1. Forces and Friction

2. The weight of an object depends on the strength of gravity wherever the object is. The mass always stays the same.

3. Weight F w = mg Gravity (9.8 m/sec 2 ) Mass (kg) Weight force (N)

4. 6.1 Calculate weight How much would a person who weighs 490 N (110 lbs) on Earth weigh on Jupiter? The value of g at the top of Jupiter’s atmosphere is 23 N/kg. (Since Jupiter may not actually have a surface, “on” means at the top of the atmosphere.)

5. Calculate force A 10-kilogram ball is supported at the end of a rope. How much force (tension) is in the rope?

6. Friction Friction results from relative motion between objects. Frictional forces are forces that resist or oppose motion.

7. Friction F f =  F n Normal force (N) Coefficient of friction Friction force (N)

8. Calculate force of friction A 10 N force pushes down on a box that weighs 100 N. As the box is pushed horizontally, the coefficient of sliding friction is 0.25. Determine the force of friction resisting the motion.

9. Sliding Friction F f =  s F n Normal force (N) Coefficient of sliding friction Friction force (N)

10. Table of friction coefficients

11. Calculate using friction The engine applies a forward force of 1,000 newtons to a 500-kg car. Find the acceleration of the car if the coefficient of rolling friction is 0.07.