DaveH said:
Ok so 24 hours for a rotation (we call this a 'day'). Do you accept that the given diameter of the earth is 7917.5 miles or have a circumference of 24,873.6 miles at the equator?
All right. So linear speed is distance over time, someone standing on a spinning earth at the equator will travel 24,873.6 miles in 24 hours, so:
24,873.6/24 = 1,036.4mph
or rounding it for convenience the 1,000mph you keep parroting. You said earlier you didn't know where the figure comes from, that is how we work out the 1000mph. Happy with that calculation?
Now here is something I think is going to blow your mind. This is not quite the image I was looking for, but you can imagine a sphere as a load of discs of different sizes stacked on top of each other, a little bit like:
You can see in that image that the largest disc is in the middle and there are smaller ones to where we could imagine the poles to be if it were a globe planet. The smaller disc has a smaller circumference so someone standing on one of those would travel a smaller distance in 24 hours. Applying to the real world, Sunderland is at a latitude of 54.9 degrees so that gives a smaller distance travelled per day for Sunderland, which in turn means a lower speed. Someone at Sunderland travels at 598.2 mph [1] which is approaching half the speed of people at the equator, and pretty close to the speed of a commercial aircraft. We don't get pinned back in our seats when flying, except a little while accelerating up the runway. What about other people? People in Newcastle are slower than people in Sunderland.
If you go to Svalbard (I really want to go there), you are only at 78.9 degrees latitude. Your speed is then 200 mph. We are approaching fast train speed here. Once you approach the pole, your speed gets lower and lower. Certainly within the realms of what we would consider a speed we would not really expect to notice.
Now what would happen if there was a straight line of people north to south, hand in hand from the northern tip of Russia down into Malaysia? For each person, the person on one side would be going faster than them and the person on the other would be going slower. How can that be? Would the people in the north act as an anchor for the whole line to stop the people at 1000mph flying away? What then if they all jumped? You said someone jumping the earth would spin under them, so if they all jumped at the same time to the same height, then would the straight line land in a diagonal? What if they carried a rigid bar between them, would this shatter as soon as they jumped?
Clearly that whole concept is absurd. So what is going on here?
We have been using linear speed to measure angular velocity and it works differently. The angular velocity of the spin of the earth is very small. 360 degrees in 24 hours, 15 degrees per hour, 0.25 degrees per minute or 0.004 degrees per second.
Using the same method, you can also picture the hands on a large clock. The tip of the minute hand travels slower than the bit that joins the hub. Does that make any sense? No, of course not. Spin a solid ball and the inside rotates slower than the outside, so does it just pull itself apart? No.
Essentially linear speed is bollocks when it comes to a rotating body. The earth spins very slowly and saying whoa 1000mph is just a load of crap. And again, we feel forces acting on us, not speed. Speed is mass x acceleration and if your speed is constant, acceleration is zero so there is no force. Like what I said above, you feel a plane accelerate up the runway but when at cruising speed, despite being over 500 mph, you can walk about the plane without feeling a thing. Zero force.
[1] Rotation speed at latitude calculator at
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, including the formula. Yes I can prove this from first principals and agree with it, yes it can be tested on a sphere of any size, but I didn't feel the need to go into that.
Genius