Circular motion DONE

Question 1

Describe the difference between an object’s speed and its velocity in circular motion.

Answer 1

The object travels at constant speed
Velocity is changing because it is a vector
Magnitude of velocity remains the same but the direction varies continuously

Question 2

Explain why an object in circular motion accelerates in terms of velocity.

Answer 2

An object in circular motion is constantly changing direction so its velocity is constantly changing
Acceleration=change in velocity/ time so the object must be accelerating

Question 3

Describe what centripetal acceleration is and what causes it.

Answer 3

Centripetal acceleration is constant acceleration towards the centre of a circle
The acceleration is caused by a resultant force( centripetal force)
Which acts at right angles to the direction of movement of the object

Question 4

Explain centripetal force, centripetal acceleration and linear velocity in terms of 2 of Newton’s laws.

Answer 4

N2L tells us that if an object is accelerating it must be experiencing a resultant force (F=ma)
So an object in circular motion must experience a centripetal, resultant force to cause its centripetal acceleration
N1L tells us an object will remain at rest or continue to travel at constant velocity unless a resultant force acts on it
So without the force, the object that was in circular motion would move inertially in a straight line. This velocity is the linear velocity

Question 5

Define angular displacement and write down its units.

Answer 5

The angle through which a point has been rotated in a given direction

Radians

Question 6

Define angular speed/ velocity and what is its unit.

Answer 6

How many radians a point turns through per second
+ direction for velocity
Rad s^-1

Question 7

Define linear speed/ velocity and what is its unit.

Answer 7

The instantaneous speed/ velocity of an object at any point in its circular path
Linear speed is always constant
m s^-1

Question 8

Define frequency and what is its unit.

Answer 8

How many circles/ revolutions a point makes per second

Hz or s^-1

Question 9

Define time period and what is its unit.

Answer 9

How much time it takes a point to make 1 turn/ revolution

s

Question 10

How is the centripetal, resultant force affected by mass and linear velocity of an object?

Answer 10

Centripetal, resultant force increases as mass or magnitude of velocity increases

Question 11

How is the centripetal, resultant force affected by the circle’s radius?

Answer 11

It decreases as radius increases

Question 12

Explain why work done against resultant, centripetal force is zero for an object moving in circular motion and state how and why this affects the object’s speed.

Answer 12

Work done= Force x Distance moved in direction of force

Distance moved in direction of force is zero because the object never gets any close to the centre of the circle which is where the force is directed

So work done is 0

No work done means no energy transferred so object’s speed is constant

Question 13

State where the resultant force is always directed.

Answer 13

The centre of the circle

Question 14

Where on the circular path does an object have the biggest resultant force?

Answer 14

At the top

Question 15

Name 3 providers of centripetal force.

Answer 15

Gravity
Tension
Friction

Question 16

On a conical pendulum, what are the vertical and horizontal components of tension equal to and how does this affect vertical and horizontal acceleration?

Answer 16

The vertical component of the tension equals the weight of the mass
So there is no acceleration vertically
The horizontal component of the tension provides a resultant force towards the centre of the circle
So there is centripetal acceleration

Question 17

What is apparent weight?

Answer 17

What you feel through your feet, equal to reaction force

Question 18

What is weightlessness and what is the value of centripetal acceleration when you feel weightless?

Answer 18

When reaction force is 0
So you are in free fall
Centripetal acceleration= g/ 9.81

Question 19

Why do you feel an outwards( centrifugal) force when you experience circular motion?

Answer 19

Because your momentum is straining against the centripetal force

Question 20

State the direction in which friction acts and explain why this is in terms of tendency to move.

Answer 20

Inwards
Because friction opposes a tendency to move
So because objects in circular motion have a tendency to move in a straight line tangential to circular motion
The friction opposes this tendency to move “outwards” so acts inwards

Question 21

What increases the chance of a car skidding/ slipping and why?

Answer 21

Anything which reduces friction
Worn tyres, ice, oil
Because the centripetal force is friction
so if this is reduced then a higher centripetal acceleration is required to maintain circular motion