Linear Momentum and Collisions Overview

Introduction

In the last module, we considered energy relationships which is the approach that Gottfried Leibniz, one of Isaac Newton's rivals, favored. Newton on the other hand favored the concept of momentum to explain the physical world. In fact, in Newton's Principia, he never stated that F=ma. Rather Newton viewed forces as being equal to the rate of change of momentum. As we will see, this turns out to be the equivalent of F=ma. So who was right, Newton of Leibniz? They were both right, but each of their views of physics were best adapted to particular types of problems. The task at hand is to model and predict not the motion of just one object, but rather what happens when two or more objects collide. The concept of momentum is best suited to this task.

Essential Questions

What is linear momentum?
Under what circumstances is moment conserved in a collision?
When two or more objects collide and bounce off each other, is kinetic energy conserved?
When two or more objects collide and bounce off each other, is the collision elastic or inelastic?
When two or more objects collide and stick together, is kinetic energy conserved?
When two or more objects collide and stick together, is the collision elastic or inelastic?
Is an exploding object an elastic collision, inelastic collision, or not a collision at all?
What is impulse?
How is impulse related to linear momentum?
Why is the impulse momentum theorem important to safety concerns, such as seat belts, air bags and cushions for stunt men?
Is momentum conserved independently in orthogonal directions?

Key Terms

elastic collision - A collision in which kinetic energy is conserved.'
impulse - The product of average force and the length of time the force is applied.
impulse momentum theorem - A statement that the product of average force and time of application is equal to the change in linear momentum.
inelastic collision - A collision in which kinetic energy is not conserved.
linear momentum - A vector quantity that is the product of mass and velocity.

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