5.2 Circular motion

Question 1

Define the word radian.

Answer 1

Radian- The angle subtended at the centre of a circle when the arc of a circle when the arc is equal length to he radius of the circle.

Question 2

Define the word period?

Answer 2

Period/ time period is the time taken for one complete circular path.

Question 3

Define angular velocity.

Answer 3

Angular velocity- the rate of angular rotation.

Question 4

What is angular velocity measured in?

Answer 4

Radians per second, rad s^-1

Question 5

What is centripetal acceleration?

Answer 5

The acceleration of an object moving with uniform circular motion. The centripetal acceleration is directed radially inwards towards the centre of the circle, perpendicular to the velocity vector at any instant.

Question 6

What is the symbol for angular velocity?

Answer 6

Lowercase omega, ω

Question 7

What are the equations for centripetal acceleration?

Answer 7

• a = v²/r
• a = ω²r

Question 8

What is 60° equal to in radians?

Answer 8

π/3 radians

Question 9

How can you measure any angle in radians?

Answer 9

Measure the length of the arc, c, divide the length of the arc by the radius, r, of the circle.

θ= c/r

Question 10

What is 360° equal to in radians?

Answer 10

2π radians

Question 11

What is 180° equal to in radians?

Answer 11

π radians

Question 12

What is 90° equal to in radians?

Answer 12

π/2 radians

Question 13

How is the time period and frequency of a circular rotation related?

Answer 13

f = 1/T

Question 14

What is the difference between speed and velocity?

Answer 14

speed is a scalar quantity, so only considers magnitude, while velocity is a vector quantity so we have to consider its magnitude and direction.

Question 15

How can you describe the velocity in relation to circular motion? What does this cause?

Answer 15

The velocity of an object moving in circular motion is constantly changing, although its speed is constant, it’s direction is constantly changing. This means the object would always be accelerating.

Question 16

In what direction in centripetal acceleration?

Answer 16

The acceleration must be in the direction towards the centre of the circular path, along the radius of the circle.

Question 17

Define centripetal acceleration?

Answer 17

The acceleration of a body moving in a circle with a constant speed.

Question 18

Why is an object always accelerating when moving in a circular motion?

Answer 18

As acceleration is defined as the rate of the change of velocity, the object can be described as accelerating because due to it’s change of direction.

Question 19

What is centripetal force?

Answer 19

Centripetal force is the resultant force on an object, acting towards the centre of the circle, causing it to move in a circular path.

Question 20

What are the equations for centripetal force?

Answer 20

• F= mv²/r
• F= mω²r

Question 21

What force is responsible for centripetal acceleration?

Answer 21

Centripetal force.

Question 22

What examples of forces can be types of centripetal forces?

Answer 22

• Frictional force
• Gravitational force
• Electromagnetic force
• Force of tension

Question 23

How can a frictional force be an example of a centripetal force?

Answer 23

For example, the friction between the tyres on a turned wheel and the road acts inwards and provides the centripetal force to keep the car moving in a circle.

Question 24

How can a gravitational force be an example of a centripetal force?

Answer 24

For example, gravitational attraction between the satellite and the earth provides the centripetal force. The combination of this force and the orbital speed of the satellite keeps it moving in a circle.

Question 25

How can a electromagnetic force be an example of a centripetal force?

Answer 25

For example, the electrostatic attraction between the electrons and protons provides the centripetal force.

Question 26

How can a force of tension be an example of a centripetal force?

Answer 26

For example, the force of tension in a string provides the centripetal force , keeping the bung rotating in a circular path.

Question 27

What experiment can we do to investigate centripetal force?

Answer 27

Using a whirling bung.

Question 28

What is the method to investigate centripetal force with a whirling bung?

Answer 28

1. Thread a rubber bung and make a mark on the string 0.3m away from the bung.
2. Attach a 1N weight at the other end of the string and whirl the rubber bung in a horizontal circle.
3. Adjust the speed of rotation so that the radius of the circle is constant and equal to 0.3m, then continue to whirl the bung at a constant speed.
4. Measure the time for 10 revolutions of the bung.
5. Determine the speed of the bung using v=s/t. Since the bung is making 10 revolutions, then v= 10x 2πr/t which simplifies to v= 20πr/t.
6. Repeat for different values of centripetal force by adding different forces to the bottom.
7. Pot of graph of F against V².
8. Gradient will equal m/r.
9. Determine the mass of the bung and and the value of r from the gradient.

Question 29

When doing the whirling bung experiment, what safety precautions should be taken?

Answer 29

Wear eye protection and work outside if class room is too full.

Question 30

When an object is travelling in a vertical circle, where till the string experience the most tension and why?

Answer 30

At the bottom of the circle as the object’s weight would be acting in the opposite direction to the centripetal force.

Question 31

When an object is travelling in a vertical circle, where till the string experience the least tension and why?

Answer 31

At the top of the string because there is already a downwards force acting on the string of the objects weight acting in the same direction as the centripetal force.