MOMENTUM? CHAPTER 7 You might have heard people gaining momentum. What is it and how do you get it??? Momentum Store I’d like some please Sure Thing

MOMENTUM? You might have heard people gaining momentum. What is it and how do you get it??? Momentum Store Here you go

Momentum is basically how hard it is to stop something. What would make a moving object hard to stop? MORE MASS (INERTIA) MORE SPEED An object with a lot of mass moving quickly has a lot of momentum

When playing red rover, why do you run instead of walk when trying to break the chain MOMENTUM The faster you are moving the more momentum you have!!!!

Which person would you rather have on your team? The more mass ( for a given speed) the more momentum!! A B

If they are all running the same speed who has the most momentum?

Momentum = mass x velocity p = m v momentum of object Kg m velocity of object (m/s) mass of object (Kg) s Which are vectors both velocity and momentum are vectors

What would happen to the momentum of a cannonball if: speed doubled & mass is constant a.) NO CHANGE b.) x2 c.) 1/2 d.) x4 e.) 1/4

What would happen to the momentum of a cannonball if: speed is constant mass is cut in half a.) NO CHANGE b.) x2 c.) 1/2 d.) x4 e.) 1/4

What would happen to the momentum of a cannonball if: speed is doubled mass is doubled a.) NO CHANGE b.) x2 c.) 1/2 d.) x4 e.) 1/4

Can a bus and a bug have the same momentum?

Momentum = mass x velocity = m v If the boulder and the boy have the same momentum, will the boulder crush the boy? Hint: Which would have the larger speed?

What is the momentum of an 10 kg object moving at 20 m/s? How fast is a 40 kg object moving if it has the same momentum? p = m v

What is the momentum of a 1200 kg elephant at rest?

What does this vector thingee have to do with it? What would direction mean????  = m v THE DIRECTION of momentum is just the Direction of velocity!!!!

If a car (mass constant) had momentum vectors changing as follows what does it mean? What about signs? Positive Negative

If a car (mass constant) had momentum vectors changing as follows what does it mean?

If a car (speed constant) had its momentum vector change as below what does it mean?

What is the velocity of 750 kg rhinoceros, if its momentum is kg m/s?

How do you change the momentum of an object? (like a car at constant mass) p = m v Change the velocity --- Accelerate! How do you accelerate an object? Apply a Force!!

When you step on the gas and apply a force to speed up your car, 2 things determine how much your momentum (speed) changes 1.) 2.) How far you push the pedal - Magnitude of force How long you push the pedal - Duration of force (time)

A force applied for a time is called an: IMPULSE Impulse = F  t Magnitude and direction of force Time force is applied An impulse changes the momentum of an object. More specifically Impulse = Change in Momentum

An object is accelerated from rest by an impulse. How would the change in momentum of the object compare if: The Force was applied for half the time? The Force is twice as strong over the same time IMPULSE = CHANGE IN MOMENTUM

The equation relating Impulse and the change in momentum it causes can be derived very easily: F = m a First a force must be accelerating a mass: What is the definition of acceleration? a = vv tt plugging in for “a”

F = m vv tt Cross multiplying yields form 1 of the equation Applied force time force is applied & time object accelerates F = m vv tt Impulse = change in momentum

F = m vv tt  v = v 2 - v 1 F  t = m(v 2 - v 1 ) F  t = mv 2 - mv 1 F  t = p 2 - p 1 F  t =  p Form 2 of the equation

F  t =  p IMPULSE = change in momentum!!!!

All forces are applied over a time period (An Impulse) Even things that appear to be just for an instant

a balloon decelerating due to an impulse Impact of a racquetball with a wall.

