CHAPTER 8 MOMENTUM
to extend time and decrease force what do you do when jumping from an elevated position how much is force decreased to
bend knees so it can go back to original shape decreases force by 10 to 20 times
IMPULSE (WHAT FACTORS DOES IT DEPEND ON) (FORMULA)
change in momentum the force and the length of time that it acts on and object Impulse= Ft
what are the two most powerful tools of mechanics?
conservation of momentum conservation of energy
elastic collisions
end result= objects colliding are separate without being permanently deformed and without generating heat' net momentum (before collision) = net momentum (after collision) (momentum 1)+(momentum 2)= (momentum 1)+(momentum 2)
to extend time and decrease force what do you do when catching the ball
extend hand and catch it then cradle it
if you want to decrease impact in impulse what do you do?
extend the time
to change the momentum of something what type of impulse should it be
external because for example if you want the basketball to move it wont move by itself without an external force, since the forces come in balanced pairs that cancel in project
WHAT ARE FACTORS THAT AFFECT MOMENTUM
mass speed can have a large momentum if it has a large mass or speed or both
WHAT IS MOMENTUM
mass in motion mass x velocity
in real life are perfect collisions common + explanation + examples are perfectly elastic collisions common?
no it will be before and just right after collision however external forces will ruin that perfect collision some time after collision billiard balls after colliding experience friction with table and air that slows down momentum in space an example of perfect collisions being ruined is by gravity no
increasing impulse
optimally you want to increase both time and force or either of those factors
decreasing momentum why would you choose having a car hit the stack of hay instead of a concrete wall.
the car is stopped by the same impulse, but remember the same impulse means the same product of force and time, not the quantities of it. sooo, you would hit the hay of stack because time would be greater thus decreasing the amount of impact or force.
if time is extended 100 times the force of impact is reduced by how much?
100 times
CHANGE IN MOMENTUM (FACTORS THAT COULD MAKE IT CHANGE) (WHAT IS THE MOST COMMON CASE FOR CHANGE IN MOMENTUM) (RELATIONSHIP BETWEEN FORCE AND CHANGE IN MOMENTUM)
Velocity or mass Usually velocity Since, momentum usually changes due to velocity, it accelerates. Force produces an acceleration, so the greater the force the more it accelerates, thus the greater change in momentum.
examples of the law of conservation of momentum
atomic nuclei undergoing radioactive decay cars colliding stars exploding
why is the cannon cannon ball system net force zero before and after launching zero?
the force causing it to recoil is equal and opposite to the recoil newton's third law for every reaction there must be and opposite and equal force also the forces applied to the system are internal
IMPULSE MOMENTUM RELATIONSHIP
the greater the impulse exerted on an object, the greater change in momentum impulse=change in momentum
if there are no external forces then..
there is no impulse, thus no change in momentum
what does conserved mean
when any quantity in physics does not change
inelastic collisions
when collisions are permanently deformed and produce heat end result= objects are stuck together net momentum (before collision) = net momentum (after collision) (momentum 1)+(momentum 2)= (total mass)(velocity)
what is true about the vector sum of momenta in a collision
when objects are in momentum and split in half, the two halves have the same momentum before it split
when are collisions an example of the law of conservation of momentum
when objects collide in absence of external forces, then the net momentum of both objects before the collision equal net momentum of both objects after collision net momentum (before collision) = net momentum (after collision)
law of conservation of momentum
when there are no external forces, the momentum of a system remains unchanged.
are impulses greater when an object bounces why
yes because there are two impulses one to bring it to stop and another to go back up
at the microscopic level are perfectly elastic collisions common
yes electrically charged particles bounce off one another without producing heat