Chapter 6
Momentum in an isolated system is always conserved.

A collision may result from physical contact between two objects
In any interaction as long there is a force pushing against something then the forces
are equal and opposite.
You cannot have a perfectly elastic collision.na little bit of energy went into the
system. Not all of the energy dissipated. You do not want a car to bounce off of a
bridge when it hits it, because it means the change in acceleration is greater and the
momentum is greater.
You need to know conservation of kinetic energy!!! You need the equation its in the
book.
In elastic collisions both momentum and kinetic energy are conserved.
In an inelastic collision momentum is conserved but kinetic energy is not.
In a perfectly inelastic collision momentum is conserved, kinetic energy is not, and
the two objects stick together after the collision, so the final velocities are the same.
Chapter 7
Rotational Motion
and
The Law of Gravity
The Radian
The radian is a unit of angular measure
The radian can be defined as the arc length s along a circle divided by the radius r
s/r = theta
More About Radians
Comparing degrees and radians
1 radian = 360/2pi
Converting from degrees to radians
Theta(rad)=pi/180 theta(degrees)
Angular Displacement
Axis of rotation is the center of the disk
Need a fixed reference line
During time t, the reference line moves through angle θ
Rigid Body
Every point on the object undergoes circular motion about the point O
All parts of the object of the body rotate through the same angle during the same
time
The object is considered to be a
rigid body
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This means that each part of the body is fixed in position relative to all other parts
of the body
Angular Displacement, cont.
The
angular displacement
is defined as the angle the object rotates through during
some time interval
The unit of angular displacement is the radian
Each point on the object undergoes the same angular displacement
Average Angular Speed
The average angular speed, ω, of a rotating rigid object is the ratio of the angular
displacement to the time interval
Angular Speed, cont.
The
instantaneous
angular speed is defined as the limit of the average speed as the
time interval approaches zero
Units of angular speed are radians/sec
rad/s
Speed will be positive if θ is increasing (counterclockwise)
Speed will be negative if θ is decreasing (clockwise)
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 Winter '08
 Jacobs
 Force, Momentum

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