction of movement

Question 3

Angular displacement

Answer 3

between two points the object will have moved through angle θ
may be measured in degrees or radians (360 degrees = 2pi radians)

Question 4

Angular velocity

Answer 4

is the angular displacement divided by time taken

Question 5

Period

Answer 5

is the time taken for the object to travel once around the circle

Question 6

Frequency

Answer 6

is the number of times the object travels around the circle per second

Question 7

Banked Corners

Answer 7

when a car travels around a bend on a flat road, sideways friction between the tyres and the road produce the centripetal force
on a banked corner, the car can travel much faster because the centripetal force comes from the horizontal component of the normal reaction force
Normal reaction force resolved:
- vertical forces are balanced FRcosθ = mg
- horizontal forces are unbalanced FRsinθ provides centripetal force

Question 8

Vertical Circular Motion vs Horizontal Circular Motion

Answer 8

• the size of the normal reaction force acting on the object varies throughout the motion
• the speed of the object may not be constant as energy changes between Ek and Ep

Question 9

Newton’s Universal Law of Gravitation

Answer 9

every single point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation

Question 10

Gravitational Field

Answer 10

a region of space where a mass experiences a force because of its mass

Question 11

Gravitational Field Strength

Answer 11

the force per unit mass experienced by a small point test mass placed in the field

Question 12

Types of Orbits around Earth

Answer 12

Equatorial orbit - needed for geostationary orbits, goes over the equator (looking over same places every time)
Polar Orbit - going over poles, (observing the whole earth)

Question 13

Why do astronauts feel weightless?

Answer 13

weight depends on the reaction force
the ISS and the astronaut are falling together so reaction force = 0