Mailbox: Gold bars and gravity

23 September 2019

GOLD-BAR

Gold bar

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This week, Peter Bridger has been in touch about an interesting experiment involving gravity and a gold bar, and Rob Clements is closing to completing a truly iconic challenge...

Chris - We’re onto the mailbox now, this is the part of the program where we read out your correspondence. Now Peter Bridger has got in touch from Australia, and he sent us a very nice letter. It went actually all over the place, before it finally arrived to us. I'm sorry we're coming to this slightly late Peter, but he's been in touch telling us about the time that he spent here in Cambridge, because he was originally working with centrifuges, and this got him thinking and wondering about gravity, and so he's proposed an experiment and he says: Well could you take a gold bar all over the world and measure the gravity that it feels at the equator compared with the poles. And the rationale behind this idea is that because the equator is spinning a lot faster than the poles are, then the bar ought to weigh a bit less there apparently, because it's not being flung out into space at the poles in the same way as is at the equator. Adam is that a good idea?

Adam - I think it is. I mean the first thing to say is; we're not going to get flung off the planet like some horrifying roundabout, gravity is much much stronger than any spinning the Earth does. But it's a very good experiment because it's one that's been done a lot throughout history, and they've found but in different parts of the world gravity actually is different, and they found that it can waver by up to about 0.5% of how heavy something is. So in cities like Kuala Lumpur or Singapore which are by the equator, something is half a percent lighter than it is in places like Oslo because that's at the poles.

Chris - Pretty extreme way to go on a diet though isn't it? To go down to the equator just to lose a little bit of weight.

Adam - I mean if that's what you gotta do to make yourself feel better about scales that's what you got to do.

Chris - So it has been done?

Adam - It has. Yes. Not only have they gone to these places with weighing scales because that's how you measure how much something weighs we've had satellites in orbit measuring these things.

Chris - That's GRACE isn't it? The pair, or brace of satellites that actually whiz round the Earth and measure how fast one's accelerating relative to the other, because that's how they weighed the ice on Greenland to know what the rate of ice retreat was.

Adam - It's the Gravity Recovery And Climate Experiment is GRACE. And when one of them passes over somewhere heavy it gets pulled a bit ahead and then the other one catches up and that's how it measures things.

Chris - Thank you very much Adam. Meanwhile quick shout out to Rob Clements. Now he's in Nottinghamshire, and he's one of a very select band of brothers if I can put it like that because he's completed the audio equivalent of an ironman challenge, because he’s made it through our entire Naked Scientists podcast catalogue close to 1000 episodes going back to the very beginning. We’re one of the oldest and longest continuous running podcasts in existence so that's quite a feat. He has now reached August 2019, so Rob that red tape is in sight you're almost up to date, you're almost back in sync with the program. We're very intrigued to know if anyone else has managed a marathon like this, so if you're one of that band of brothers do let us know.

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