1. You’re Quite Impulsive
An Introduction to Impulse and Momentum

2. A Review of What We Know About Motion
Chapters 2 & 3 introduced us to vectors such as displacement, velocity, and acceleraton
No mass was included
Chapter 4 introduced forces and mass into the mix
Chapter 5 has brought the concept of energy to motion. It includes mass and motion but not as vectors
Chapter 6 will combine the vectors of motion with mass quantities

3. Where (and why) We Start
Vector Motion
Energy Analysis
A ball is thrown up at 25m/s at 53o above horizontal. Find final velocity.
How we solve:
Strengths:
Weaknesses:
A ball is thrown up at 25m/s at 53o above horizontal. Find final velocity.
How we solve:
Strengths:
Weaknesses:

4. How we can combine both strengths
We need a quantity that expresses motion with a mass component and a directional component.
Welcome to the world of impulse and momentum!
Impulse: force times time- force is a vector; time is not. It expresses an effort and duration. Units are Ns or kgm/s
Momentum: mass times velocity- mass is scalar; velocity is vector. It includes direction and size. Units are kgm/s or Ns.

5. How Momentum and Impulse relate
As an object moves with a velocity it has a “quantity” of motion that relates to its size and motion. This is momentum (m x v)
Newton’s 2nd law tells us that an outside force will create a proportional velocity change.
The longer the force acts the more the change in velocity.
So, the force acting for a time creates a m-v (momentum) change.
How Momentum and Impulse relate
Momentum= mass x velocity
Velocity changes are expressed as accelerations: acc = Dv/Dt
Accelerations are created by forces acting on masses
The “longer” the force acts the more the object accelerates
Force = mass x (Dv / Dt)
After a little algebra
Force x Dt = mass x Dv
Impulses create momentum changes

6. A Few Examples
If a 25.0 kg cart rolls at 15 m/s east and a 200. N force (west) acts on it for 30.0 seconds,
(a) what is its initial momentum and kinetic energy?
(b) what is its final momentum, velocity and kinetic energy?
A 50.0 kg object travels at 30.0 m/s east. A N (south) force acts on the object for 15.0 seconds.
(a) What is its final momentum?
What is its final velocity?
What is its final kinetic energy?