Collisions and ImpulseSection 7.3

Collisions and Impulse

• How do measure an impulse?

Collisions

• Large forces occur during collisions

• These forces deform objects

• Deformation occurs because huge jumps in forces happen over a short amount of time

Collisions

• Time of collisions is very short

• We need not worry about the exact time dependence of the force

• We can use average force

Impulse

• Term for the change in forces and the amount of time it takes is impulse

• Impulse =

• Unit = N·s

Impulse

• Can have the same change in momentum

• A large force acting for a short time

• A small force acting for a longer time

• Bend your knees when you land

Why does it matter?

• http://www.youtube.com/watch?v=C08JBiq2eJ4

• If I drop an egg…

Why airbags?

• Driving along, suddenly a brick wall appears in front of you and you crash. Your mass is 60 kg and you were driving 25 m/s. With no airbag, your body comes to rest in 3 x 10-4 s. An airbag can extend the time to rest by a factor of 100. Calculate the two impulses.

Homework

• Read Section 7.3• Do Problems # 15 – 19, Page 188• Bonus # 21• Egg Drop Challenge