h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

OK I know this sounds really stupid , but do things weigh more at the poles ?
The reasoning behind this thinking is ;
1. The poles are closer to the centre of the earth .
2. If you stood at the equator the centrifugal forces would make you lighter.
There I've said it ! Told you it was stupid .

I normally unsubscribe quickly to these questions, but this one intrigues me on many levels

1. Why would you want to know?
2, if things do 'weigh' more , would the effort of lifting them be compensated by one's position at the pole?
3 I never really got my head around mass and weight when I studied physics as a child


Please help -

Not stupid at all.

Yes, things weigh more at the poles. The difference is only about 1% as far as I remember. I could work it out, but I've drunk too much wine.

Lanzababy, how do you mean "compensated by one's position at the pole"?

oh KB I was just out with sisters and a or two - so do excuse the rambling nature of the following -


if you are standing at the pole and have to lift something, would it *feel* heavier than if you lifted the same weight at the equator, or would the force required be balanced out by your muscles being more powerful due to their increase in 'mass'. see I told you I don't really get my head around concepts like this.

Right I see what you meant.

Think of mass as "how much stuff there is" in something, and weight as "how hard the stuff presses down". So a kg of lentils is still 1kg on the moon, but it would feel a lot lighter - its weight is less, but its mass is the same.

The mass in your muscles - the amount of muscle - wouldn't change, so it wouldn't feel any easier to lift something.

thank you for taking the time to write that explanation for me KB - much appreciated. I think I have been wondering about this since seeing pictures of the space lab, with things floating about - and wondered whether the stuff actually felt light, or it was relative to how weightless the astronauts were.

Take a look here for a map of the s gravity - http://photojournal.jpl.nasa.gov/catalog/PIA04652

t.

OK ,thanks for the replies . Why did I want to know ? well I am the sort of person who ponders such things when I cant sleep .
The nasa gravity map seemed to show gravity hot and cold spots distributed all over the place . Now I am thinking maybe I would be heavier at the equator , as there would be more planet [ mass ] under my feet .

At the equator, it would feel easier to lift things than at the pole, because the weight of the object is less.

But as I said before, it is only a tiny difference, perhaps 1%.

That's why I was reluctant to say it would "feel" lighter when talking about mass and weight. It's such a small difference that you probably would not feel it.

I doubt it's just 1%....

has been to both poles during the last year and he is considerable heavier now than he was before ... can't have anything to do with the food aboard his icebraker and the lack of exercise... must be this gravity thing, mustn't it...?

or...

The reduction in gravity due to you spinning around quickly at the equator is 0.34%.

I'm not sure of this next calculation, but I reckon the reduction in gravity due to being further from the centre of the earth is 0.67%. The two add up to 1.0%.

(The reason I'm not sure about that is that all the textbooks talk about the gravitational pull of a sphere. If the earth is an ellipsoid, can you calculate gravity using the normal formula of mass of radius squared?)

Pfft, tough one there at the end Gnomon. Probably not although the answer is unlikely to be massively different given the only slight ellipsoidness of the earth.


1% difference would be enough to make the difference in strong-man competitions . Maybe they should move the world's strongest man competitions to break records.

Of course that would only work once.

Blimey It appears I was thinking along the right lines . Not bad for somebody who's only science knowledge comes from TV and books/internet .