Forces: Friction and Tension

1. Forces: Friction and Tension

2. The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it. • Opposes motion What is Friction?

3. The amount of friction between two surfaces depends on two factors • The kinds of surfaces • The force pressing the surfaces together • Friction is caused by the rough surfaces of objects • ALL objects have a rough surface, even if it’s only on a microscopic level Friction

4. Static Friction= the frictional force that prevents two surfaces from sliding past each other • The reason its harder to start pushing than to continue pushing the same object • Kinetic Friction= when two objects are moving relative to each other and rub together (like a sled on the ground) • Sliding Friction=the frictional force that opposes the option of two objects sliding past each other • Rolling Friction=frictional force between a rolling object and the surface it rolls on Types of Friction

5. The maximum amount of friction force that a surface can exert upon an object can be calculated using the formula below: • Ff= µFN • µ is the coefficient of friction • The value of μ provides a measure of the relative amount of adhesion or attraction of the two surfaces for each other. • The more that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force. Friction

6. Fg=weight=mg • Ff=µFN • Fnet=FA + (-Ff) Friction

7. A desk has a mass of 2.5 kilograms. If the coefficient of static friction between the desk and the floor is 0.04, what force must be used to move the desk from rest? • What force must be used to keep it moving at a constant velocity if the coefficient of kinetic friction is 0.0267? Friction