1. Chapter 10
Section 3

2. Momentum 3
Mass and Inertia
The mass of an object is the amount of matter in the object.
In SI units, the unit for mass is the kilogram.
The weight of an object is related to the object's mass.

3. Momentum 3
Mass and Inertia
Objects with more mass weigh more than objects with less mass.
However, the size of an object is not the same as the mass of the object.

4. Momentum 3
Mass and Inertia
The more mass an object has, the harder it is to start it moving, slow it down, speed it up, or turn it.
This tendency of an object to resist a change in its motion is called inertia.
Objects with more mass have more inertia.

5. Momentum is usually symbolized by p.3
Momentum
The momentum of an object is a measure of how hard it is to stop the object, and it depends on the object's mass and velocity.
Momentum is usually symbolized by p.

6. Momentum 3
Momentum
Mass is measured in kilograms and velocity has units of meters per second, so momentum has units of kilograms multiplied by meters per second (kg . m/s).
Momentum has a direction that is the same as the direction of the velocity.

7. Conservation of Momentum 3
Conservation of Momentum
According to the law of conservation of momentum, the total momentum of objects that collide is the same before and after the collision.
This is true for the collisions of billiard balls, as well as for collisions of atoms, cars, football players, or any other matter.

8. Using Momentum Conservation 3
Using Momentum Conservation
There are many ways that collisions can occur.
Sometimes, the objects that collide will bounce off of each other.
In other collisions, objects will stick to each other after the collisions.
In both of these types of collisions, the law of conservation of momentum enables the speeds of the objects after the collisions to be calculated.

9. Imagine being on skates when someone throws a backpack to you.
Momentum 3
Sticking Together
Imagine being on skates when someone throws a backpack to you.
Before the student on skates and the backpack collide, she is not moving.

10. Momentum 3
Sticking Together

11. Supposed a 2-kg backpack is tossed at a speed of 5 m/s.
Momentum 3
Sticking Together
Supposed a 2-kg backpack is tossed at a speed of 5 m/s.
Your mass is 48 kg, and initially you are at rest.
Then the total initial momentum is

12. You can use the equation for momentum to find the final velocity.3
Sticking Together
After the collision, the total momentum remains the same, and only one object is moving.
You can use the equation for momentum to find the final velocity.

13. Colliding and Bouncing Off
Momentum 3
Colliding and Bouncing Off
Supposed two identical objects moving with the same speed collide head on and bounce off.
Before the collision, the momentum of each object is the same, but in opposite direction.
So the total momentum before the collision is zero.
Click here to view movie.

14. Colliding and Bouncing Off
Momentum 3
Colliding and Bouncing Off
If momentum is conserved, the total momentum after the collision must be zero also.
This means that the two objects must move in opposite directions with the same speed after the collision.

15. Section Check 3
Question 1
An object’s momentum can be increased either by increasing its _______ or its _______.

16. Section Check 3
Answer
The answer is mass or velocity. A thrown baseball is harder to stop than a thrown ping-pong ball. At the same time, a baseball thrown by a professional pitcher is harder to stop than the same baseball lobbed by a fan.

17. Question 2 Answer 3 Explain the law of conservation of momentum.
Section Check 3
Question 2
Explain the law of conservation of momentum.
Answer
This law says that the total momentum of objects in collision is always the same after the collision as it was before the collision.

18. Section Check 3
Question 3
Two objects of the same mass are moving directly toward each other at the same speed. What is the total momentum of the two objects?
Answer
The total momentum is zero. This will be the same after the collision as well.