Force and Motion in Two Dimensions

5.3Page 131

Friction at 90°

• When friction acts between two surfaces, you must take into account both the frictional force that is parallel to the surface and the normal force that is perpendicular to it.

• So far, we have considered only the motion along a level surface.

• Now we will analyze situation in which the forces acting on an object are at angles or the than 90°.

Remember!!

• When the net force on an object is zero, the object is in equilibrium.

• Equilibrium can occur no matter how many forces act on an object as long as the resultant is zero, the net force is zero and the object is in equilibrium!

• What is the net force acting on the object?

What is the sum of the forces exerted does not equal zero?

• Add the two forces already being exerted on the object. This equals the resultant force.

• The equilibrant is the force that has the same magnitude but is in the opposite direction of the resultant.

Motion on an Inclined Plane

1. Identify the forces acting on the object

2. Sketch a free-body diagram.

3. Gravity is in the downward direction

4. Normal force is perpendicular.

5. Friction is opposite of motion.