1. Activity 80: Newton’s Laws of Motion

2. Newton’s Laws of Motion Challenge: What relationships between force and motion did Newton discover? Key Vocabulary:  Balanced forces  Unbalanced Forces  Friction  Net force

3. Getting Started  Read the introduction on page 29.  Remember that a force is a push or pull.  Complete the Before column for the “Anticipation Guide: Laws of Motion”  Let’s get started

4. Stopping to Think #1  The heavy ball has more inertia because it would take more force to change its motion than the light one

5. Stopping to think #2  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

6. Stopping to Think #3  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.

7. Stopping to Think #4  Yes, because the ratio of force to mass could be the same for the two situations. For example, the acceleration of 44 N/100 kg is the same as 4 N/1 kg.

8. Stopping the Think #5  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 applies simultaneously.

9. Vocabulary Review  Friction  The force that exists at the boundary between any two pieces of matter  Net force  The combined force acting on a system  Balanced force  When all of the forces acting on an object equals zero, there is no movement  Unbalanced forces  When all of the forces on an object do not equal zero; there is movement

10. Answers to the Anticipation Guide

11. Analysis Questions 1, 3-5 in your notebooks. (#2 will be a graded UC Assessment ) 1. Because there is no friction in outer space, an object in motion remains in motion. Once a shuttle leaves the Earth’s atmosphere, it needs very little fuel to get to its destination. It uses fuel to change direction (thrusters) or to land.

12. 3.a. A 1,000 kg car

13. 3b. A 2,000 kg car F = ma 1,000 N = 2,000 kg × a a = 1,000N / 2,000 kg a = 0.5 m/s

14. 4. 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 (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

15. 5. People spend money on lubricants because they reduce friction and less friction means that the engine and the wheels move more smoothly (and stay cooler). This means that the engine needs to exert less force, which often results in it lasting longer, using less fuel, and requiring fewer repairs.