# 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.