Question of the Week

Is elevator travel across Earth possible?

Wed, 26th Mar 2014

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Question

Binesh from Harlow asked:

If earth is rotating why do we need to travel in an airplane? Can we not arrive our destination if we stay static on the sky and land when the earth spins and when we spot on our destination place during the spin?

Answer

The EarthHannah - So, using the Earth’s natural spin to help long distance travel across its surface? Engineer, Professor Hugh Hunt from Cambridge University.

Hugh - The air around the Earth is moving at the same speed as the Earth. How fast is the Earth moving due its rotation? Well, it’s moving at about 1,000 miles an hour which means that if we did sort of hover at rest above the spinning Earth, the wind speed we’d feel would be 1,000 miles an hour. And that would be impossible to deal with unless you had an aerodynamic object like an aircraft with engines to hold yourself against the wind and that's exactly what an aircraft is. Concorde for instance could fly the equator at about 1,000 miles an hour and could stay still essentially. It would hover above the Earth. The Earth would be spinning around underneath it and it would then land somewhere else. If there were no atmosphere, it doesn't solve the problem because we then don't have aerodynamic lift to hold the plane up. So, we have to go into orbit and going to orbit, well the speeds there are even bigger – 20,000 miles an hour and that requires a lot of fuel and a spacecraft.

Hannah - So you, the Earth and the atmosphere are constantly moving very fast as the Earth rotates. If you jump up and somehow managed to stop, you'd be faced with a whopping 1,000-mile per hour winds. Get out of the wind and up into orbit and the fuel you'd have to consume to get there would far exceed the fuel used by a plane which uses the wind currents to their advantage. Another point is that as Newton worked out, objects keep moving at the same velocity unless a force is applied. So, stopping from speed is just as tricky as starting to get to speed in the first place. So even on an airless world, elevator style travel across the Earth using its spin would still use up energy and wouldn't be that different to other modes of transport. 

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We answered this question on the show...

Hannah - So, using the Earth’s natural spin to helplong distance travel across its surface? Engineer, Professor Hugh Hunt from Cambridge University.

Hugh - The air around the Earth is moving at the same speed as the Earth. How fast is the Earth moving due its rotation? Well, it’s moving at about 1,000 miles an hour which means that if we did sort of hover at rest above the spinning Earth, the wind speed we’d feel would be 1,000 miles an hour. And that would be impossible to deal with unless you had an aerodynamic object like an aircraft with engines to hold yourself against the wind and that's exactly what an aircraft is. Concorde for instance could fly the equator at about 1,000 miles an hour and could stay still essentially. It would hover above the Earth. The Earth would be spinning around underneath it and it would then land somewhere else. If there were no atmosphere, it doesn't solve the problem because we then don't have aerodynamic lift to hold the plane up. So, we have to go into orbit and going to orbit, well the speeds there are even bigger – 20,000 miles an hour and that requires a lot of fuel and a spacecraft.

Hannah - So you, the Earth and the atmosphere are constantly moving very fast as the Earth rotates. If you jump up and somehow managed to stop, you'd be faced with a whopping 1,000-mile per hour winds. Get out of the wind and up into orbit and the fuel you'd have to consume to get there would far exceed the fuel used by a plane which uses the wind currents to their advantage. Another point is that as Newton worked out, objects keep moving at the same velocity unless a force is applied. So, stopping from speed is just as tricky as starting to get to speed in the first place. So even on an airless world, elevator style travel across the Earth using its spin would still use up energy and wouldn't be that different to other modes of transport.

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CliffordK, Fri, 28th Mar 2014

If you are talking about down on the surface of Earth, then one's frame rotates with the rotation of the Earth, and it is essentially impossible to move independently of the already moving frame without exerting energy.. 

Earth's rotation does have a couple of side-effects though.  The movement of the Earth with respect to the sun creates hot/cold areas which in turn cause high/low pressure areas and winds including the Jet Streams which already are utilized to increase the speed of jet travel and to save fuel.  Unfortunately, not eliminating the jets.  However, you might be able to pick up jet streams with lighter than air craft such as balloons and blimps.

Earth's rotation and core does create a magnetic field.  However, I believe it would be difficult to utilize it for power.

There is also the Coriolis Effect which does affect some of the winds.  However, I think it will also affect travel across the poles.  So say you wished to fly from Canada to Siberia across the North Pole.  I believe if you plot a direct course over the North Pole, you may in fact end up somewhere else (further west from your plotted target, I think).

Underground, if you dug a tunnel directly from the USA to China, or from Britain to Australia, then in theory, in a perfect vacuum, you could jump down one hole, accelerate towards  the center of the Earth, then decelerate back to the opposite surface.  Of course, the hot, molten, center of the Earth would be a problem.  One would also have to add a subtle curve to compensate for the coriolis effect.  Even a "cord" across part of the planet should experience similar gravity acceleration/deceleration.

In space, there have been many theories of a Space Elevator, although at this time it is unclear whether one can be built, or if the technical issues are resolved, will it be built?

The theory is that if one placed a large object in orbit at about 36,000 km (22,500 mi), then it would remain stationary with Earth (like many of our communication satellites).  Then drop a super-strong cable to Earth, then it would seem to just hang there.

If one put one's space elevator in a somewhat lower orbit, then it would move eastward (moving faster than Earth's rotation), but it may also loose a significant amount of energy due to wind resistance and loose altitude depending on the speed differential.  Place it above the geosynchronous orbit, and it would move westward, and slowly gain altitude, and also increase the speed differential between Earth and the satellite.

Anyway, for a fixed space elevator, one might be able to climb up partway, then glide back down to Earth, although the vertical climb would take some energy.  If the tail was moving...  one might be able to grab on for a while, then release.. CliffordK, Fri, 28th Mar 2014

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