A floor seems to just be. How such a passive object can provide an upward force is indeed a puzzle.

Teaching Guidance 5-11 11-14

This misconception appears in two forms. The first holds that friction happens only when things move (slipping). This idea is...

Teaching Guidance 5-11 11-14

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...

Teaching Guidance 5-11 11-14