Topic Two (1.2): More Collisions

Introduction

Momentum, a vector quantity, is conserved in interactions such as collisions and explosions. Often, to understand such processes, it is necessary to resolve the momentum of objects in two (or more) dimensions. These experiments show students how non-linear interactions can be analysed.

A resultant force on an object causes it to accelerate causing a change in the velocity of the object for as long as it acts. A resultant force applied over a longer time therefore produces a bigger change in momentum than the same force applied over a shorter time. The change in momentum is therefore equal to the product of the average force and the duration of the collision when in contact. Conversely, a small force applied for a long time produces the same change in momentum - the same impulse - as a larger force applied briefly.

Reading

Edexcel International AS/A Level Physics Student Book 2 pages 6 to 13

Edexcel International A Level Physics Lab Book pages 40 to 43

Tasks

Complete the following:

  • Read pages 6 to 9 of the textbook, studying the worked example on page 6.
  • Pay particular attention to the Practical Skills boxes on pages 6, 7 and 8.

WATCH – Verifying the Principle of Conservation of Momentum with an Air Track (YouTube) Links to an external site.

SIMULATION – Elastic and Inelastic Collision (Walter Fendt) Links to an external site.

COMPLETE – Tutorials on Momentum, Impulse and Collision (Khan Academy) Links to an external site.

WATCH – Momentum and Impulse with Solved Problems (YouTube) Links to an external site.

WATCH – Impulse and Momentum in Sport (YouTube) Links to an external site.

WATCH – Practical – Newton's Second Law (YouTube) Links to an external site.

WATCH – Conservation of Momentum in 2 Dimensions (YouTube) Links to an external site.

WATCH – Conservation of Linear Momentum - Bozeman Science (YouTube) Links to an external site.

SIMULATION – Collision Lab (PHET). Links to an external site. Explore 2D collisions and consider inelastic and elastic conditions.

COMPLETE – Gameboard: Force and Momentum (Isaac Physics) Links to an external site. and Impulse (Isaac Physics) Links to an external site.

Extend

WATCH – Wringing Out Water on the ISS (YouTube: Canada Space Agency) Links to an external site.  This shows the behaviour of water droplets in free fall on the International Space Station.

  • Stretch and challenge – Describe how their collisions could be analysed in three dimensions.
  • Wider reading – Research some of the more complex aspects of collisions, such as the rotation of objects and angular momentum. This can be applied to scenarios such as snooker, football, and even collisions in the Solar System.

Practical Knowledge

  • Use ICT to analyse collisions between small spheres e.g. ball bearings on a table top. (Core Practical 10)

WATCH – A-Level Core Practical 10 (Vimeo: Abingdon Physics Videos) Links to an external site.

REVIEW – Tracker (Physlets) Links to an external site. Use this free software to analyse your results for Core Practical 10.

  • Work through pages 40 to 43 in the Lab Book.

Top Tips

Make sure that you understand the following key points:

  • Make sure you understand the vector nature of momentum and how the conservation laws apply in situations where the collisions are not limited to a straight line.
  • In ‘show that’ questions, you must state the equations you use. Then substitute in values and calculate a final answer that rounds to the approximate value in the question. Give the answer to 1 significant figure more than given in the question to prove you have calculated it yourself, and that it matches with the number in the question.

Key Terms

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

  • Impulse

Consolidate

Now consolidate your understanding by working through these additional resources:

  • Read the ‘Thinking Bigger’ section on page 10.
  • Complete the questions in the two boxes on page 11.

REVIEW – Revision Notes - Physics Factsheet: ‘Combined Notes - Unit 4 Edexcel Physics A-Level’, ‘4.3. Further Mechanics’ (Physics and Maths Tutor) Links to an external site.