Download momentum

Impulse Newton’s second law of motion,
F = ma, can be rewritten by using the
definition of acceleration as the change in
velocity divided by the time needed to make
that change. It can be represented by the
following equation
Multiplying both sides of the equation by
the time interval, Δt, results in the
following equation:
The right side of the equation, mΔv, involves
the change in velocity: Δv = vf – vi.
Therefore, mΔv = mvf – mvi. The product of
the object’s mass, m, and the object’s velocity,
v, is defined as the momentum of the object.
Momentum is measured in kg•m/s. An object’s
momentum, also known as linear momentum, is
represented by the following equation.
Momentum is a VECTOR quantity – that means we
must describe it with a number telling us how BIG it
is (we call that “magnitude”), AND a number telling
us the direction the object which has this
momentum is moving.
This will then give us the “Impulse
Momentum Theory”
or…
FΔt = Δp
Momentum in a Closed, Isolated System
Under what conditions is the momentum of the
system of two balls conserved? The first and
most obvious condition is that no balls are lost
and no balls are gained. Such a system, which
does not gain or lose mass, is said to be a closed
system.
The second condition required to conserve the
momentum of a system is that the forces involved
are internal forces; that is, there are no forces
acting on the system caused by objects outside of
it.
Let’s do a problem on the board…
A 35.0-g bullet moving at 475 m/s strikes a
2.5-kg bag of flour that is on ice, at rest. The
bullet passes through the bag, as shown in
Figure 9-7, and exits it at 275 m/s. How fast
is the bag moving when the bullet exits?
Nearly 400 years ago, Johannes Kepler observed that comet
tails appeared to be blown by a solar breeze. He suggested
that ships would be able to travel in space with sails designed
to catch this breeze. Thus, the idea for solar sails was born.
How Does a Solar Sail Work?
A solar sail is a spacecraft without an engine. A solar sail
works like a giant fabric mirror that is free to move. Solar
sails usually are made of 5-micron-thick aluminized polyester
film or polyimide film with a 100-nm-thick aluminum layer
deposited on one side to form the reflective surface.
(By the way... a micron, short for
micrometer, is a unit of
measurement equal to one millionth
of a meter. A micron is actually
0.000039 of an inch.)
Reflected sunlight, rather than rocket fuel, provides the force.
Sunlight is made up of individual particles called photons. Photons
have momentum, and when a photon bounces off a solar sail, it transfers its momentum to the sail, which propels the spacecraft along.
The force of impacting photons is small in comparison to the force
rocket fuel can supply. So, small sails experience only a small amount
of force from sunlight, while larger sails experience a greater force.
Thus, solar sails may be a kilometer or so across.
Photons supplied by the Sun are constant. They
impact the sail every second of every hour of
every day during a space flight. The Sun’s
continuous supply of photons over time allows the
sail to build up huge velocities and enables the
spacecraft to travel great distances within a
convenient time frame. Rockets require enormous
amounts of fuel to move large masses,