Lets start with everyday language What do you say when a sports team is on a roll? They may not have the lead but they may have ___________ MOMENTUM A team that has momentum is hard to stop.
What is momentum? Momentum: p=mass x velocity What does this mean in the physical world? Which is harder to stop a soccer ball or a bowling ball moving at the same speed? Explain why? What about a bullet? Explain why?
What is Conservation? Conserved describes a quantity that may change during some process, but does NOT appear from nowhere or disappear without a trace. In an isolated system, certain physical quantities are conserved, such as mass and energy. Lets see how it works!
Is Momentum Conserved?Conserved When there is a collision between two objects, Newton's Third Law states that the force on one of the bodies is equal and opposite to the force on the other body. Newton's Third Law Therefore, if no other forces act on the bodies (in the direction of collision), then the total momentum of the two bodies will be unchanged. Hence the total momentum before collision in a particular direction = total momentum after in a particular direction.
What is Impulse? As the force acts upon the object for a given amount of time, the object's velocity is changed. Remember Newtons 2nd law equation: F = ma & a = v/ t F = m v/ t F t = m v F t = m(v f – v i ) Impulse (J) = change in momentum
To change the momentum of a body, a force must be applied to the mass. The longer this force is applied to the mass, the greater effect it will have on changing the momentum. IMPULSE – A force applied for a period of time which results in a change of momentum
Why does an egg break or not break? An egg dropped on a tile floor breaks, but an egg dropped on a pillow does not. Why? FΔt= mΔv In both cases, m and Δv are the same. If Δt goes up, what happens to F, the force? Right! Force goes down. When dropped on a pillow, the egg starts to slow down as soon as it touches it. A pillow increases the time the egg takes to stops.
Car Crash Would you rather be in a head on collision with an identical car, traveling at the same speed as you, or a brick wall? Assume in both situations you come to a complete stop. Take a guess! http://techdigestuk.typepad.com/photos/uncategorized/car_crash.JPG
Car Crash (cont.) The answer is… It Does Not Matter! Look at FΔt= mΔv In both situations, Δt, m, and Δv are the same! The time it takes you to stop depends on your car, m is the mass of your car, and Δv depends on how fast you were initially traveling.