When two surfaces are in contact there is a force acting on each surface that acts in a direction to stop them moving past one...
A floor seems to just be. How such a passive object can provide an upward force is indeed a puzzle.
This misconception appears in two forms. The first holds that friction happens only when things move (slipping). This idea is...
For many learners air is seen as nothing. Comparing the mass of air in a small domestic room to the mass of a child might help...
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