Impulse & Momentum 1

Think About It! Is a pin more likely to move rapidly when a bowling ball travels toward it at a high speed or at a low speed?

What if you had two bowling balls of different masses move at the same speed, which is more likely to move the pin? Let’s Ask Bill Nye!

Why do falling hailstones have the capacity to damage cars and buildings?

Momentum Is it harder to stop the Titanic or a rubber ducky if they are traveling at the same speed? We say that Titanic has more MOMENTUM than the rubber ducky. Momentum is inertia in motion.

Momentum: the product of an object’s mass and velocity. p = mv Vector

How is momentum calculated? Formula p = m x v Units kg m/s = kg x m/s Abbreviations p = momentum m = mass (kg) v = velocity (m/s) 7

Impulse

Impulse The result of force acting on an object for a specific time. Impulse (J): J = FΔt Units: Newton Seconds (N s) Vector

Impulse-Momentum Theorem Impulse is the area under a Force vs. Time Graph

Impulse-Momentum The greater the force, the greater the acceleration. Therefore, there is a greater change in velocity, and a greater change in momentum.

F = ma = m v t = m v p F t m v = p Impulse = change in momentum (Newton’s Second Law) = m v t = m v p F t m v = p Impulse = change in momentum

30,000 N of force acting for 1.0 s (a crash!) A 1000 kg car moving at 30 m/s (p = 30,000 kg*m/s) can be stopped by 30,000 N of force acting for 1.0 s (a crash!) or by 3000 N of force acting for 10.0 s (normal stop)

Impulse-Momentum Theorem Impulse = change in momentum can be written as: J = Δp OR F Δ t = mΔv Impulse is Ft. We just saw on the first slide. Momentum is mv. The triangle just means the change.

MOMENTUM Ft Decreasing Momentum: Which would it be more safe to hit in a car ? Ft mv mv Ft

MOMENTUM In each case, the momentum is decreased by the same amount or impulse (force x time) Hitting the haystack extends the impact time (the time in which the momentum is brought to zero). The longer impact time reduces the force of impact and decreases the deceleration. Whenever it is desired to decrease the force of impact, extend the time of impact !

Why have most cars had metal bumpers replaced with plastic ones? 18

Other improvements made by the department of transportation 19

Impulse-Momentum Theorem-Football Football Collisions

Why is a catcher’s mitt different? 21

“Roll with the punches” 23

Parkour! (How to survive a landing) Advanced Rolling Decrease the change in momentum Increasing the time of contact decreases the force. 24