2 Momentum and impulse
In Grade 10 we studied motion but not what caused the motion, in Grade 11 we learnt about forces and how they can alter the motion of an object. In this chapter we will focus on what happens when two bodies undergo a contact interaction and how their motion is affected. We learn more about how force and motion are related. We are introduced to two new concepts, momentum and impulse.
We can begin by considering some scenarios to set the context. Most people have some intuition for physics based on their everyday experiences but they haven’t for- malised it. We can use our intuitive answers to lead into more structured thinking about physical events.
Everyone has experienced a mosquito landing on their arm and it can happen quite unnoticed. Consider the case of a falcon landing on your arm (ignore the sharp claws for now). You would definitely notice, why? What makes a mosquito different to a falcon? Would you still notice if the mosquito flew the same way as a falcon, or if the falcon copied the flight of a mosquito before landing? You probably would still notice, but try to think about what makes them so different.
Look at a motorcycle, motorcar and truck. Which of them is more likely to result in less damage in a collision situation, why? What factors would you change to reduce potential damage.
The factors that come up in these considerations are how fast things are moving and how massive they are. A falcon moving at the same speed as a mosquito still has a much larger mass. Even if a mosquito moved as fast as a falcon it wouldn’t bother us because the mass of a mosquito is so small.
If a motorcycle, motorcar and truck were all moving at the same speed then it would be much safer to be in a collision with the motorcycle but a truck doesn’t have to be moving as fast as a motorcycle to have a huge impact in a collision because of its large mass.
20 2.1. Introduction
Why is the Moon’s orbit largely unaffected when it is hit by asteroid?
There is an interplay between mass and speed (ve- locity to be precise) that governs what would hap- pen if these objects came into contact with an- other object. There are two quantities that depend on mass and velocity, kinetic energy and momen- tum. Kinetic energy is something that we learnt about previous. Momentum is different to kinetic energy and is what we will focus on in the first part of this chapter. In the second part we will cover some of the differences between kinetic en- ergy and momentum.
Key linked concepts
doesn’t require a contact interaction but we won’t consider any non-contact scenarios in this chapter.
• Units and unit conversions — Physical Sciences, Grade 10, Science skills
• Equations — Mathematics, Grade 10, Equations and inequalities
• Techniques of vector addition — Physical Sciences, Grade 10, Vectors and scalars
• Newton’s laws — Physical Sciences, Grade 11, Forces
2.2 Momentum ESCJ7
Chapter 2. Momentum and impulse 21