Static friction preventing block from sliding

AI Thread Summary
The discussion focuses on calculating the minimum force required to prevent a block from sliding down an incline with a static friction coefficient of 0.3. The participants clarify the forces acting on the block, including gravitational force and frictional force, and emphasize the importance of setting the sum of these forces to zero for static equilibrium. Key equations involved include the gravitational force component down the incline (mgsinθ) and the frictional force (μmgcosθ). The final formula derived indicates that the applied force must exceed the difference between the gravitational force and the frictional force to maintain static conditions. The conversation highlights the need for a clear understanding of force components and equilibrium conditions in solving the problem.
malta
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Homework Statement



If the coefficient os static friction between the incline and block is .3, then what is the minimum force,F, needed to prevent the block from sliding?
m=20kg theta= 50 degrees

Homework Equations



Normal force= mgcosx
Fs= uk mgcosx

The Attempt at a Solution



I know how to solve this this for the perpendicular force (up the ramp) but I can't seem to figure out how to do it for thr parallel force.
 
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malta said:

Homework Statement



If the coefficient os static friction between the incline and block is .3, then what is the minimum force,F, needed to prevent the block from sliding?
m=20kg theta= 50 degrees

Homework Equations



Normal force= mgcosx
Fs= uk mgcosx

The Attempt at a Solution



I know how to solve this this for the perpendicular force (up the ramp) but I can't seem to figure out how to do it for thr parallel force.

I assume that you drew yourself a diagram with a coordinate system that has its x-axis parallel to the inclined plane and its y-axis perpendicular to the plane. Then, what is the force due to gravity acting to move the block down the plane? What is the frictional force acting to oppose the motion down the plane? What is the condition on the sum of all forces along the plane so that the block does not move?
 
Fore due to gravity is mgsinx and the frictional force = (coefficient of fiction)(mgCosx)
And the condition on all forces along the plane so that the block doesn't move has to equal to zero

But I can't seem to get what to set equal to what
 
Last edited:
anyone? I am doing a test review for a test tomorrow so this would greatly help me
 
malta said:
Fore due to gravity is mgsinx and the frictional force = (coefficient of fiction)(mgCosx)
And the condition on all forces along the plane so that the block doesn't move has to equal to zero

But I can't seem to get what to set equal to what

You have the right parts.

Draw a diagram and add the forces that need to make it be static.
 
ok so
F + mgcosx= N
(friction)N= mgSinx

So F = (mgSinx)/(friction) - mgCosx

There we go, thanks again
 
malta said:
ok so
F + mgcosx= N
(friction)N= mgSinx

So F = (mgSinx)/(friction) - mgCosx

There we go, thanks again

Not exactly.

F + μmgcosθ = mgsinθ

You only need to supply force in excess of what friction alone will not.
 

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