Momentum Happy New Year!

Bathroom Policy Please record our new bathroom policy in your notebook: First complete the sign out clipboard in the back of the room like you have in the past. Next fill out the new hall pass. Make sure you have my signature before you leave the room* *This requires you to have my full attention, which means you may need to wait for me to finish my current task before you can use the restroom so plan ahead and use the restroom during passing period!

Talk with your neighbor Where have you heard the word momentum used? What was it used to describe

Quick Facts  Momentum-"mass in motion" all objects have mass, if an object is moving then it has momentum. Momentum=p Momentum is dependent on mass and velocity.  P=m*v What would be momentum's units? Is momentum a vector quantity? Why/why not?  Kg*m/s

p=m*v Momentum Equation What is the momentum of a 1 kg cart traveling 2 m/s? What happens if the cart mass is doubled?  What happens if the cart velocity is tripled?  How are mass and momentum related? How are velocity and momentum related? P=2 kgm/s P=4 kgm/s P= 6kgm/s

Plicker Practice Problems A car possesses 20,000 units of momentum. What would the car's new momentum be if: Velocity was tripled?  Mass doubled?  Mass & velocity both double?  Answer Options for 1-3: A. 20,000 B. 40,000 C. 60,000 D. 80,000 Determine the momentum of: 4. 60kg halfback moving eastward at 9 m/s  A. 7 kg*m/s B. 54 kg*m/s C. 540 kgm*/s D. 0 kg*m/s 5. 1000kg car moving northward at 20 m/s  A. 2000 kg*m/s B. 20,000 kg*m/s C. 200,000 kg*m/s D. 0 kg*m/s   6. 40kg freshman moving southward at 2 m/s A. 20 kg*m/s B. 40 kg*m/s C. 60 kg*m/s D. 80 kg*m/s

Since p=m*v, if the velocity of an object is changing... Remember... Unbalanced forces acting upon an object causes acceleration. When a forces acts opposite the object's motion it slows down When a force acts in the same direction of an object's motion it speeds up Since p=m*v, if the velocity of an object is changing...  MOMENTUM IS CHANGED!!!

Impulse Impulse is the change in momentum F=m*a --> F=m*(Δv/t) --> F*t=m*Δv Where F*t is impulse & m*Δv is the change in momentum Impulse: F*t=I F: Force t: time Change in momentum m: mass Δv: change in velocity

Impulse and Collisions In a collision an object experiences a force acting for a certain amount of time that results in it mass undergoing a change in velocity.  ^Impulse-momentum change theorem: F*t=m*Δv Impulse-Momentum Change Principles: Impulse experienced by an object=force*time Momentum change of an object is the mass* velocity change Impulse=momentum change

Plicker Practice Problems Which scenario has the greatest Δv? Acceleration? Momentum change? Impulse?

Plicker Practice Problems Which scenario has the greatest Δv? Acceleration? Momentum change? Impulse?

Plicker Practice Problems Which scenario has the greatest Δv? Acceleration? Momentum change? Impulse?

The Effect of Collision time on Force Impulse 100 1 50 2 25 4 10 0.1 1000 How are force and time related in the theorem F*t=m*Δv As the time over which a collision occurs increases the force acting upon the object decreases.  What is the purpose of following through in baseball? What is the purpose of riding the punch?  What scenarios can you think of when collision time should be increased? Decreased? 

The rebound Effect When some objects collide they bounce off each other, resulting in a change in direction, large velocity & momentum change. To reduce the rebound effect in car collisions, crumple zones have been used in car designs. Why is it more beneficial for a car to crumple in a collision than rebound?  Reduces  force and impulse

1/3 Opener Fill in the blanks F*t=Impulse=M*∆v=momentum change Force (N) Time (s) Impulse (N*s) Mom. Change (kg*m/s) Mass (kg) Vel. Change (m/s) 0.010 10 -4 0.100 -40 -200 50 -20000 -8 1.0

1/5 Opener

Momentum & Conservation  

Newton’s 3rd Law In every interaction, there is a pair of forces acting on the two interacting objects. The size of the force on the first object equals the size of force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs, equal and opposite action- reaction force pairs. F1 = -F2 With your partner discuss your understanding of Newton’s 3rd Law. Come up with a scenario that describes this law. Paraphrase Newton’s 3rd Law in your own words. In a collision between two objects, both objects experience forces that are equal in magnitude and opposite in direction. https://www.youtube.com/watch?v=gXqNzLW9lHU

Momentum Conservation Principle Momentum lost by object 1 is equal to the momentum gained by object 2. In a system momentum is a constant unchanging value. System: collection of two or more objects An isolated system is free of external forces. In this system the only forces that contribute to the momentum change of an individual object are the forces acting between the objects themselves.

Kinetic Energy: The energy of motion Collisions Elastic Collisions Both momentum & kinetic energy are conserved Inelastic Collisions  Only momentum is conserved  Preview for next unit:  Kinetic Energy: The energy of motion KE=1/2m*v2 Scalar quantity

How do I find the Momentum of two colliding objects?! Ex. A 10 kg cart (A) travels at a velocity of 5 m/s collides with a 10 kg cart (B) at rest. What is the momentum of the system? What is the final velocity of the carts? I like to make a table to identify momentum before and after: Then final velocity can be calculated: 10kg*v+10kg*v=50kg*m/s--> 20kg*v=50 -->v=2.5m/s P Before Collision  P After Collision Momentum Change Cart A Cart B Total  P Before: 50, 0, total:50 P After: 25, 25, total:50 Mom Change –25, 25, 0

Practice Problem  In a physics experiment, two equal-mass carts roll towards each other on a level, low-friction track. One cart rolls rightward at 2 m/s and the other cart rolls leftward at 1 m/s. After the carts collide, they couple (attach together) and roll together with a speed of _____________. Ignore resistive forces. P Before Collision  P After Collision Momentum Change Cart A 2 Cart B -1 Total  1 P Before: 2, -1, Tot:1 P After: ½, ½, Tot:1 Mom Change: -1.5, 1.5, 0