Would you rather be hit by a tennis ball or a bowling ball?

To answer the question, you would want to consider mass but also velocity. That is momentum.

momentum = mass x velocity Momentum is inertia in motion. Ex: What is the momentum of a 10 kg bowling ball moving at 20 m/s ? p = m x v p = 10 kg x 20 m/s p = 200 kg m/s

What would you have to change to change momentum? To change momentum, you can change mass or velocity. What is the name for a change in velocity? Acceleration.

What does it take to cause an acceleration? A force is needed to cause an acceleration. The longer a force is applied, the greater the change in momentum.

Baseball Golf Soccer Many sports involve a change in momentum.

Impulse is a physics term that relates a force and the amount of time it is applied. force x time = impulse Example: What impulse is applied to a baseball if the batter uses a 50 N force for 0.2 seconds?

F = 50 N t = 0.2 s Impulse = force x time 50 N x 0.2 s = 10 Ns

It is impulse that causes a change in momentum. So Ft = ∆ p Ft = p f - p i Ft = mv f - mv i

What is the change in momentum if a 1000 kg car accelerates from 20 m/s to 50 m/s? 30,000 kg m/s

A 5 kg mouse is moving at 10 m/s. If he comes to a stop, what was his change in momentum? m = 5 kg v i = 10 m/s v f = 0 m/s final momentum = 0 kg m/s initial momentum = 50 kg m/s ∆ p = 0 kg m/s – 50 kg m/s ∆ p = - 50 kg m/s The negative indicates a loss of momentum.

Example: A 20 kg object starts at rest. In 5 s, it has a speed of 100 m/s. How much force was used? 400 N

Give examples of a moving object coming to a rest. How could you minimize the force felt by these objects? Give examples of ways in which the time for an object to stop is increased. Airbags

A 800 kg car is moving at 30 m/s. The driver slams on the breaks. It takes the car 3 s to stop. What force did the brakes supply? N The negative indicates the force is in the opposite direction of the motion. If the driver of the car above eased on the breaks for 30 s to come to a stop, how much force did the breaks supply? N

Example: A 40 N force is applied to a 5 kg object for 10 s. If the object was initially moving at 20 m/s, what is its new speed? 100 m/s

Conservation of Momentum Physics Definition: In the absence of an external force, the momentum of a system remains unchanged. A system can be one or more objects. Example of internal forces: explosions collisions

The recoil of a gun is a good example of conservation of momentum. Gun Recoil Another Example On A Larger Scale

Inelastic Collisions In an inelastic collision, the objects involved in the collision stick together after they collide. An Example

Conservation Of Momentum For Collisions The momentum before a collision is equal to the momentum after a collision. momentum before = momentum after

A 5 kg object moving at 10 m/s collides with a 10 kg object at rest. After the collision, the 5 kg object stops moving. What is the speed of the 10 kg object?

Inelastic Example A 1000 kg car moving at 20 m/s strikes another 1000 kg car at rest. Afterwards, they stick together. What is their speed? V = 10 m/s

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A 0.50 kg object is at rest. A 3.00 N force to the right acts on the object during a time interval of 1.50 s. What is the new speed of the object? 9 m/s

A 2500 kg car travelling to the north is slowed down uniformly from an initial velocity of 20.0 m/s by a 6250 N braking force acting opposite the car’s motion. What is the car’s velocity after 2.50 s? 13.8 m/s

A 6.00 g bullet moving at 375 m/s is fired into a stationary 5.50 kg wooden block which is at rest on a flat surface. After moving 7.00 cm, the block and the embedded bullet come to a rest. What is the coefficient of friction? 0.12

Ballistic Pendulum

A 7.50 g bullet moving at 420 m/s is fired into an 8.00 kg ballistic pendulum. How high does the pendulum rise? cm

An elastic collision is one where both the momentum and the kinetic energies are conserved. A 4.0 kg bowling ball sliding to the right at 8.0 m/s has an elastic head-on collision with another 4.0 kg bowling ball initially at rest. The first ball stops after the collision. Verify that kinetic energy is conserved.

Calculate the recoil velocity of a 4.0 kg rifle that shoots a kg bullet at a speed of 280 m/s m/s

A ball of mass kg moving with a speed of 4.50 m/s collides head on with a kg ball at rest. If the collision is perfectly elastic, what will be the speed and direction of each ball after the collision? 1.50 m/s and 6.00 m/s

A 1500 kg car traveling east with a speed of 25.0 m/s collides inelastically at an intersection with a 2500 kg van traveling north at speed of 20.0 m/s. Find their velocity after the crash N of E