Chapter 7 Impulse

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Chapter 7Impulse Momentum
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7.1 The Impulse-Momentum Theorem
Why is a glass less likely to break when dropped
on carpet than on a tile floor?
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Forces may not be constant during an impact.
In these cases, we will use the average force
that occurred during contact time.
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?t contact time (s)

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A larger impulse produces a larger change in
velocity (?v).

butthe ?v depends on the mass also.
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Momentum (p)
inertia in motion
mass (kg)
velocity (m/s)
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Impulse-momentum theorem
Impulse change in momentum
A larger impulse produces a larger change in
velocity.
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Why does following-through on a swing increase
the drive distance of a ball?

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Youre travelling down the road and you car
suddenly goes out of control but you have a
choice of slamming into a haystack or a brick
wall. Which would you choose?

Why?
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Decreasing Momentum

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When you jump off a step, you usually bend your
knees as you reach the ground. By doing this,
the time of the impact is about 10 times more
what it would be in a stiff-legged landing and
the average force on your body is reduced by
_______.

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Why is a glass less likely to break when dropped
on carpet than on a tile floor?
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ASSIGNMENTRead 7.1Ch. 7 Problems 1,2,8 Page
206
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7.2 The Principle of Conservation of Linear
Momentum
The total momentum of an isolated system remains
constant (is conserved).
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System collection of objects being considered.
Internal Forces forces objects exert on each
other within the system.
External Forces forces exerted on the objects
from outside the system.
Isolated System The net external forces are
zero.
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ASSIGNMENT Read 7.2Ch. 7 Problems
17,18,19page 207
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7.3 Collisions in One Dimension
Elastic Collision total KE does not change
before/after collision.
bouncy
Inelastic Collision total KE is not the same
before and after collision.
sticky
Completely Inelastic Collision objects stick
together.
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Things to Know Impulse Momentum Impulse
change in momentum Momentum is conserved unless
there is a net external force. Elastic and
Inelastic Collisions
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Try TheseCh. 7 Problems 28, 31 p. 208 28.
2.13 m/s 31. a) v5kg -0.4 m/s, v7.5kg 1.6
m/s b) 0.8 m/s
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Coefficient of Restitution (C.O.R.)
bounce height
drop height
For objects bouncing off floor.
C.O.R represents the collision not the object.
C.O.R 1, perfectly elastic, C.O.R. 0,
inelastic
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Rain vs. Hail
Impulse change in momentum
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