When trying to change the momentum a ball two factors count: 1.) Magnitude of Force - how hard you swing 2.) Duration of Force - Follow through F  t =  p IMPULSE = change in momentum

A speeding car (say 60 mph) can come to a stop two ways Both will have the same  and the same impulse Crashing into a wall Gradually applying brakes  p  F  t BOTH HAVE THE SAME CHANGE IN MOMENTUM

You can stop an object QUICKLY requires a LARGE FORCE FtFt

F tF t BOTH HAVE THE SAME CHANGE IN MOMENTUM Or you can stop an object gradually with a small force

Why is a falling glass more likely to break when it hits concrete than carpet? Objects that cushion, spread the force out over a longer time

What is the safest way to land from jumping off a roof?

What involves the greatest change in momentum Slowing from 60 m/s to rest Quickly or Slowly What involves the greatest IMPULSE? What involves the greatest FORCE?

The puncher wants to deliver a large force over a short time (reducing the momentum of his fist) The puncher could have gently pushed his opponent for a minute and changed his momentum just as much

The puncher wants to deliver a large force, How could the punchee reduce the force? If time of contact with the punch is doubled, what happens to the force of the punch? Rolling with the punches

Other times you want a large force over a short period

Other examples: Air bags Bungee Jumping Crumple Zones in Cars Egg and bed sheet demo

What is the momentum of El Nino (6.0 kg) rolling along at 2 m/s. What is the change in momentum if El Nino comes to a stop? What IMPULSE would be required to do this? What force would be required to stop El Nino in 10 seconds?

A 25 N force accelerates a 1200 kg car from rest to 20 m/s? What is the change in momentum Impulse? How long did it take?

Which has the greater change in momentum A ball that hits and stops? or one that bounces back??

Let’s look at the ball that hits and stops, Lets say it has a mass of 1 kg and is initially traveling at 1 m/s (to the right) After it stops what was the change in momentum?

Now let’s look at the ball that bounces. Again 1 kg and initially moving at 1 m/s (right) and after it bounces it is moving 1 m/s (left)

Which will require a greater impulse ball A ball which hits and stops or A ball that hits and bounces off An object which bounces backwards at the same speed requires twice the IMPULSE. to bring it to a stop accelerate it backwards

Which will hurt more a flower pot which hits your head and breaks, or one which hits your head and bounces off? ouch Force continued

Increasing Impulse Curved blades prolong contact with water: Impulse = F  t Greater impulse means greater change in momentum of the wheel.

A 2 kg ball moving to the right at 4 m/s hits a wall and bounces to the left at 4 m/s. What is the change in momentum. (if needed)

Impulse momentum problems 2, 4, 5, 7, 8, 9, 12, 19, Read Sections 7-1 to 7-4 in book Answer Questions on pages , 15, 21, 24, 27, 35

CONSERVATION OF MOMENTUM. Could you, like, save some momentum for the rest of us.

Which object changes momentum after firing?

What does it mean that momentum is conserved? Which feels the greater force? cannonballsame Which feels the force for the longest time? cannonballsame Think Newton’s 3 rd law!!!

After the cannon fires both the cannon and the ball experience the same IMPULSE (Force x Time) So they both experience the same change in:_________ momentumvelocity speed

After firing? Which has more momentum p = m V Cannonball p = m V THEY BOTH HAVE THE SAME MOMENTUM

They both have the same amount of momentum but something is different…. p = m V Cannonball p = m V THE DIRECTION (consider signs) +5 kgm/s - 5 kg m/s

What do you get if you add up the momentum of the ball and cannon? Cannon ball +5 kgm/s - 5 kg m/s

What was the initial momentum of the ball and cannon? ZERO

The total momentum is the same BEFORE Firing AFTER Firing SUM = ZERO SUM = ZERO

Conservation of momentum: Without an EXTERNAL force the momentum a system doesn’t change. initial momentum = final momentum

A system: Objects of interest We looked at a cannon / ball “system”

No external forces An external force would be from something other than the ball or cannon Here the cannon and ball had no initial momentum, but the outside force gave them both positive momentum

No external forces Would friction be considered an outside force?

