0:12 [Music]
0:14 collisions happen when two or more
0:16 objects come into contact with each
0:19 other and a transfer of momentum and
0:22 kinetic energy occurs
0:25 collisions occur every time you hit a baseball
0:26 baseball
0:28 bounce a basketball
0:31 or play pool
0:33 when objects collide in the absence of
0:36 external forces they form a system in
0:38 which the net momentum of both objects
0:41 before the collision equals the net
0:43 momentum of both objects after the collision
0:45 collision
0:48 there are two types of collisions
0:50 elastic collisions
0:53 and inelastic collisions
0:56 an elastic collision is defined as one
0:59 in which no kinetic energy is lost no
1:01 damage is done to the objects involved
1:05 and there is no generation of heat
1:07 in the real world no collision is
1:10 perfectly elastic because so many other
1:13 forces come into play like friction
1:16 air resistance
1:22 however the game of pool offers a fairly
1:25 good elastic representation
1:27 pool tables and billiard balls are
1:29 designed to reduce the effects of friction
1:30 friction
1:33 resulting in close to ideal elastic collisions
1:35 collisions
1:37 when the cue ball hits the resting eight
1:40 ball it sets the eight ball in motion
1:43 having transferred all of its momentum
1:45 and kinetic energy the cue ball comes to
1:47 a rest
1:49 the net momentum of the cue ball before
1:52 the collision equals the net momentum of
1:55 the eight ball after the collision
1:57 momentum and kinetic energy are
2:00 transferred and conserved
2:02 if the eight ball is already in motion
2:04 when a similarly moving cue ball
2:06 collides with it then the eight ball
2:09 will gain some of the initial cue ball's
2:13 momentum and the net momentum before and
2:17 after the collision will be conserved
2:19 if the eight ball and the cue ball are
2:21 traveling at the same speed and collide head-on
2:22 head-on
2:24 then they will bounce off of each other
2:26 with the same momentum but in opposite
2:29 directions their momentum and kinetic
2:37 the second type of collision is an
2:40 inelastic collision in an inelastic
2:42 collision momentum is still conserved
2:45 but kinetic energy is lost in the system
2:48 resulting in the creation of heat
2:52 and damage done to the colliding bodies
2:55 bodies that are involved in an inelastic
2:57 collision end up entangled with each
3:03 a clear example of an inelastic
3:06 collision is a car crash in order to
3:08 understand the conservation of momentum
3:11 in this example we'll imagine a car
3:13 crash taking place in a world where road
3:15 friction and air resistance have no
3:17 bearing on the system
3:21 let's take two cars a and b with equal mass
3:22 mass
3:26 car b is parked when car a plows into it
3:28 head on at a velocity of 10 meters per second
3:30 second
3:32 kinetic energy is immediately lost as
3:34 the cars become mangled and stuck
3:37 together some energy is converted into heat
3:38 heat
3:41 momentum after the accident however is
3:44 conserved with no road resistance the
3:46 doubly massive car wreck will continue
3:49 moving in the same initial direction as
3:57 the after collision momentum is easily
4:00 calculated using the conservation of
4:03 momentum equation
4:06 where the mass of car a times its speed
4:07 of 10 meters per second before the collision
4:09 collision
4:12 is equal to the mass of car a plus the
4:15 mass of car b times the final velocity
4:24 rearranging the equation to solve for
4:28 the velocity after the collision
