2.3 Bumper Cars

# 2.3 Bumper Cars - Observations About Bumper Cars • Moving...

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1 Key Concepts: 1. Momentum 2. Impulse Observations About Bumper Cars • Moving or spinning cars tend to keep doing so • It takes time to change a car’s motion • Cars often seem to exchange their motions • Heavily loaded cars are hardest to redirect • Heavily loaded cars pack the most wallop Question 1 Does a moving bumper car carry a “force”? – Starting and stopping a bumper car seems to require the “investment” and “withdrawal” of some directed quantity of motion. What is it? Momentum: Mass in Motion • A translating bumper car carries momentum •M om e n t um – A conserved quantity (can’t create or destroy) – A directed (vector) quantity – A measure of difficulty reaching present velocity Momentum = Mass · Velocity Collisions What would happen if the bumper cars had hard steel bumpers rather than rubber bumpers? Exchanging Momentum • Bumper cars exchange momentum via impulses • An impulse is – the only way to transfer momentum – a directed (vector) quantity impulse = force· time • Because of Newton’s third law: When car 1 gives an impulse to car 2 , car 2

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Impulse (motion along a straight line) Impulse = Change in Momentum = Final Momentum – Initial Momentum = mv f –mv i = Δ p Impulse = Force z Time Δ p = m z Δ v = F z Δ t The harder and longer you push a bobsled forward at the start of a race, the more momentum it will have when it starts down the hill. Clicker Question 1 (A) (B) Which person has the greater impulse exerted on his shield? •S e a t b e l t s • Air bags • Padded Dashboards •C r um p l e Z o n e s Why do you care about impulse? Change of Momentum = Impulse p Δ p = F t = F t Final Momentum = 0 p Initial Momentum, p
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2.3 Bumper Cars - Observations About Bumper Cars • Moving...

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