Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 23/07/2007 21:18:09
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I am sure this must have been previously asked, but Why do we not feel the earth turn? Also, why if i went up in a helicopter and just hovered, would/does the ground below me not spin like a giant prize wheel?
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A couple of reasons - when you took off you were moving with the earth and objects tend to keep going in the direction they started moving in at a constant speed unless acted upon by a force. So if you are sitting on a spaceship moving at 100000mph and you let go, you will keep moving at 1000000mph close to the spaceship.
So there is a tendency to move at the same speed as the earth, and if you didn't you would be loads of air resistance/friction to accelerate you until you were.
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We can 'see' the effect of the earth turning by looking at shadows moving. It's just fast enough to see, with a bit of patience.
People had a great difficulty with this when the Earth was no longer thought to be at the centre of the universe and needed to be rotating. The fasted they had ever traveled was on a galloping horse and that could blow your hat off1
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The moving shadows don't show that the earth moves; they could quite easily be explained by saying the sun moves.
However Foucault's pendulum shows that the earth really does move.
http://en.wikipedia.org/wiki/Foucault_pendulum
The real reason that we don't feel the earth's spin is that the effects are small. With a really good spring balance you can show that the effect of gravity is slightly less at the equator than near the poles, part of that effect is due to the earth's spin (part is due to the fact that the earth isn't exactly spherical).
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I remember calculating the centrifugal force due to the Earth's spinning around. It amounts to 0.0035 g at the Equator, must be about half that much in the UK.
BTW, what would you see if you put Foucault's pendulum on the Equator, letting it swing among the meridian ? Should we ask Neil to go and test it ?
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We are told that the Foucault's pendulum aligns it's self to the fixed stars, it has always intrigued me as to whether this refers to the local galaxy or the universe as a whole.
This is of course difficult to measure due to the slow rotation of the milky way but theorists must have considered it.
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Paul...I thought i'd put this link here cos Ian (Soul Surfer ) also answered the same question http://www.thenakedscientists.com/forum/index.php?topic=3387.0
again...this is just a supplement to a rather spiffing question.
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Paul...I thought i'd put this link here cos Ian (Soul Surfer ) also answered the same question http://www.thenakedscientists.com/forum/index.php?topic=3387.0
again...this is just a supplement to a rather spiffing question.
Thank you, kind sir.