# What is the force of friction on the body? [duplicate]

This might seem like a stupid question, but my instructor could not give a straightforward answer.

If a body is kept in contact with a completely vertical surface i.e. right angle to the ground, and only force on the body is the force of gravity straight downwards.Then normal force on the body would be zero. We know that frictional force on the body is proportional to the normal force, hence it is also zero. Does that mean there is no friction whatsoever, despite the surface rubbing?

## marked as duplicate by sammy gerbil, ZeroTheHero, M. Enns, Buzz, John Rennie newtonian-mechanics StackExchange.ready(function() { if (StackExchange.options.isMobile) return; $('.dupe-hammer-message-hover:not(.hover-bound)').each(function() { var$hover = $(this).addClass('hover-bound'),$msg = $hover.siblings('.dupe-hammer-message');$hover.hover( function() { $hover.showInfoMessage('', { messageElement:$msg.clone().show(), transient: false, position: { my: 'bottom left', at: 'top center', offsetTop: -7 }, dismissable: false, relativeToBody: true }); }, function() { StackExchange.helpers.removeMessages(); } ); }); }); Jan 12 at 9:42

Of course this is not obtainable in the real world. Surface irregularities will cause variations in the way the two surfaces come in contact and interact. This could even result in the object losing contact with the vertical surface altogether. The friction model of $$f=\mu N$$ is a very simplified model, and one instance it breaks down is in scenarios where the force between the two objects is hard to define. This is such a case.