1. Why do people “skip” more when they walk on the moon versus when they walk on Earth?

3. Objectives Define force. Explain Newton’s laws. Apply Newton’s laws to solve problems.

4. What is a force? An object that experiences a push or pull has a force exerted on it. Have both magnitude and direction Forces acting upon an object can be added using vector addition to find the net force.

5. Newton’s First Law An object at rest will stay at rest, and an object that is moving will continue to move in a straight line with constant speed, if and only if the net force acting on that object is zero.

6. Newton’s Second Law Acceleration of a system equals the net force acting on it, divided by its mass.

7. Let’s practice! So Ms. Carlin weighs 165 lbs (on a good day), which is 734 N. What is Ms. Carlin’s mass? What is your mass? How many pounds in 1 Newton? The answer is 0.225.

8. Newton’s Third Law Two forces that make up an interaction pair of forces are equal in magnitude, but opposite in direction and act on different objects.

9. IN Question! Give an example of Newton’s Second Law. New rule: NO empty seats in the front of the classroom

10. Inertia Newtons First Law is sometimes called Law of Inertia Inertia is the tendency of an object to resist change.

11. Free Body Diagram Physical model that represents the forces acting on a system. Helps show the vectors of each of the forces!

12. Normal force Perpendicular contact force exerted by a surface on another object.

13. Draw the free-body diagram A flowerpot falls freely from a windowsill. A cable pulls a crate across a horizontal surface. A rope lifts a bucket at a constant speed. A rope lowers a bucket at a constant speed.

14. Practice Problems! Two horizontal forces, 225 N and 165 N, are exerted on a canoe. If these forces are applied in the same direction, find the horizontal force. If the same two forces are exerted on the canoe in opposite directions, what is the net horizontal force?

15. More practice 4.2 Section Review