# I Friction under material

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1. Aug 12, 2016

### Gerryf

This is a question about friction and grip .

The set up is as follows ,-
We have a non yielding ,consistent surface (x) fixed to a work bench . Next we have a removable lever arm made of a non flexible material and about 75 cm long .

Fixed to the underside of one end of the lever arm we have a a non flexible plate which has an under surface made of rubber . The plate is circular , has a hole at its center and has a surface area of 100 cm sq. The lever arm itself does not touch the material x .

Next ,via a bolt placed through the hole in the center of the plate and through the non yielding material we pivot-ably secure the lever arm to surface x so that the rubber lies on top of the surface x .

The lever arm extends beyond the work bench and a force of 100 newtons is vertically applied to the plate so that the rubber is pressed against the surface x with a constant force .

When the lever arm is moved the rubber covered plate rotates about the bolt axis in a rotational fashion and a given force ,F1 , is required to keep the lever arm moving .

That's the set up .

The question is as follows -

A portion of the rubber covered plate,20cm sq is removed by making a cut across the plate at right angles to the lever arm and this is reattached to the system by a lever arm extension so that the cut surfaces of the two sections of the original plate are parallel and 5 cm apart . (that is the rubber plate is now in two sections the first as it was and rotating about the bolt and the second section now at a greater distance from the pivot point .

The question is -would greater force be required to get the lever arm moving against inertial frictional forces in this new system than in the original set up and would greater force be required to keep the system moving ?

Thanks
Gerry

2. Aug 12, 2016

### Gerryf

If it helps in the understanding of the problem here is the context . The plate represents the area in of the foot in contact with the ground after the heel leaves the ground . The whole plate represents the ball of the foot the toes in a curled position and the split plate represents a situation where the toes are extended .

The question is does the planted foot resist rotation and slipping more with the toes curled or extended and to the best of my knowledge has not been asked or answered until now .

Gerry

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