# What makes a flying object keep moving with the Earth's rotation? [closed]

When a bird is flying or when a copter is hovering or a plane is flying what force is making them rotate with the earth beneath them?

• Why is this one on the astronomy site? Oct 11 '16 at 10:55
• A question related to the earth's rotation, you tell me where should i post it then sir? Oct 11 '16 at 18:26
• Hi, I guess just the physics site? physics.stackexchange.com Oct 11 '16 at 18:51
• @MuhammadUsmanQureshi In this case I agree with Joe, this is really not an astronomy question. Oct 12 '16 at 19:45
• @MuhammadUsmanQureshi Don't post it there until you read the question I linked and see if it answers yours. Otherwise it might get closed as a duplicate over there. Oct 12 '16 at 19:48

They aren't. To first order, airborne objects are moving with the Earth because they were moving when on the ground. However, what they retain is their angular speed, and since the circumference increases with altitude, an object that doesn't accelerate appropriately will appear from the ground to fall behind to the West (the Earth is rotating to the East). This is a well-known phenomenon whose magnitude is latitude-dependent, falling to zero at the poles.

• so if even I accelerate I will only be staying at the same spot on the ground as I go further up in the atmosphere? Oct 10 '16 at 13:57
• @MuhammadUsmanQureshi If you accelerate such that you match the angular speed of the earth's rotation then you'll remain over the launch spot. Oct 10 '16 at 14:29
• so if I have to go in the opposite direction that is east to west I just have to remain at o acceleration , since im not accelerating ill be going westward???? meaning im going at a constant speed towards east but I end up in a place west of my current position???????? that cant be true man Oct 10 '16 at 14:38

When something is flying through the air, it keeps moving along with the Earth because it was already moving that way to begin with. Remember that according to Newton's First Law, things will keep moving in the same direction unless an outside force acts on them. So when a bird, plane, or helicopter is on the ground, they are rotating along with the Earth. In the rotating reference frame of the Earth, they are stationary. From an external frame which sees the Earth as rotating, the object will be rotating in the same way. Now, when a plane takes off, it is changing its motion relative to the ground. In that reference frame, it begins moving. However, from our external reference frame, it was already moving. So its just changing its already non-zero velocity.

• That frame of reference thing i understand. But its not about take off, let me put it another way. Im in mid air in a helicopter and im just hovering 200m above the ground, going neither east nor west nor south nor north. Yet when i look down i cant see the earth rotate. Is it because gravity is pulling me with the rotation? Oct 9 '16 at 19:12
• @MuhammadUsmanQureshi no it's not gravity cause gravity doesn't pull you sideways. Your momentum is already moving in that direction and the Earth's atmosphere moves largely with the Earth's rotation so it would take a great deal of work (acceleration or deceleration as you prefer) to slow down to the point where you saw the Earth rotating below you and you'd have to fight a great deal of wind resistance. Everything is already moving with the Earth's rotation, so it takes a lot of energy and work to "stop" rotating with it. Oct 9 '16 at 20:05
• If my momentum is moving with earth's rotation then if i want to go in the other direction i will also need a lot of force to move even a single mile in that direction if im not mistaken? But that is not the case so why is that? Oct 10 '16 at 4:40
• @MuhammadUsmanQureshi The case of the ocean and the atmosphere is the same. The atmosphere is rotating along with the Earth, at the exact same rate. So if you are standing on the Earth, you are at rest relative to the air around you. Even if you jump off the ground or fly into the air, the air is still not moving relative to you. So it doesn't really help or hinder you, no matter which way you move. Oct 12 '16 at 17:22
• Think about it this way. Imagine you're on a train that's moving. Another train pulls up alongside you and matches your speed. You then step from your train across to the other train. When this happens, you don't feel any kind of force, and you don't have to fight against the train's motion, because you're moving at the same rate as it. It's the exact same principle. Oct 12 '16 at 17:29