Please help, simple question

[Atlantic]

I am analyzing an object sliding down a hill.

 

I have the gravitational potential energy, gravitational force, Net Force (moving down the hill), acceleration, mass, normal force (on sloped surfaces, that is on the "Y" axis.....i think).

 

How do i find out the force due to friction.

Right now all I did was subtract the net force from force due to gravity(mg=F), and got a number. Is that number the force due to friction, if not, how can i find it.

 

Thanks in advance.

[Neurocomp2003]

your way is not correct becuase your forces are not aligned

you can do this with Energy equations however but not forces becasue forces are vectors and rely on alignment

 

 

ok your gonna be setting up a "FORCE" Diagram or whatever it is called

 

the mass/gravity FOrce points down, F_g

the normal Force perpendicular to motion (perd. to incline) F_n

the friction Force parallel to incline going up. F_f

and if there was an initial force/acc/velo. F_i

 

set your diagrm up with these for diagrams and use your knowledge of trigonometry(cos/sin) to align these force

you'll end up with 2 equations. THe best alignment is to

align with respect to X,Y axis but you can also align with

incline/normal axis if you choose

[Atlantic]

F_n = F_g cos(theta)

 

theta is the elevation of the hill bottom>up.

The equation i know for sure works, but i don't know if i can use it on finding friction.

 

Can it?

 

Here is the picture i did in pain, lets you see what i'm thinking........... attachment

[JaKiri]

Friction = :mu:mgcos:lctheta:

 

Friction is defined as having a maximum of the reaction force ('R') multiplied by the coefficient of friction (':mu:')

 

The normal reaction (ie the force perpendicular to the plane) will be equal and opposite to the component of gravity in that plane (obviously; the object doesn't fly off the plane, or through it, so there must be no resultant force).

 

R = mgcos:lctheta: (a simple way to remember wheterh it's sin or cos is to decrease the angle to 0, and if the multiple you'd get is 0 it'll be sin, 1 it'll be cos).

 

F_R = :mu:R

 

= :mu: mg cos :lctheta:, as above.