Topic Three (1.3): Circular Motion Basics

Introduction

Riders on a Ferris wheel move in a circle at mostly a uniform speed. Satellites orbit the Earth with a uniform speed. The concept of speed is fundamentally different than the concept of velocity. This distinction is critical in understanding other concepts related to moving in a circle, such as acceleration and a resultant force that causes it. In this topic you will learn about angular displacement in radians and in degrees and convert between these units. You will define angular velocity, centripetal acceleration along with deriving an equation for it, and make calculations using both. You will explain that a centripetal force is required to produce and maintain circular motion and an equation for this force will be used.

Reading

Edexcel International AS/A Level Physics Student Book 2 pages 14 to 18

Tasks

Complete the following:

  • Read pages 16 to 18 of the textbook, read the worked examples on pages 17 and 18.

WATCH – Trigonometry – Angle Measures – Degrees and Radians (YouTube) Links to an external site.

WATCH – Angular and Linear Velocity Definitions (YouTube) Links to an external site.

WATCH – Circular Motion – A Level Physics (YouTube) Links to an external site.

WATCH – Equations of Circular Motion (YouTube) Links to an external site.

SIMULATION – Uniform Circular Motion (Physics Classroom) Links to an external site. Complete the activity using the interactive link.

COMPLETE – Gameboard: Units of Rotary Motion (Isaac Physics) Links to an external site.

  • Complete the worked examples again (cover the solutions, check your answers at end).
  • Complete the questions on page 18. You will find the answers in General Resources under the heading Textbook Answers. Download Textbook Answers.

Extend

  • Stretch and Challenge – Calculate the acceleration of an object which rests on the Earth’s equator and compare this to the acceleration the object would experience if it were in the UK. How do these two accelerations differ, and does this affect the weight of the object?
  • Wider reading – When a car is travelling fast enough, it can be made to perform a vertical loop on a track. Investigate the factors that need to be considered when trying this stunt. How is the radius of the loop linked to the mass of the car and the speed it needs to travel to complete the loop safely?

Top Tips

Make sure that you understand the following key points:

  • There is no special centrifugal force. Any resultant force that makes an object move in a circle is labelled as the centripetal force. Any object travelling in a circle must be directed towards the centre of the circle. What would happen if the force acting on the object were pushing outwards?
  • Radians is a unit for angle. Make sure you change your calculators to radians if considering angles.
  • Make sure that you know the differences between angular velocity and speed in circular motion, including the correct units for each.

Key Terms

Add the following key terms with definitions to your word list:

  • Radian
  • Angular displacement
  • Angular velocity, ω
  • Centripetal acceleration
  • Centripetal force