Momentum and collisions AICE Chapter 6 Momentum and collisions

collisions Springy collisions (elastic) One moving ball hits a stationary ball, after the collision the stationary ball is moving while the moving ball is stationary For this to happen the collision must be head on, and the moving ball must not be given any spin All ‘motion’ has been transferred to the other object Velocities have been swapped

collisions Sticky collisions (inelastic) When two objects after a collision move together after impact Football player tackling another player The original ‘motion’ of the one object is shared between the two objects Velocity decreases after impact

What is linear momentum? Momentum is the mass times velocity of an object p= mv The unit of measurement is kg m s-1 , there is no special unit for momentum Momentum is a vector because of the velocity, which means you have to be specific on which direction it is traveling in.

Angular momentum? Momentum of spinning objects

Conservation of momentum Like energy, momentum is also conserved This is when they are in a closed system – no external force acts on them. Within a closed system, the total momentum in any direction is constant For a closed system, in any direction: total momentum of objects before collision = total momentum of objects after collisions

Understanding collisions Crumple zones on cars are intended to absorb kinetic energy for collisions (reduce force by increasing the time to slow down) Rigid cars don’t absorb impact as well and don’t reduce kinetic energy as easily

Perfectly elastic collisions Springy collisions – billiard balls, etc. both momentum and kinetic energy is conserved in this collision pinitial = pfinal Kei = Kef Must keep track of which direction the objects are going before and after the collision Relative speed is based on how fast the two velocities are traveling towards each other

Inelastic collision Momentum is ALWAYS conserved Kinetic Energy is NOT conserved, energy is lost when the two objects collide and move together Energy lost due to heat, sound.

Explosions!!!! Explosions, and recoil typically deal with two (or more objects) at rest in the beginning p= 0 kgms-1 When the object explodes, the total momentum still remains 0 kgms-1 , because all of the momentum of all of the objects are going to cancel each other out due to the direction in which it was traveling in.

Momentum and laws of motion First law basically states that an object that is traveling at a constant speed has momentum, and will only change based on external forces Second law states that a force on an object is directly proportional to the rate of change in momentum. Also the net force and the change in momentum are in the same direction

Falling objects When an object falls to the earth it will undergo an inelastic collision It also follows the 3rd law of motion; for every action, there is an equal and reaction Meaning, that as an object falls toward the earth, the Earth rises up to the object. But since the mass of the Earth is so much greater, the change in velocity is almost imperceptible.

Force in momentum Force can be determined with the following equation F = Δp/Δt F = mv – mu / t F = ma Third law states when two bodies interact, the forces they exert on each other are equal and opposite Magnets will have an equal and opposite force applying on them, and each gain momentum when they pull themselves together.