2.4+Action+and+Reaction

IV. Action and Reaction A. Newton's Third Law of Motion 1. If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. i. First force = action ii. Second force = reaction 2. Action is all around us 3. 2 different objects - so can't cancel each other out or forces would be added together. 4. Ex - rocket pushed back on the air behind it, air pushes the rocket forward. B. Momentum 1. An object is the product of its mass and its velocity 2. Momentum = mass x velocity 3. Unit for momentum is kilograms -meters per second kg* m/s 4. Described by its direction and velocity 5. More momentum - harder to stop 6. High velocity produces larger momentum C. Conservation of Momentum 1. Law of conservation of momentum i. total momentum of the objects that interact dose not change ii. passes on 1 object to another iii. Quantity of momentum is the same before and after they interact 2. Total momentum of any group objects remains the same unless outside forces action on the objects. i. Friction is an outside force 3. Conservation refers to the conditions before and after some event. i. Quantity is the same at beginning and end ii. 2 moving objects - momentum on 1 decreases while increasing on the other iii. 1 moving object - momentum foes from moving object to stationary object. iv. 2 connected objects - mass is doubled, velocity has to be divided by 2

Quiz 1. Stays the same before and after an event 2. If an object, such as a foot, exerts a force on object, such as a ball, the second object exerts a force of equal strength in the opposite direction on the first object, 3.Momentum = mass x velocity, a slow, moving elephant could have the same momentum as a very fast golf ball 4.160 kg/m/s 5. momentum of car = .04 kg x 4 ms/ = .16 kg/m/s 6. momentum = mass x velocity 7. Total momentum of a group of objects remains the same unless outside forces act on the objects