What is Momentum Momentum may be defined by

What is Momentum? Momentum may be defined by its equation: Momentum is a quantity defined as the product of the mass and velocity of an object.

Unit of Momentum • The equation illustrates that momentum is directly proportional to an object’s mass and the object’s velocity.

Momentum’s Proportionality

Momentum is a vector quantity • Back to the Bowling Ball: To fully describe the momentum of a 5 kg bowling ball, moving westward at 2 m/s, you must include both the magnitude and the direction of the bowling ball’s momentum. (It would not be enough to just say the ball has 10 kg. m/s momentum. )

Momentum: Sample Problem

Changing Momentum • A change in momentum takes force and time. To stop an object, it is necessary to apply a force against its motion for a given period of time.

Changing Momentum In football, the defensive player applies a force for a given amount of time to stop the momentum of the offensive player with the ball.

Changing Momentum Serway/Faughn - Physics

Changing Momentum • A force is applied to an object to change its momentum. • Impulse – the product of the force, and the time over which the force is applied. Serway/Faughn - Physics • Impulse – Momentum Theorem – the impulse experienced by the object equals the change in momentum

Changing Momentum

Sample Problem: Force needed for change in momentum (impulse)

Sample Problem: Force acting on a car while braking.

Sample Problem: Force acting on a car while braking. (The car on the last slide. )

Changing Momentum Increasing the time of an impact can reduce the force of a collision. This Inupiat (Alaska native people) Family is playing a traditional game. The blanket stretches and extends the time of collision so that the change in the girl’s momentum occurs over a longer time interval. A longer time interval requires a smaller force to change the girls momentum, than if she fell directly to the ground (not a good idea. ) Serway/Faughn - Physics

Skydiver Lisa Boyer fell 3, 810 meters after her parachute failed to open. She landed in a sludge pond and survived ---unhurt! If Boyer had landed on solid ground, she would have come to a crashing halt in about 0. 0001 sec. The concentrated force of that abrupt landing would have killed her instantly.

• But she landed in the sludge pond of a sewage treatment plant. The soft, squishy sludge brought her body to rest in about 0. 03 sec ---30 times longer than if she landed on sold ground. Falling into sewage sure is gross, but it beats the alternative. • Because the force of the impact was distributed over this longer time, it was never strong enough to cause serious injury. (Science World)

Window washer Chris Saggers fell 22 stories to the roof a car. He walked away with only a broken elbow. If he had hit the roof feet first, the force would have been focused in a small area, shattered his legs, and driven the bones into his spine. But Saggers landed sprawled out, with the force of impact distributed evenly over his body. (Science World) The car roof crumpled so it lengthen the time of the impact.

Conservation of Momentum The total momentum of all objects interacting with one another remains constant regardless of the nature of the forces between the objects.

Soccer Ball Collision & Conservation of Momentum

Soccer Ball Collision & Conservation of Momentum Elastic Collision

Conservation of Momentum & Collisions • In every interaction between two isolated objects, the change in momentum of the first object is equal and opposite to the change in momentum of the second object.

Conservation of Momentum & Collisions

Conservation of Momentum & Collisions – Boater Problem

Types of Collisions • Perfectly inelastic collisions – When two objects collide and move together as one mass ---they stick together after the collision. (like a meteorite and the earth)

Types of Collisions • Perfectly inelastic collisions

Types of Collisions Elastic collision: two objects collide and return to their original shapes with no change in kinetic energy. Here again, the total momentum remains constant.

Types of Collisions