I read in 快猫短视频 that the pressure at Earth鈥檚 core is 3.6 million atmospheres. I would expect the pressure there to be zero, because it arises from gravity, and this must be zero at the core since the pull of the surrounding matter is equal in all directions. Can someone get to the bottom of this?
鈥� Don鈥檛 confuse the pressure at any point with the gravity at that point. Certainly the gravitational forces at the centre of mass cancel out, reducing weight to zero. But the gravity at every other point inside Earth is directed towards the centre of mass, increasing the pressure at all deeper points.
Imagine a tightly inflated elastic balloon: the gas at the centre is under high pressure, even though that pressure is applied only around the outside.
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Jon Richfield Somerset West, South Africa
鈥� The pressure at the bottom of the Mariana trench in the Pacific Ocean is more than 1000 atmospheres. If we were able to find a trench elsewhere that was twice as deep, the pressure there would be more than double that.
Keep going down further, and the pressure keeps going up. At the very centre of the Earth, the pressure is caused by the weight of about 6400 kilometres of liquid iron and rock lying above.
Just because gravity is zero at Earth鈥檚 centre doesn鈥檛 mean that the stuff overhead has suddenly become weightless. Imagine the heavy column of molten rock below Singapore that bears down on the core. On the other side of the globe, the weight of the molten column under Ecuador pushes down in the opposite direction.
An object at the centre of Earth鈥檚 core may be weightless, but it is like an orange pip being squeezed between your fingers.
Hugh Hunt Cambridge, UK
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This article appeared in print under the headline 鈥淯nder pressure鈥