Circular Motion

What is circular motion?

Motion of an object which follows a circular path around a centre point.

What is linear speed (v) in circular motion?

The speed at which the object moves along its circular path, measure in m s^-1.

What is angular speed?

The rate of change of angular position.(Angular speed is measured in rad s-1.)

What is the formula that links linear speed (v), angular speed (ω \ omega ), and radius (r)?

V = ω r

v = linear speed (ms-1)

ω \ omega = angular speed (rad s-1)

r = radius (m)  

What is the formula that links angular speed (ω \ omega ) and time period (T)?

ω = 2 π / T

ω \ omega = angular speed (rad s-1)

T = time period (s)

How many radians are there in one full revolution?

2π

How can you convert from radians into degrees?

To convert from radians into degrees:

Angle in degrees = angle in radians x (180 / π)

What is centripetal force?

The force acting towards the centre of motion which keeps the object travelling along a circular path.

What is centripetal acceleration?

The acceleration experienced by an object moving in a circle.

What is the formula linking centripetal acceleration (a), linear speed (v), and radius (r)?

a = v^2 / r

a = centripetal acceleration (m s-2)

v = linear speed (m s-1)

r = radius (m)

Which direction does centripetal force act in?

Towards the centre of the circular path.

What is the angle between the centripetal force and velocity of an object travelling along a circular path?

90°

What is the formula linking centripetal force (F), mass (m), linear speed (v), and radius (r)?

F = m (v^2) / r

F = centripetal force (N)

m = mass(kg)

v = linear speed (m s^-1)

r = radius (m)

A car is travelling over a humpback bridge.

What is the normal reaction force when the car loses contact with the bridge?

Zero

A ball attached to a string is swung in a circle in the vertical plane.

When will the tension in the string be greatest?

When the ball is at the bottom the tension will be greatest.

A ball attached to a string is swung in a circle in the vertical plane.

When will the tension in the string be lowest?

When the ball is at the top the tension will be lowest.

A ball attached to a string is swung in a vertical circle. 

When the ball is at the bottom of the circle, what is the relationship between the centripetal force (F), weight of the ball (W), and tension (T) in the string?

T = F + W

T = tension (N)

F = centripetal force (N)

W = weight of ball (N)

A ball attached to a string is swung in a vertical circle. 

When the ball is at the top of the circle, what is the relationship between the centripetal force (F), weight of the ball (W), and tension (T) in the string?

T = F - W

T = tension (N)

F = centripetal force (N)

W = weight of ball (N)

A race car travels around a circular track. 

Where does the centripetal force come from?

The friction between the tyres and the road.