Are formed where bumps from two surfaces come into contact.

the answer is Friction.

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Micro welds are formed where bumps from two surfaces come into contact.

Explanation:

The surface of all existing objects or elements, have some bumps and dips. Whenever the surfaces of two different bodies with bumps and dips come into contact with each other, sticking occur.

This causes the production of micro welds between the two surfaces that inhibit the smooth motion. These micro welds create a static force that opposes the smooth motion between the surfaces. This is called “friction”.

This friction force can be stopped only when it can either be dominated with the equal opposite force or inhibited with lubricating agents that reduce its effect on the surfaces of the two respective objects.

this is poiselle's equation from fluid mechanic in physics. mech eng