1. Final Exam Review Newton’s Laws Friction & Weight

2. Newton’s 1 st Law Objects in motion stay in motion and objects at rest stay at rest unless a force acts on it. (Law of Inertia)

3. Example The meteor in Armageddon would have continued toward the Earth unless Ben and Bruce blew it off course. (Applied a net force to change it’s motion)

4. Newton’s 2 nd Law F = ma Key Point: A net force will change the velocity or direction of motion of an object.

5. Example Roberto and Laura are studying across from each other at a wide table. Laura slides a 2.2kg book toward Roberto. If the net force acting on the book is 1.6N, what is the book’s acceleration?

6. Example Roberto and Laura are studying across from each other at a wide table. Laura slides a 2.2kg book toward Roberto. If the net force acting on the book is 1.6N, what is the book’s acceleration? Givens m = 2.2 kg F = 1.6 N

7. Example Roberto and Laura are studying across from each other at a wide table. Laura slides a 2.2kg book toward Roberto. If the net force acting on the book is 1.6N, what is the book’s acceleration? Givens m = 2.2 kg F = 1.6 N F = ma → 1.6N = (2.2kg)a a = 0.73 m/s 2

8. Practice Pg 132- Practice C

9. Newton’s 3 rd Law “Every action has an equal and opposite reaction” Forces come in pairs.

10. Weight Def: Force of gravity on an object’s mass. If “g” changes, so does weight. You “weigh” less on Mars, because g= 3.7 m/s 2 there instead of 9.8 m/s 2 like Earth. Earth Mars BIG SMALL

11. Example Determine the weight of a 150kg man on the surface of the earth. F = ma F = (150kg)(9.8m/s 2 ) = 1470N

12. Practice Determine the weight of the 150kg person on the following planets: PlanetGravity Mercury3.6 m/s 2 Venus8.6 m/s 2 Jupiter25.9 m/s 2 Saturn11.3 m/s 2

13. Friction Def: The force that resists motion between two objects in contact together. Formula: F f = μF n Examples: Sliding friction (box on floor) Air resistance (falling objects) Water resistance (swimming)

14. Example A 24kg crate initially at rest on a horizontal floor requires a 75N horizontal force to set it in motion. Find the coefficient of static friction between the crate and the floor.

15. Example A 24kg crate initially at rest on a horizontal floor requires a 75N horizontal force to set it in motion. Find the coefficient of static friction between the crate and the floor. Givens F f = 75N m = 24kg F n = ?

16. Example A 24kg crate initially at rest on a horizontal floor requires a 75N horizontal force to set it in motion. Find the coefficient of static friction between the crate and the floor. Givens F f = 75N m = 24kg F n = ? F n = mg = (24kg)(9.8m/s 2 ) = 235N F f = μF n → 75N = μ(235N) μ = 0.32

17. Practice Pg 139- Practice D Problem 2