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You have to break the bonds either way, be it lifting the object or moving it. Why is it that we don’t have to overcome the force required to break the cluster of molecules?

xray0
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A J
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    Note that most of the frictional force is caused by the unevenness of the surfaces. When the bumps collide, either they deform or give the effect of dragging one of the objects up an inclined plane: both of these things require extra force. – David Richerby Jul 31 '16 at 13:57

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It does!

In most cases the force is too small to be noticable however it is there. I spent a happy few months measuring the friction between carbon whiskers, and the adhesion force between the whiskers was large enough to cause a noticable deformation of the whiskers when I separated them. In fact you had to add the adhesion force to the applied load to get a correct value for the friction coefficient.

For large objects the force is usually small compared to the weight of the object however in special cases, e.g. very clean surfaces, it is large enough to cause cold welding.

John Rennie
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If you have an object sitting on a table, what's actually happening on the atomic scale is the electrons of the atoms on the table are repelling the electrons on the surface of the object. The object is basically hovering over the table (but only be a very tiny amount). Therefore, when you lift an object off a table, you don't normally have to overcome any kind of intermolecular force, except if the surfaces are attracted by some forces (which could for e.g. be magnetic, electrostatic, an air layer as in suction cups)

PhysLab
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  • With this argumentation, friction would not exist at all... – Steeven Jul 31 '16 at 07:42
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    @Steeven I disagree. Friction comes in part from the object and table not being perfectly smooth. This means that, when you drag an object across the table, the bumps come into contact with each other and must either be deformed or cause the object to be lifted slightly. Both of these require work, even if the object is viewed as hovering slightly above the table (as long as the bumps are bigger than the hover height, which thye surely would be). – David Richerby Jul 31 '16 at 09:59