How to understand aspects of science
Why don’t we fall through the floor?
They tell us that ‘action and reaction are equal and opposite’. But what does that mean?
It means that when we push against a wall, the wall pushes back. Here’s the clever bit. It pushes back with EXACTLY the same force as we exert on IT!
It means that when we stand on a floor, the floor pushes back. Again, it pushes back with EXACTLY the same force as our standing exerts on the floor. Otherwise, if the floor pushed with more, we’d fly into the air. If the floor pushed with less, we’d fall through the floor.
But how does the floor (and the wall etc.) know how to exert the exact force?
It knows because it deforms or bends. It might bend so little that you can’t see it, but it bends nevertheless. And as it bends, it is stressed. And the stresses build up till it bends all it can under YOUR weight. It then stops bending because there’s no more of your weight to resist. So the bending tells it how hard to push back! And it automatically knows how hard to push. That’s what happens, and it happens with every force/weight exerted, everywhere. Bridges, cranes, everything.
(In the ‘elastic’ region when bending is proportional to load, the structure returns to its normal shape when the load is removed. If loads are too high, then some deformation is permanent. )
Here’s something similar.
‘Floating bodies displace their own weight in water.’
What does that mean?
It means that when something floats, it knows how deep to sink into the water without sinking completely. How does it know?
It pushes water out of the way and THAT WATER is desperate to get back into its own space. But it can’t because the boat pushes back using its own weight. A compromise is reached. The weight of the water trying to get back is EXACTLY balanced by the weight of the boat keeping it out!! That’s what happens. With boats, rubber ducks and everything that floats.
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27 august 2016