Which will change the momentum of a car Pushing a car from the inside Pushing a car from the outside both ONLY pushing the car from the outside changes the momentum because it is an external force

Which will change the momentum of a car Pushing a car from the inside Pushing a car from the outside both Pushing from inside will not change the momentum of the car /person system

Initial momentum = Final Momentum p 1 = p2p2 Does this mean that the momentum of parts of a system don’t change? NO… When you add them up (taking into account + and -) initial momentum = final momentum

Initial Momentum = Final Momentum p jack1 + p jill1 = p jack2 + p jill2 Jack(80 kg) and Jill (40 kg) are at rest initially, After pushing off Jack is moving at +10 m/s, what is Jill’s velocity?

Car & Track Momentum Demos Equal masses stationary Unequal masses stationary

 =mv Say the cannon has a mass of 650 kg and the ball has a mass of 25 kg. After firing the ball flies out at 35 m/s to the right, what is the velocity of the cannon?

What would happen if 2 astronauts played catch? Newton’s cradle applet Astronaut Catch

All of the scenarios we have looked, the objects started from rest. So the momentum always had to add up to ZERO. Like Explosions

Conservation of momentum in collisions In a collision the initial momentum may not be zero. WHY?

2 Main Types of Collisions ELASTIC- objects hit and bounce (no energy is lost) INELASTIC- objects hit and stick together (energy IS lost) BUT MOMENTUM IS ALWAYS CONSERVED

Car & Track Momentum Demos Equal masses 1 moving Elastic Collisions Equal masses both moving opposite directions Equal masses both moving same direction UNEqual masses 1 moving

Car & Track Momentum Demos Equal masses 1 moving INElastic Collisions UNEqual masses lighter moving UNEqual masses heavier moving

Inelastic collision applet

A 4.0 kg car moving 15 m/s hits a 8.0 kg car at rest. What is their velocity after they hit and stick together.

A large 210 kg hobo jumps into to the back of a 670 kg truck moving at 14 m/s. Assuming the hobo has no initial momentum, what is final the speed of the truck and hobo?

WS In Class

A 3 kg car traveling to the right at 5 m/s hit and sticks to a 6 kg car moving to the left at 2 m/s. What is the final velocity of both after the collision?

Deep Space 1 was launched in 1998 and thrusted for 678 days straight. It reached a speed of 4,600 m/s. Drawing of Deep Space 1 Test fire of ion propulsion engine

Rocket Applet Astronaut Catch

Conservation of Momentum Problems (1D) Book Problems page , 28, 32, 35, 37 (2parts)

Conservation of Momentum Lab Recap Applet

Car Crash 2D momentum demo

After the can of gas ruptures how will it move? a.) left b.) right c.) won’t Initial It ruptures

Conservation of Momentum in 2 Dimensions Car A car and a bus collide and stick together. What direction does the wreckage slide?

Car It moves off at an angle But MOMENTUM is Still conserved Car

Conservation of Momentum in 2 Dimensions Draw Vectors for the momentum Car xx YY

Momentum is conserved. So the outcome is just the two momentums added together Car xx YY  total

Car xx YY xx YY  total BeforeAfter  X = 0  Y = 0 The X momentum is conserved The Y momentum is conserved

Car Crash 2D momentum demo

Problems: Honors Physics Page ,39 Physics page 22044, 45, 47 b only

Which has the greater change in momentum a ball that: Hits and sticks or bounces backwards at the same speed? Initial Momentum Final Momentum Change Momentum  = -mv  = 0  = mv  = 0 –(-mv) = mv  = mv –(-mv) = 2mv

ELASTIC COLLIONS (things bounce) & Conservation of momentum

ELASTIC COLLIONS (things bounce) & Conservation of momentum

ELASTIC COLLIONS (things bounce) & Conservation of momentum

ELASTIC COLLIONS (things bounce) & Conservation of momentum