Boxi Learn › Physics › Stage 3 · Structure and Evidence
Why doesn't a bed of nails hurt?
More nails means more points pushing into you, so it hurts more.
What presses in is pressure, force divided by area: the same weight spread over a thousand nails or a wide snowshoe presses a thousand times more gently than on one nail.
A friend says “a bed of nails must hurt more, because there are more points sticking into you”. Using the words “force”, “area” and “pressure”, explain why it is the other way round.
Hold a sharpened pencil between your two index fingers, point on one side and flat end on the other, and squeeze gently. Both fingers feel the same force — which one hurts? Then press your fingertip and then your flat palm into soft dough or wet sand with the same push and compare the dents.