AP Physics C 2017

Figure  10.5b           Forces  acting  on  the block   in  Figure  10.4    ,   with    the weight  vector  resolved    into

components  that    line    up  with    the friction    force   and the normal  force.

Memorize this

As  a   rule    of  thumb,  in  virtually   all inclined-plane  problems,   you can always  break   the weight

vector  into    components  parallel    and perpendicular   to  the plane,  where   the component   parallel    to

(pointing   down)   the plane   =   mg(sin  θ)  and the component   perpendicular   to  the plane   =   mg(cos  θ).

This rule always works, as long as the angle of the plane is measured from the horizontal.

Even Physics C Students Must Use Free-Body Diagrams

It must be emphasized that even Physics C students must go through the four-step problem-solving process
described in this chapter. Frequently, Physics C students try to take shortcuts, thinking that equilibrium
problems are easy, only to miss something important. If free-body diagrams are good enough for
professional physicists to use, they are good enough for you.

Torque

Torque occurs when a force is applied to an object, and that force can cause the object to rotate.

Torque =    Fd

In other words, the torque exerted on an object equals the force exerted on that object (F ) multiplied by
the distance between where the force is applied and the fulcrum (d ) as long as the force acts
perpendicular to the object.

Fulcrum: The    point   about   which   an  object  rotates

Figure 10.6 shows what we mean: