# Where On Earth Do You Weigh The Least?

published on July 20, 2020

Thanks to curiosity stream for supporting PBS Digital Studios hey smart people Joe here what weighs more a pound of feathers or a pound of steel sorry I forgot to switch the video into metric much better so what weighs more a kilogram of

Feathers or a kilogram of steel you're too smart you're right that's a trick question it all depends on where on earth you weigh them something's mass the kilogram of feathers a kilogram of steel where you and me is constant

Everywhere in the universe because mass is a measure of how much stuff there is all your atoms added together but weight isn't a constant it's the force of gravity applies to all that stuff at one specific spot so depending on the

Gravity where you are your weight will be different this makes sense if we think about being say on the moon where your moon weight is about 16 and 1/2 percent your earth weight because gravity is about 16 and a half percent

What it is on earth but the same thing is also true here things don't weigh the same everywhere on earth so a question where on earth would you or feathers or steel weigh the most and for that matter where would you weigh the least

What makes this question so confusing is there's more than one definition of weight up to most of us weights just the number you see when you step on the scale a scale does measure weight the force gravity puts on a mass but the

Numbers on the scale in kilograms or pounds are not measures of weights officially those are measures of mass and like we just saw mass and weight are different things so unless your bathroom scale gives you an answer in Newtons

It's lying to you now mass is the amount of stuff there is in you and weight is how hard gravity is pulling on you and all your atoms most that time this difference doesn't matter because if you weigh two things in the same place on

The same scale they're both under the same influence of gravity but a kilogram of feathers on the North Pole weighs more than a kilogram of steel on the equator the reasons why are pretty weird all of

This would be easy to figure out the earth were a perfectly smooth non rotating sphere floating alone in space nice and uniform all the way through on a planet like that gravity would be the same everywhere on its surface but we

Don't live on that spherical planet hey hey are you about to make a flat earth joke down in the comments I'm here to tell you to just say no to Flat Earth kids the only buzz I get it's for real science in the space we do this first

Problem is the earth is spinning well actually that's not a problem it's kind of a good thing it keeps half the planet from freezing solid but it also means earth isn't spherical earth's equator is spinning around at hundreds of meters

Per second and when a round object spins it bulges perpendicular to the axis of rotation the physics of why this happens it's not exactly simple but it's something you probably intuitively understand earth is actually ever so

Slightly squished and fatter near the equator plus someone's standing at the equator feels an apparent force pushing them away from the center of the earth just like one of those spinning carnival runs gravity gets weaker with distance

So being a bit farther from the center of the earth Plus that small centrifugal pole makes gravity at the equator about drum roll please Oh point five percent weaker than at the poles but this bulgy ellipsoid earth

Isn't the whole story either you see earth isn't like a smooth chocolate cake it's more like a brownie with nuts our planet has lumps and chunks with different densities that make gravity at the surface a little different all over

For example the crust beneath Iceland and the mid-atlantic ridge is more dense than in the Indian Ocean which means more mass which means stronger gravity in the North Atlantic when you take into account the actual distribution of

Matter in the earth gravity where you are maybe higher or lower depending on the kind of rock and the crust beneath your feet or if you're over water even once in the mantle below there's a lot to take into account so the real earth

Is a squished spinning lumpy irregular blob with uneven gravity but we need precision measurements of these gravity differences to keep super sensitive technology like GPS working right now we could go around and weigh something on a

Scale everywhere but that's a lot of work scientists have a way cooler method one NASA mission uses two identical satellites following each other on the same orbits as the first satellite passes over a spot with higher gravity

Its orbit speeds up and the two satellites pull apart when the second satellite passes over that high gravity spot it also speeds up and closes the distance but if the leading satellite passes over a spot with low gravity it

Slows down and the second satellite catches up a bit before passing over the slow spot itself this sounds like a never ending game of cat and mouse NASA agrees they even named the satellites Tom and Jerry scientists are

Able to measure the distance between these satellites to the width of a human hair in order to reconstruct a gravity map of our entire planet we've mapped differences as small as point zero zero

One percent in Earth's gravity these maps show how places like the Himalayas Andes Indonesia all have slightly stronger gravity while areas like the Hudson Bay or the Indian Ocean have slightly weaker gravity so let's go back

To our question from the beginning putting all of this together where on earth would you or a kilogram of feathers or steel weigh the most at a spot in the ocean near northern Russia the effect of Earth's rotation making

Gravity strongest near the North Pole combined with some especially dense crust puts point heavy right there and where on earth anyway the if you guess the equator you're close

Its wesker on a peruvian mountain that's just south of Earth's middle higher altitude combined with the Bulge creates the weakest gravity anywhere on the planet but the effect is pretty small if you drop the ball on top of the peruvian

Mountain it would only hit the ground 16 milliseconds later than it would at pointe heavy and if you took the same bathroom scale to both places a 70 kilogram person would only see about a half kilogram difference even though

Kilograms aren't a measure of leyte like we already talked about if you're looking to shed some weight thanks to a technicality of physics I mean it certainly wouldn't hurt to try scaling a mountain at least you'd burn some

Calories on your way up stay curious a big thank you to curiosity stream for supporting PBS Digital Studios what is curiosity stream it is a subscription streaming service that offers documentaries and nonfiction

Titles from a variety of filmmakers and their collection features a bunch of curiosity stream originals if you enjoyed this massively cool trip you should check out this original series from curiosity stream where the late

Great astrophysicist Stephen Hawking it takes you on a tour of his favorite places in the universe and explains how they got the way they are it's heavy in a whole different way you can learn more at curiosity Stream comm slash smart

You

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