6.1 - Circular Motion

Question 1

Is velocity a scalar or vector?

Answer 1

Vector.

Question 2

Is acceleration a scalar or vector?

Answer 2

Vector.

Question 3

What is uniform circular motion?

Answer 3

Motion in a circle at a constant speed.

Question 4

What is happening to the speed, direction and velocity of an object in uniform circular motion?

Answer 4

An object in uniform circular motion has a constant linear speed
It is also constantly changing direction, meaning there is a constantly changing velocity.

Question 5

What does it mean if an object has a constant speed but a changing direction?

Answer 5

It means there’s a constantly changing velocity, meaning the object must be accelerating.

Question 6

What is centripetal acceleration?

Answer 6

The acceleration of an object towards the centre of a circle when an object is in motion (rotating) around a circle at a constant speed.
This is perpendicular to the direction of the linear speed.

Question 7

In what direction does centripetal force and acceleration act?

Answer 7

Towards the centre of the circular path.

Question 8

What is angular displacement defined as?

Answer 8

The change in angle, in radians, of a body as it rotates around a circle.

Question 9

What is a radian defined as?

Answer 9

The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.

Question 10

What is the equation for angular displacement?

Answer 10

Δθ = Δs/r
Δs = length of the arc, or the distance travelled around the circle (m)
r = radius of the circle (m)

Question 11

What is the conversion from degrees to radians?

Answer 11

θ° x π/180 = θ rad

Question 12

What is the conversion from radians to degrees?

Answer 12

θ rad x 180/π = θ°

Question 13

What is angular speed defined as? (⍵)

Answer 13

The rate of change in angular displacement with respect to time.

Question 14

What is the equation to calculate angular speed?

Answer 14

⍵ = Δθ/Δt
Δθ = change in angular displacement (radians)
Δt = time intervals (s)

Question 15

How else can angular speed be calculated? (using time period and frequency equation)

Answer 15

⍵ = v/r = 2πf = 2π/T
v = linear speed
r = radius of orbit
T = the time period
f = frequency

Question 16

What are some equations for centripetal acceleration?

Answer 16

a = v²/r
v = linear speed
r = radius of the circular orbit
a = r⍵²
⍵ = angular speed
a = v⍵

Question 17

What is centripetal force defined as? (F)

Answer 17

The resultant force towards the centre of the circle required to keep a body in uniform circular motion. It is always directed towards the centre of the body’s rotation.

Question 18

How can you calculate centripetal force?

Answer 18

F = mv²/r = mr⍵² = mv⍵
m = mass
v = linear velocity
⍵ = angular speed
r = radius of the orbit

Question 19

What is the unit for angular speed?

Answer 19

rad s⁻¹

Question 20

What other force (other than centripetal) would be acting if a car is travelling around a roundabout?

Answer 20

Friction between car tyres and the road.

Question 21

What other force (other than centripetal) would be acting if a ball is attached to a rope moving in a circle?

Answer 21

Tension in the rope.

Question 22

What other force (other than centripetal) would be acting when Earth is orbiting the Sun?

Answer 22

Gravitational force.