1. Analysis question #2 is due tomorrow
Do Now for 5/6/13
Take out E80
HW: Test on Wednesday
Analysis question #2 is due tomorrow

2. E80 Newton’s Laws of Motion
Today’s Target: I will be able to state the three laws of motion that Newton discovered.
Review reading
Answer Stopping to Think Questions
Analysis Questions
Analysis #2

3. E80 Newton’s Laws of Motion
1. Which has more inertia, a heavy ball or a light ball rolling at the same speed in the same direction?
Think about which one is more resistant to a change in motion.
The heavy ball has more inertia because it would take more force to change its motion than the light one.

4. E80 Newton’s Laws of Motion
2. What would happen to a baseball if you could throw it in outer space? Explain in terms of inertia and friction.
Without friction, a thrown baseball would continue in a straight line at a constant speed forever, or until it encountered another force that changes its motion.

5. E80 Newton’s Laws of Motion
3. A car travels along a straight road at a steady 40 MPH. Are the forces on the car balanced or unbalanced?
Explain.
The forces are balanced. The frictional forces within the car and from the road are balanced by the equal but opposite force applied by the engine. The net force is zero, and the car travels with constant speed and direction.

6. E80 Newton’s Laws of Motion
4. Can a light object that is hit with a small force accelerate as rapidly as a heavier object hit with a big force? Why or why not?
Yes, because the ratio of force to mass could be the same for the two situations. For example, the acceleration of 400 newtons/100 kg is the same as 4 newtons/1 kg.

7. E80 Newton’s Laws of Motion
5. If you hold a backpack in your hand, the force of gravity pulls it downward. What force keeps it from falling to the ground?
The “reaction” force is your hand that applies an equal and opposite force on the backpack. However, it is impossible to say which of the two forces is the “action” and which is the “reaction” since they are applied simultaneously.

8. E80 Newton’s Laws of Motion
1. Spaceships that travel millions of miles into outer space use very little fuel. How can they go so far on so little fuel?
Because there is no friction in outer space, an object in motion remains in motion. Once a space probe leaves behind the friction of Earth’s atmosphere, it needs very little fuel to get it to its final destination. (However, it uses fuel to slow down if it is going to land on a planet or to change direction.)

9. E80 Newton’s Laws of Motion
2. Use Newton’s Laws to explain why it is easier to turn a truck when it is empty than when it is carrying a heavy load.

10. E80 Newton’s Laws of Motion
3. An engine can exert a force of 1,000 newtons. How fast can this engine accelerate:
a. a 1,000 kg car
F = m x a
1,000 N = 1,000 kg x a
a = 1,000 N/1,000 kg
a = 1 m/s2

11. E80 Newton’s Laws of Motion
b. a 2,000 kg car
F = m x a
1,000 N = 2,000 kg x a
a = 1,000 N/2,000 kg
a = 0.5 m/s2

12. E80 Newton’s Laws of Motion
4. Use Newton’s third law to explain why a blown up, but untied balloon flies around the room when you let it go.
Newton’s third law states that forces come in equal and opposite pairs. For every action force there is an equal and opposite reaction force. The balloon exerts a force on the air (the action force), causing the air to rush out the opening, while at the same time the air exerts an equal and opposite reaction force on the balloon, causing the balloon to fly around the room.

13. E80 Newton’s Laws of Motion
5. Motor oil, axle grease, and other lubricants are slippery. Why do you think people spend the money to put these lubricants in their cars?
Lubricants reduce friction, and less friction means that the engine and the wheels move more smoothly (and stay cooler). This means the engine needs to exert less force, which often results in it lasting longer, using less fuel, and requiring fewer repairs.

14. E80 Newton’s Laws of Motion – Key Points
1. An object that is not being subject to a force will continue to move at a constant speed in a straight line.
2. Friction is a force that causes changes in the speed of an object’s motion.
3. The magnitude of the change in motion can be calculated using the relationship
F = ma, which is independent of the nature of the force.
4. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

15. E80 Newton’s Laws of Motion
Complete sheet 80.1