NOTE TO INSTRUCTORS:
OBJECTIVE:
THEORY:
FUNDAMENTAL CONCEPTS:
Linear momentum is conserved if
the net force acting on an object is zero. This follows from
the equation which relates the change in momentum to the impulse given
to the object.
Clearly if the force is zero, the impulse is zero and the
change in momentum is zero, hence the momentum remains constant.
A simple such system may consist of two particles, let us call them A and B,
interacting with each other. The force on particle A
is equal and opposite to the force
acting on particle B:
. Because the times during which the forces
act are the same,
it follows that the changes in momentum of the
two particles are also equal and
opposite, so that the total change in momentum is zero.
The conservation of momentum is therefore a consequence of Newton's III
Law.
In collisions, provided there is no net external force on any of the bodies, the sum of the initial momenta
equals the sum of the final momenta:
For one dimensional processes the physical quantity that is conserved is linear momentum.
A collision is called totally inelastic if the two bodies stick together
after colliding. The conservation of momentum for a one
dimensional totally
inelastic collision is then:
A collision of two bodies is called totally elastic if
energy is conserved in the process. In this case the result of the
collision in one dimension can be calculated by
APPARATUS:
You should be able to complete this brief quiz before proceeding.
SUGGESTIONS:
PROCEDURE I - INELASTIC COLLISION - EQUAL MASSES
PROCEDURE II - ELASTIC COLLISION - EQUAL MASSES
In this experiment you will be measuring the velocities of two
bodies with equal masses, before and after a totally elastic collision.
PROCEDURE III - ELASTIC COLLISION - UNEQUAL MASSES
Calculate
and record the percent difference
.
Calculate
and record the percent difference
.
JAVA APPLET:
Interesting resources on the web
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Elastic collisions Conservation of energy and momentum This applet animates elastic collisions of two point masses. The user enters the ratio of the target mass to the projectile mass and the ratio of the projectile's final speed to its initial speed, and the applet animates the collision in the target rest frame and in the center of mass frame. |