Chapter 7 Conservation of Linear and Angular Momentum

*How is the word "conservation" used in the context of physics discussions?

page 7-2 Conservation of Linear Momentum

make a sketch similar to Figure 6-3. Let object B have a larger mass than object A.

page 7-3 Why is the velocity vector for A in the opposite direction compared to the velocity vector for B?

What questions do you have on equation 3?

Suppose V_A is 7 meters/second to the left. Write down some fact for V_B .

Linear momentum p = mV This calculates the momentum for a single object.

The total linear momentum for a system of particles is p = Σ m_iV_i

Suppose object A (4kg) has a velocity of 3 meters/second to the right. Suppose object B (5kg) has a velocity of 8 meters/second to the right. Calculate the total linear momentum of this system.

Suppose object A (4kg) has a velocity of 3 meters/second to the left. Suppose object B (5kg) has a velocity of 8 meters/second to the right. Calculate the total linear momentum of this system.

What is the total linear momentum of the two carts on an air track before the spring is allowed to expand?

Conservation of Linear Momentum: If no net external force acts on a system then the total linear momentum of the system is conserved.

On an air track we can ignore friction. Can we ignore the force of gravity? Why don’t the carts fall to the floor? Is the net external force zero?

Does the spring apply an external or internal force to the system?

What is the total linear momentum after the spring is allowed to expand?

Suppose cart A has a mass of 0.3kg and cart B has a mass of 0.6 kg. Suppose that the velocity of cart A after the spring expands is 1.8 m/s to the left. Calculate the velocity of cart B.

page 7-4 Collision Experiments

Is linear momentum conserved in many collision experiments?

What condition is required such that we can use the principle of conservation of linear momentum to work problems?

Does linear momentum have X and Y components?

What questions do you have on page 7-5?

What is true regarding the value of the momentum carried into the collision and the value of the momentum carried out of the collision?

We will calculate the momentum in and out using Figures 5 a,b on page 7-6.

page 7-7 Subatomic Collisions

Example 1 Rifle and Bullet

What questions do you have on this example?

page 7-8 What questions do you have on Example 2?

We will work the exercises on page 7-8

page 7-9 Conservation of Angular Momentum

Watch the Cons_L movie that is on your CDROM in the Movies folder.

Try to observe the direction of rotation of the wheel and the person.

What sports make great illustrations of Conservation of Angular Momentum?

Demo I will perform the demonstration drawn in Figure 8.

Demo I will try to perform the demonstration discussed on page 7-10 and drawn on page 7-11.

I will use L to represent angular momentum. The magnitude is: L = mvr .

You should work exercise 8. Measure the distance between images of the object on the outer circle. Measure the radius of the outer circle. Repeat these measurements for the images (three images) near the center of the circle.

Neglecting the mass of the spokes and axle, what is the angular momentum of a bicycle wheel that has a mass of 3 kg and a radius of 20 inches if the wheel spins once every 2 seconds?

page 7-12 A More General Definition of Angular Momentum

How does the text define "lever arm?"

Demo We will try to perform the two demonstrations drawn on page 7-13.

You should answer the question in Figure 12 before class.

page 7-14 Angular Momentum as a Vector

Is linear momentum a vector?

Is angular momentum a vector?

Is the direction of the velocity constant for the case of an object moving in uniform circular motion?

What is the direction of the angular momentum vector?

L is a vector. Why is the addition shown in equation 15 legal?

Demo We will see demonstrations of Figure 15 and 15b.

L will be called positive when it is pointing up in our classroom.

page 7-16

Before you come to class, try to predict the outcome of the demonstrations in Figure 16b and 16c.

Watch the Cons_L movie that is on your CDROM in the Movies folder.

Copyright© 2001 - 2006 by Greg Clements Permission is granted to reproduce this document as long as 1) this copyright notice is included, 2) no charge above photocopy costs is made, and, 3) the use is for an educational purpose. Editing of the document to suit your own class style and purposes is allowed.