http://www.youtube.com/watch?v=YFzNKBZehSU Impulse Chapter 8.2 An impulse transfers momentum
Impulse Objectives • What is impulse? • What is the impulse equation? • What occurs through impulse? • How are impulse and change in momentum related? • How does the time of momentum transfer affect the force of impact?
Impulse 1. What is impulse? • Impulse is the product of force (F) times time (t) • an impulse transfers momentum 2. What is the impulse equation? The impulse equation is I = Ft • I is the symbol for impulse • F is the impact force • t is the momentum transfer time • Unit for impulse is N x s (same as kg x m/s) 3. What occurs through impulse? Momentum transfer occurs through impulse
Impulse 4. How are impulse and change in momentum related? Impulse is equal to a change in momentum Ft = ∆mv 5. How does the time of momentum transfer affect the force of impact? The time it takes for momentum to be transferred (or change) determines how much force per unit time will be experienced.
8.2Impulse Changes Momentum impulse = change in momentum Ft = ∆mv • The impulse you give will be the impulse you get back: The force of the impulse will vary inversely with time.
Impulse The impulse and the change in momentum are the same in each case.
Impulse • By increasing the time needed to change the momentum of an object, the amount of force applied per unit time is reduced.
Impulse • By decreasing the time needed to change the momentum of an object, the amount of force applied per unit time is increased.
8.2Impulse Changes Momentum If the change in momentum occurs over a long time, the force of impact is . small.
8.2Impulse Changes Momentum If the change in momentum occurs over a short time, the force of impact is large.
When the bowling ball collides with a barrier, it transfers ___________ to the barrier through _________, which is the product of ________ x __________. Because the bowling ball is moving, it has _______________, which is the product of ______ x __________.
Remember… • Extend the time of momentum transfer, reduce the force of impact. Impulse with large time has small force compared to same impulse with short time, which would have a large force.
Momentum and impulse • Momentum is mass in motion (p = mv) • An impulse transfers momentum (I = Ft). • Impulse remains the same, but time of transfer and impact force will vary inversely. • Impulse = change in momentum Ft = ∆mv Same momentum, same impulse More time, less force Less time, more force
Impulse and Safety • Safety in collisions can be achieved by extending the momentum transfer time in which the impact force acts.
SLOW TRANSFER OF MOMENTUM • Transferring momentum over a longer period of time requires a smaller force. • Consider how materials GIVE The safety net reduces the stopping force on a fallen acrobat by substantially increasing the time interval of the contact
DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Traffic Crash Cushions When you extend the time of transfer, you reduce the force.
DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Air Bags When you extend the time of transfer, you reduce the force.
DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Bungee Cords When you extend the time of transfer, you reduce the force.
QUICK TRANSFER OF MOMENTUM • Transferring momentum in a short period of time greatly increases the impact force! When you reduce the time of transfer, you increase the force.
8.2Impulse Changes Momentum The impulse provided by a boxer’s jaw counteracts the momentum of the punch. a. The boxer moves away from the punch.
8.2Impulse Changes Momentum The impulse provided by a boxer’s jaw counteracts the momentum of the punch. a. The boxer moves away from the punch. b. The boxer moves toward the punch. Ouch!
