Download Work and Power 13.1

Work and Power
13.1
Work – force is applied to an object and the
object moves in the direction as the applied
force
Work = Force x distance
W=Fxd
**Work is zero when an object is not moving
Measuring Work
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Joules – SI Units
1 J= 1 N x m = 1kg x m2 / s2
Power
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Power – the rate at which work is done, or
how much work is done in a given amount
of time
Power = work/time
P = W/t
Watts – SI units
1 W = 1 J of work in 1 second.
Machines & Mechanical Advantage
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How do Machines make work easier?
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Change size of an input force
change the direction of the force
decrease distance over which force is applied
this is – multiplying the force
mech. Adv. = output force/input force
= input distance/output dist.
Mechanical Advantage
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output force/input force, or input
distance/output dist
No units – expressed as a number
** a machine that has a mechanical
advantage greater than one multiplies the
input force.
** a machine with mechanical advantage
less than one increases distance and
speed. Can this occur?
Momentum
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Momentum = mass x velocity
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P = m v, v = P/m, m=P/v
P – momentum
 M – mass
 V – velocity (speed + direction)
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SI units – kg m/s
Momentum has direction...indicated by
velocity
Momentum
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Momentum increases as mass and velocity
increase
If an object’s velocity is zero, it’s
momentum is zero
Decreasing an objects Momentum will
decrease it’s Force
Conservation of Momentum
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The total amount of momentum in an
isolated system is conserved.
Momentum is transferred from one object
to another in a given collision.
Total momentum before objects collide
equals the total momentum after the
collision.
Impulse
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The effect of a net force acting on an
object (a kind of "moving force")
The product of the average net force
acting on an object and its duration.
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J = F Δt
Impulse–momentum theorem - the
change in momentum of an object equals
the impulse applied to it
Impulse
Impulse