QW What is the unit for momentum? How do you tell if something is harder to stop? If velocity is increased, and momentum remains the same, what happens to mass? What is the difference between inertia and momentum? What does magnitude mean? What is the difference between vector and scalar?

Impulse

Impulse Unikitty and Batman are coming toward you, who is harder to stop? m= 3 kg v= 1 m/s m= 90 kg v= 1 m/s

Impulse But, how do you stop Batman? You apply a force.

Impulse In order to stop Batman (or anything else) you must apply a force. When you stop something, you are changing it’s momentum. You apply a force.

Impulse A change in momentum created by a force exerted over time is called impulse. Basically, impulse is a change in momentum.

Impulse If the momentum of an object changes, either the mass, the velocity, or both change

Impulse Which do you think is more likely to change: the mass of an object, or the velocity of an object?

Impulse If the mass remains unchanged, which is most often the case, then the velocity changes and WHAT occurs?

Impulse Acceleration Remember: acceleration is a change in velocity

What produces acceleration? Impulse What produces acceleration?

Impulse Force

Impulse The greater the force acting on an object, the greater its change in velocity, and therefore, the greater its change in momentum

Impulse How long the force acts is also important. If you apply a brief force to a stalled car you changed the car’s momentum.

Impulse If you applied the same force over an extended period of time you will produce a greater change in the car’s momentum.

Impulse A force sustained for a longer time produces more change in momentum than does the same force applied briefly.

Impulse BOTH Force and Time are important in changing momentum.

Impulse - examples Boxers attempt to move with an opponent’s punch when it is thrown. In other words, a boxer moves in the same direction as their opponent's punch. This movement may prevent a knockout blow being delivered by their opponent. Explain how.

Impulse - examples If the force applied by the opponent's punch can be extended over a longer time, the force of the blow is reduced, minimizing the chances of a knockout punch being delivered to the boxer.

Impulse - examples An egg dropped on a tile floor breaks, but an egg dropped on a pillow from the same height does not. Why?

Impulse - examples In both cases, the mass and velocity are the same. In this type of example, if the amount of time the object is in contact with the force goes up, then the amount force goes down. When dropped on a pillow, the egg starts to slow down as soon as it touches the pillow. The pillow increases the amount of time it takes the egg to stop.

Can you throw an egg, and not break it? https://www.youtube.com/watch?v=7RSUjxiZnME

Impulse In physics, the quantity Force • time is known as impulse.

Impulse = change in momentum This is how it looks on your STAAR chart: Units?

Both sides are Impulse: Impulse = Ft Impulse = m(vf-vi) J = Ft J = m(vf-vi) So you will be expected to solve using either side, but sometimes you will have to use the entire formula.

Impulse – practice problem A net force of 25 newtons is applied to a 20 kilogram cart for 2 seconds? What is the impulse? What is the change in momentum?

Impulse – practice problem A net force of 25 newtons is applied to a 20 kilogram cart for 2 seconds? What is the impulse? F= 25 N Impulse=Ft m= 20 kg (25)(2)=50 N*s t= 2 s What is the change in momentum? 50 kg*m/s

Impulse – guided practice A net force of 30 newtons is applied to a 10 kilogram cart that is already moving at 1 meter per second. The final speed of the cart was 2 meters per second. For how long was the force applied?

Impulse – guided practice A net force of 30 newtons is applied to a 10 kilogram cart that is already moving at 1 meter per second. The final speed of the cart was 2 meters per second. For how long was the force applied? Ft = m(vf-vi) (30)(t)=(10)(2-1) 30t=10 t=.3 s F= 30 N m= 10 kg vi= 1 m/s vf= 2 m/s

Impulse – practice problem A 0.045 kg ball is thrown (from rest) with a force of 450 N. If the force acts on the ball for 12 s, what is the final speed of the ball?

Impulse – practice problem A 0.045 kg ball is thrown (from rest) with a force of 450 N. If the force acts on the ball for 12 s, what is the final speed of the ball? F= 450 N m= .045 kg vi= 0 m/s t= 12 s Ft = m(vf-vi) (450)(12)=(.045)(vf-0) 5400=(.045) vf 120,000 m/s =vf

Impulse – practice problem A .5 kg frisbee is thrown from rest to a final speed of 12 m/s. What is the impulse of the frisbee?

Impulse – practice problem A .5 kg frisbee is thrown from rest to a final speed of 12 m/s. What is the impulse of the frisbee? m= .5 kg vi= 0 m/s vf= 12 m/s J = m(vf-vi) J =(.5)(12-0) J = 6 kg*m/s

Impulse-Practice Problem A tennis player hits a ball during a tennis match. Compared to the magnitude of the impulse given to the ball, the magnitude of the impulse given to the bat is? A) Same B) More C) Less

Impulse-Practice Problem A tennis player hits a ball during a tennis match. Compared to the magnitude of the impulse given to the ball, the magnitude of the impulse given to the bat is? A) Same