Physics Lesson 11/3

Physics Lesson 11/3

Inclined Planes

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Inclined Planes

How do we determine forces on an inclined plane?

Inclined Planes

• We have applied Newton's Laws to a variety of situations, but only to motions that were were either horizontal or vertical.

• How would you apply Newton's Laws to a person sliding down a slide?

• How would you determine the net force acting upon the person sliding?

Inclined Planes

• First, determine the forces acing on the system. (In this case the girl is the system)

• The gravitational force on the girl is downward, toward the center of Earth.

• The normal force acts perpendicular to the slide.

• The girl's acceleration would be along the slide.

Choosing a Coordinate System

• You should nex choose your coordinate system carefully.

• Because the girl's acceleration is parallel to the incline, one axis, the x-axis should be in that direction.

• The y-axis is always perpendicular to the x-axis, so it is perpendicular to the incline's surface.

Choosing a Coordinate System

• With this coordinate system, you now have two forces, the normal force, and the friction force, in the direction of the coordinate axes.

• The weight, however, has components in both the x- and y- directions.

• This means that when you place an object on an inclined plane, the magnitude of the normal force between the object and the plane usually will not equal the object's weight.

Choosing a coordinate system

• You will need to apply Newton's Laws once int the x- direction, and once in the y-direction.

• Because the weight does not point in either of these directions, you will need to break this vector into it's x and y components before you can sum the forces in these two directions.

Fill in the Blanks

Example Problem - A 562N crate is resting on a plane inclined 30.0 degrees above the horizontal. Find the components of the crate's weight that are parallel and perpendicular to the plane.

Fill in the Blanks

Example Problem - A kid has a mass of 45kg. He is going down a slide sloped at 27 degrees. The coefficient of kinetic friction is 0.23. How fast doe he slide 1.0 s after starting from rest?

Practice Problems

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Exit Ticket - What is

 $\phi$  ?