Why don't planes fly faster going west?
If the Earth is spinning towards the east at around 1,675 km/h (1,040 mph), it seems logical that an airplane would be able to fly to the west more quickly than to the east since it would be flying against Earth's rotation.
Why does this not happen?
It's because the plane is moving relative to the ground. Indeed, that's exactly what we're measuring. When the plane is on the ground it's moving at the same speed as the ground. When it takes off, the plane doesn't magically lose the speed it had on the ground and suddenly become independent of the Earth's speed. It keeps its initial speed and adds its own. The result is that the plane is going faster than Earth if its going east or slower than Earth if it's going west.
But the real point is that whatever speed the plane is going, it's travelling relative to the ground. It wouldn't matter how fast Earth is rotating, or if the Earth wasn't rotating at all. The only thing that matters is the difference in speed between the plane and Earth.
Here's an example... Imagine you're in an airplane on a smooth flight. You stand in the middle of the plane and throw a ball forwards at 10 m/s (33 ft/s). In one second it travels 10 metres (33 feet) forward. Now throw a ball backwards at the same speed. Does it travel slower or faster relative to the floor? Neither; it travels at exactly the same speed relative to the floor. In the same way, a plane taking off and travelling forwards (east) or backwards (west) will travel at the same speed relative to the floor (ground).
If you're concerned about the air in the atmosphere affecting the plane, there are two things two consider:
- Overall, Earth's atmosphere is moving at the same speed as Earth so it's all part of the same system with the same angular velocity. In the ball example above, the air inside the plane is moving at the same speed as the plane (except for local changes such as currents from air conditioning). Our atmosphere also moves at the same speed as Earth (except for local changes such as wind caused by different air temperatures). The atmosphere itself is not moving either east or west relative to the ground, there are only local winds.
- Wind does of course make a difference to planes. A plane flying into a headwind will clearly fly more slowly than with a tailwind.
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Author: Dave Owen