When do we call a body rigid?

When do we say that work is done?

What do we call the gravitational force between the earth and an object?

When do we say two vectors are orthogonal?

Why do we apply paint on iron articles?

When will a moving body be in equilibrium?

Why do not we draw a boundary surface diagam within which the probability of finding the electrons is 100%?

Why do we use ball-bearings?

Why are solids rigid?