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Question:
Is there gravity in the ocean, or is it just water pressure. Please explain in simple English we are only in seventh grade.



Replies:
Yes there is gravity in the ocean, same as the gravity on the surface of earth. It is not very clear to me as to why and where you want to invoke pressure. Please elaborate.

Jasjeet


What may be puzzling you is the effect of buoyancy, that is the fact that you do not fall in water. Is gravity gone? No, but it is being compensated for by the upwards force of the water on you. Why should the water do that? Imagine sitting in a tub of water. Before you get in, the water is (say) 12 inches deep. After you get in, you fill part of the tub, and the water level is *higher*, say 13 inches deep. All the water that used to be where your body now is has been lifted up and spread around on top of the rest of the water in an inch-thick layer. That extra layer is being pulled down by gravity, and it would just love to slide back down to the bottom of the hole in the water that you occupy and fill that hole back up. But it cannot, because to do so it would have to push you up and out of the hole. On the other hand, your body wants to sink further down, but it cannot, because it would have to push more water up out of the hole. The forces are balanced at a certain point, and you do not sink or pop up, but the forces are not zero.

christopher grayce



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