B Force and friction

1. May 21, 2016

Sachin Saraogi

We know that force * coeff. of friction = m * g. . It does not make sense. Pls read details. This is when force is applied perpendicular to the direction of friction. But suppose we say that m = 10 kg, g = 10 m/s2, coeff. of friction is 0.1. Then by formula it says that force required to keep the object against the wall will be 1000 N. How does this make sense? I mean the force required to lift the object without any support is just m*g = 100 N. Pls explain this so that it makes intuitive sense......

2. May 21, 2016

Simon Bridge

Of course it doesn't, it is nonsense.

This is not correct ... the usual equation is $F=\mu N$ where "N" is the magnitude of the contact force between the surfaces.
Where that is a horizontal flat surface, $N=mg$ ... which is to say it's the weight of the object.

Oh you mean that you are applying the normal force?

If you want friction to hold a box against it's weight, on a wall that slippery, then sure ... you will need a lot of force... especially if you are only applying the force horizontally.