11 March

Couple of times I've tried to talk about gravity here with the example of people using stairs. It takes no more effort to go 'up' stairs than to go 'down' them. You'll use more energy going up, but no more effort in the sense of straining to 'lift' yourself. No lifting is needed to climb stairs, in fact you can't lift yourself - it's physically impossible. Anywhere you're on the ground, including on stairs, the net force on you is zero. The ground pushes up into you to exactly balance the Earth pulling you down. Engineers often look at this and say 'but your centre of gravity has to be lifted to go up a step'. The centre of gravity has to rise, yes, but you *are* your centre of gravity, *all* of you rises, at the same time. You can't lift yourself, just as you can't pick yourself up by pulling on your shoelaces. The delusion though causes people to strain going up stairs, and to 'drop' down stairs. Big loud thumps both ways. All completely unnecessary.