sliding block on ramp

poikonen03

There is a block of W Newtons and a ramp is A degrees above the horizontal. At this angle the block begins to slide. How do I find the force of friction and then it should be quite easy to find coefficient of friction. (I already have already solve for the normal force Fw and the force parallel the ramp Fp)?

OlderDan

If you solved for the normal force, you were very close to finding the component of gravitational force parallel to the plane. Friction overcomes (equals in magnitude) that force for small angles. When the block begins to slide, friction has just been overcome. At that critical angle, the component of gravity parallel to the plane equals the force of friction.

Once sliding starts, the frictional force gets smaller and there is some acceleration. To find the frictional force when the block is sliding, reduce the angle to achieve constant velocity after you give the block a little push to get it started.

poikonen03

so basically F sub P (force parallel to ramp) = F sub F (force of friction) since there is no accel...so F sub N (normal force) * Coefficient of Friction = F sub F
thanks