Section 2: Conservation of Section 2: Conservation of Momentum and ExplosionsMomentum and Explosions

Quick Q’sQuick Q’sQ: U R stuck in space and R given a carbon fiber nano tube rope that is connected to the earth so that U may pull your self back. 1) when pulling on the rope, which pulls harder you or the earth?2) Will the earth budge, why of why not?3) Who has the greatest change in momentum?

Law of conservation of Law of conservation of MomentumMomentumDemos:Demos:1) Colliding marbles 1) Colliding marbles 2) Basket ball and little ball2) Basket ball and little ball3) Student body check3) Student body checkTotal Initial Momentum = Total Final Momentum

Under what conditions will this not be true?

For Momentum to be For Momentum to be ConservedConserved1) Must be a closed system: Where

the mass of the system does not change.

2) All forces on the system must be internal: where there are no external forces from outside contact or field forces.

-this is considered to be an isolated system

Demo: Student on cartDemo: Student on cart1) What will happen to the cart if the student starts 1) What will happen to the cart if the student starts moving forward?moving forward?2) What will happen to system (student and cart) if 2) What will happen to system (student and cart) if the students suddenly stops?the students suddenly stops?3) Is it possible to calculate the moment of the 3) Is it possible to calculate the moment of the system if so how?system if so how?4) Does the momentum of the system change?4) Does the momentum of the system change?5) What causes the momentum of the system to 5) What causes the momentum of the system to change?change?

Demo Explanation:Demo Explanation:

Demo: Stuck in SpaceDemo: Stuck in Space

You are stuck in space so that you back is against the Earth. What can you do to turn around? Sit on a swivel chair and find out.

Collisions: Sample Problem 1: Two space people collide and bounce off of each other. Find the square guys momentum:

Sample Problem 2: Find the orange balls final velocity:

Sample Problem 3: Find the velocity of Sample Problem 3: Find the velocity of the blue ball so that when the object the blue ball so that when the object collide and stick they have a combine collide and stick they have a combine velocity of -40m/s.velocity of -40m/s.

Sample problem 4: Sample problem 4:

A 50,000 kg cannon fires a 30 kg shell with a velocity of 400 m/s. If the cannon is on wheels, find its recoil velocity:

Sample Problem 5: Sample Problem 5: Two astronauts Two astronauts are moving with a velocity of 25m/s and are moving with a velocity of 25m/s and push off of each other so astronaut A push off of each other so astronaut A has a velocity of zero. If astronaut A has has a velocity of zero. If astronaut A has a mass of 90kg and astronaut B has a a mass of 90kg and astronaut B has a mass of 100kg, find the velocity of B. mass of 100kg, find the velocity of B.

Go to Practice WorksheetGo to Practice Worksheet

Extra DemonstrationsExtra Demonstrations

Demo: Pass the rice bag.Demo: Pass the rice bag.1) What will happen to the system as rice bag 1) What will happen to the system as rice bag is passed back and forth.is passed back and forth.Hint: Think of the total momentum of the Hint: Think of the total momentum of the system.system.

Demo: Demo: 1) Who will travel the fastest?1) Who will travel the fastest?2) When the line is completely 2) When the line is completely stretched, which way will they budge?stretched, which way will they budge?

Space Shuttle Main Engine: Space Shuttle Main Engine: Propulsion and MomentumPropulsion and Momentum

Converging Diverging Converging Diverging Nozzle Nozzle