Friction and Forces on Inclined Planes

The Normal Force The normal force is the supporting force that acts on the object perpendicular to the surface plane. It’s the portion of the weight of the object that is supported.

Notice how in all cases, the coefficient is lower for sliding friction than static friction. This means it’s easier to keep an object moving on a surface than it is to get it going in the first place.

10 kg Force of push = ? N μ s = 0.85 μ k = 0.55 Static friction kinetic friction How much force does it require to get the box moving? How much force does it require to accelerate the box at 5 m/s 2 ?

10 kg Force of push = ? N μ s = 0.85 Static friction F s = 0.85 (mg) F s = 0.85 (10)(9.8) F s = 83.3 N So, it takes a force of at least a force of 83.3 N to overcome the static frictional force and get the box moving. Static friction

10 kg Force of push = N μ k = 0.55 Kinetic friction F k = 0.55 (mg) F k = 0.55 (10)(9.8) F k = 53.9 N F push - F kinetic friction = F net F push – 53.9 N = 10 (5) N

Looking at the Frictionless Forces on an Inclined Plane

A 20 kg. box slides down a frictionless inclined plane of 35 degrees. What is it’s acceleration?

Looking at the Frictional Forces on an Inclined Plane

A 20 kg. wooden box slides down a wood inclined plane of 35 degrees. What is it’s acceleration?

When you push on a 5 kg. object on a flat surface with a force of 100 N the acceleration of the object is 13 m/s 2. What is the coefficient of kinetic friction between the object and the surface?