Forces and Friction The weight of an object

Forces and Friction

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

Weight force (N) Fw = mg Gravity (9. 8 m/sec 2) Mass (kg)

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. )

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

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

Friction force (N) Ff = m Fn Normal force (N) Coefficient of friction

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.

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

Table of friction coefficients

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.