Why does the weight varies from place to place on the earth's surface?

Answer 1

Because people eat a lot when they travel on vacation.

Just kidding.

Because your "weight" is determined by gravity, and gravity varies very slightly over the face of the earth. Nothing you would notice in ordinary experience, but if you doing something like trying to target an intercontinental missile or steer a satellite (where slight miscalculations matter) it would make a difference

Think of weight as mass plus gravity. What is mass? If something is floating in space it has no weight but it still has its mass. A 200 pound steel anvil will weigh nothing in space but still have the same mass. It's a weird concept, don't fight it, mass is the stuff something is.

Your "weight" is your mass being attracted to the mass of the earth, like two magnets. The more mass you have (the bigger you are) the more gravity. This is why you one sixth on the moon, because the moon only has one sixth the mass of the earth.

One more concept: the closer two masses are to each other the stronger the gravitational attraction. So as you get away from the earth it's gravity becomes weaker and weaker until you are weightless in space. For a reference point they measure distance from the center of the earth (as in Journey to The Center of the Earth).

HERE IS YOUR ANSWER: The earth is not perfectly round, it is slightly egg-shaped, wider at the equator as it spins. The farther you are from the center of the earth the less gravity, the less you weigh. So if you are on a high mountain or at the equator you will weigh a teeny bit less. Your mass stays the same though.