HOW COME? Gravity differs on location

Surprise: It actually depends on where you're standing. In fact, the variations in Earth's gravitational field mean you'll weigh the teensiest fraction more in New York than you would in sunny Los Angeles.

Your weight is a measure of the Earth's downward pull on you. But gravity isn't something mysterious inside our planet. It's simply the attraction one bit of matter feels for another. When a snowflake falls to the ground, it's because the Earth is tugging on it. But the snowflake is also pulling -- just much more feebly -- on the Earth.

Gravity explains why matter tends to clump together -- into planets, stars, and the vast collections of stars known as galaxies. And we can thank gravity for keeping Earth endlessly circling the sun, rather than spinning off into the wilderness of space.

Gravity's strength depends on how much matter is packed into one space. The less-massive moon packs just one-sixth the gravitational pull of our planet. But while the gravitational pull of the Earth keeps the moon orbiting faithfully, the moon tugs, too, creating tides in Earth's oceans.

But even small clumps of matter are attracted. Imagine releasing two objects in space, far from the gravitational attraction of any planet or star. If a quart carton of milk and a 2-pound box of cereal were separated by about 3 feet in interstellar space, their mutual attraction would cause them to slowly drift together, with a gentle collision after about 12 hours.

Our planet's gravity causes falling objects to accelerate, at the rate of about 9.81 meters (32 feet) per second every second. If the Earth were a perfect sphere, its gravitational field wouldn't vary across its surface. However, because of its rapid spinning (about 1,000 mph at the equator), Earth actually bulges around the middle. Meanwhile, the moon's gravitational pull also subtly distorts our planet's shape, as does the varying topography of continents and oceans.

So objects at the equator are slightly more distant from the center of our planet's mass than objects at the poles, and experience a somewhat smaller gravitational acceleration. Gravity is likewise a bit weaker at the top of high mountains. (On Mount Everest, you would actually weigh about .28 percent less than at sea level).

The gravitational acceleration you experience in New York City is a bit stronger than in Los Angeles. In NYC a falling body will accelerate about a quarter-inch per second every second faster than in L.A.

See the rotating planet Earth's varying gravity at newsday.com/health.

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