Why is the Earth Round and still has water ?
Answers
Answer:
If you see a globe on your table”
The details sentence is missing something, so I’ll answer this question:
If you see a globe on your table, and you put water on it, the water will run across the globe and then leave the globe and hit the ground. On Earth, how is the ocean water still staying on Earth rather than slipping into the space?
With the globe, if you put your finger on any point on the globe, you can find a tangent plane to the surface of the globe at that point. If you haven’t learned tangent planes yet, think of a sheet of paper that is stiff and hold it to the globe with one finger pressing the sheet of paper to the globe. That sheet of paper is the tangent plane.
Now, you can imagine a gravity vector that points in the direction of the force of gravity from that point. If your kitchen is like mine, the gravity vectors at every point are directed towards the floor. When you let something go in a gravitational field and it is not blocked by other things, it will start to move in the direction of the gravity vector. Depending on where your point is on the globe, the gravity vector might be pointing to the inside of the globe. For a waterproof globe, the water isn’t going in that direction. However if you project the gravity vector onto the tangent plane, you can have a vector that is on the tangent plane and points to where the water would go.
If this is a typical globe and your finger is on the Southern tip of Africa, the gravity vector is straight from that point to the ground. Put water there and it will fall to the floor. If your finger is on Norway, the gravity vector is into the globe, but the projection of the gravity vector is on the tangent plane and points in the direction of Denmark. So, when you put water on your globe at Norway, it heads to Denmark, then Germany, etc. and when it gets to somewhere lower (depending on your globe’s construction and orientation, the water falls to the floor.
OK, now do the same thing for the Earth. Standing somewhere on Earth, you imagine a tangent plane - or for the Earth, since it is almost flat, just imagine a few meters of flat all around you. The gravity vector everywhere on Earth (aside from some very small wiggles) points to the center of the Earth. As you know from geometry, a vector from a point on the surface of a sphere to the center of the sphere is perpendicular to a tangent plane on the surface of the sphere. So, no matter where you are on Earth, the gravity vector is pointing straight into the globe and since the projection of a perpendicular vector onto a tangent plane is zero, there is no tangential gravitational force on the water. It only goes down!
I guess the key difference is that for the Earth, the gravity vector is towards the center everywhere, whereas for a globe in your kitchen the gravity vector is towards the floor.