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Impulse

Impulse. Chapter 8.2. An impulse occurs when momentum is transferred. Impulse Changes Momentum!. The change in momentum depends on the impulse, which is calculated by the impact force times the length of time it acts. Impulse vs. Pressure.

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Impulse

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  1. Impulse Chapter 8.2 An impulse occurs when momentum is transferred

  2. Impulse Changes Momentum! The change in momentum depends on the impulse, which is calculated by the impact force times the length of time it acts.

  3. Impulse vs. Pressure • Pressure is force per unit area of application (same force, less area, more pressure). • Impulse is force applied during a specific amount of time (same impulse, more time, less force)

  4. Impulse The impulse and the change in momentum are the same in each case.

  5. Impulse more time, less force • By increasing the time needed to change the momentum of an object, the amount of force applied per unit time is reduced.

  6. Impulse A rapid transfer of momentum leads to a large impact force • By decreasing the time needed to change the momentum of an object, the amount of force applied per unit time is increased.

  7. 8.2Impulse Changes Momentum If the change in momentum occurs over a long time, the force of impact is . small.

  8. 8.2Impulse Changes Momentum If the change in momentum occurs over a short time, the force of impact is large.

  9. 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. RM

  10. Impulse and Safety • Safety in collisions can be achieved by extending the momentum transfer time in which the impact force acts.

  11. 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

  12. DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Traffic Crash Cushions When you extend the time of transfer, you reduce the force.

  13. DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Air Bags When you extend the time of transfer, you reduce the force.

  14. DEVICES THAT INCREASE MOMENTUM TRANSFER TIME • Bungee Cords When you extend the time of transfer, you reduce the force.

  15. 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.

  16. Impulse • Impulse is the product of force (F) times time (t) • The impulse equation is I = Ft • I is the symbol for impulse • F is the impact force • T is the momentum transfer time • Momentum is transferred through impulse • A change in momentum equals impulse • The time it takes for momentum to be transferred (or change) determines how much force per unit time will be experienced.

  17. 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

  18. 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.

  19. 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.

  20. 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

  21. Combination Momentum and Impulse Question A car with a mass of 1500 kg moves at 10 m/s. What is the momentum of the car? If the car stops in 5 s, what is the braking force needed to stop the car? Step 1—solve for momentum • p = mv [ p = 1500 kg x 10 m/s] • p = 15,000 kg x m/s Step 2—solve for force using the momentum—impulse theorem • mv = Ft or p = Ft • F = change in momentum/time • F = 15,000 kg x m/s 5 s F = 3000 N (braking force required to stop the car)

  22. 8.2Impulse Changes Momentum think! Consider a dish falling and landing on a carpet and on a hard floor. The momentum of the dish is transferred Compare impulse, impact force and time of momentum transfer for each surface. Why does the dish break when it hits the hard floor but does not break when it lands on the carpet?

  23. 8.2Impulse Changes Momentum think! When a dish falls, will the impulse be less if it lands on a carpet than if it lands on a hard floor? Answer: • The impulse would be the same for either surface because the same momentum change occurs for each. • It is the force that is less for the impulse on the carpet because of the greater amount of momentum transfer time. • The impact force is much greater on the dish when it lands on the hard floor because the momentum transfer time has been reduced. This impact force is enough to cause the dish to break.

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