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Uniform Circular Motion - Physics Form 4 Coursework e-Content CDs

Background information

In your form three syllabus, you learnt about linear motion which deals with objects moving in a straight line. In this topic you will learn about objects moving in a uniform circular manner. Examples of such motions are:

The sling

The earth moving around the sun

Racing cars moving in a round racing tracks.

Objectives

By the end of the lesson you should be able to:

-Define angular displacement and angular velocity.

-Describe simple experiments to illustrate centripetal force.

-Explain the applications of uniform circular motion.

-Solve numerical problems involving uniform circular motion.








 






Introduction

In this topic, you will learn about the common terms associated with uniform circular motion, centripetal force and applications of uniform circular motion.


Angular displacement

When an object moves along a circular path from point A to B, the length of the arc AB becomes the angular displacement. Play the animation below to observe this.

The Radian

From the animation above, when the ball covers a displacement AB = r, then the angle subtended at the centre is referred to as one radian.

When the ball covers one circumference (a complete revolution) the displacement equals the circumference of the circle, which is 2Pr.

Therefore 2P radians = 360o

1 radian = 360o/ 2P

= 57.3o

Angular Velocity, W

This is the change of angular displacement with time.

W= do / d t. Click on the play button to make your observations.

Centripetal force

This is the force acting towards the centre of a circle which keeps the object moving in the circle. Click on the play button to make your observations.

Simple experiments to illustrate centripetal force.

Some simple experiments can be used to demonstrate centripetal force. Experiments 1a and 1b are used to demonstrate this.

A photograph of a bucket with some water being whirled in a vertical circle.


Experiment 1a: A rotating mass connected to a spring balance

Click on the play button of the animation below and make your observations.

Observation

As the speed of the rotation increases, the reading on the spring balance increases.

Explanation

The spring balance measures the magnitude of the centripetal force that keeps the mass moving in the horizontal circle.

Experiment 1b: Whirling a bucket with some water.

Play the video below and make your observations.


Explanation

The centripetal force prevents the water from spilling. The force is provided by the hand of the person whirling the bucket.


1. The merry go round.

This is one of the applications of uniform circular motion. Play the video below to see how it works.


Observation

The children are not falling off from the swing. This is because centripetal force prevents them from falling.


Application of uniform circular motion

The following are some of the applications of uniform circular motion:

  • Merry go round
  • Centrifuges
  • Banked roads

The merry go round

This is one of the applications of uniform circular motion. Play the video below to see how it works.


Observation

The children are not falling off from the swing. This is because centripetal force prevents them from falling.

Centrifuge

Below is a video showing a centrifuge in a hospital laboratory. Play the video below and observe how it works.


Cars racing on a banked circular track

Play the video below of formula one cars racing on a banked circular track and observe how they manage to negotiate the bends.



2. Centrifuge

Below is a video showing a centrifuge in a hospital laboratory. Play the video and observe how it works.



3.Cars racing on a banked circular track.

Play the video below of cars racing on a banked circular track and observe how they manage to negotiate the bends.


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