Avi asked: The Earth turns around its axis at a speed of around 1,800km/h. A commercial flight flies at a speed of about half of this. If we fly to a destination located on the opposite side of the Earth and the direction of the flight is the same as that of the Earth’s rotation, we will not be able to reach our destination since the speed of the Earth is greater than that of the plane. If so, how do we still manage to reach our destination?


Hi Avi,

For hundreds of years humans believed that Earth was the center of the Solar System and that the moon, sun, planets and all the other stars revolved around it. This view was based upon the fact that the ground below us is stable and stationary, and when people looked up to the sky they saw the rest of the celestial objects moving and revolving around Earth. Nowadays, we know that this notion was incorrect. In order to understand the true nature of the Earth’s rotation along with the motion of a plane, we need to first understand what a ‘frame of reference’. 

When we wish to describe the motion of an object we first need to choose our frame of reference, namely a point to reference from where we want to measure (the coordinates of the origin), as well as the directions to which we are referring to in space (up,down or to the side). In addition, we need to choose the velocity of the system relative to another object (e.g., the ground). There are an infinite number of possibilities for choosing the frame of reference in any physics problem. However, the laws of physics will apply in all frames of reference, and no one is better than the other.

Let’s assume that a person is standing on a platform at the train station and a train passes by at a velocity of 200km/h in an easterly direction, and a bicycle rider passes by at a velocity of 10km/h in the same direction. One frame of reference is the person at rest, while the train is moving east at 200km/h and the bicycle is moving east at 10km/h. The second frame of reference is moving with the train. In this frame of reference the train is at rest, the person on the platform is moving west at 200km/h relative to it, and the bicycle is moving west at 190km/h. We could also define another frame of reference that is moving with the bicycle rider. In this frame of reference, the train is moving east at 190km/h and the person on the platform is moving west at 10km/h. Even though it seems the correct answer is that in which the person is at rest since this is the frame of reference of the ground, all three are equally good.

We can understand from this that in order to state that an object is moving at a certain velocity, we need to define in reference to what point in space it is moving or in what frame of reference it is moving. When stating velocities in a physics problem, it is important to pay attention to what the frame of reference is. In your question, you claimed that the velocity of the Earth’s rotation is 1,800km/h and that the velocity of the plane is half of this, but this is not true – since both velocities are being measured according to different frames of reference.

 


Plane. Speed is relative. | Photograph by: Oyoyoy, Wikipedia
 

The rotation time of the Earth is measured compared to the stars being fixed, i.e. stars which move very slowly in the sky, and therefore serve as a good reference point that almost does not move relative to Earth. In this frame of reference, we will observe the Earth rotating east at 1,800km/h at the Equator. This means the ground of the Earth and everything attached to it also rotates at this speed. From this point of view, the plane standing on the ground will also be moving east at 1,800km/h.

A plane ascending and flying east at 800km/h relative to the ground will appear, relative to the fixed stars, to be moving east at 2,600km; while a plane flying west at the same speed of 800km/h relative to the ground, will appear to the fixed stars to be moving east at 1,000km/h. In both cases the ground moves east at 1,800km/h. Therefore, the speed of the plane relative to the ground is 800km/h, and it is able to reach its destination.

Boomerang – question back at you
In the 19th century it was thought that there is one unique frame of reference termed “aether” in which light  travels at the familiar speed of 299,792,458 m/s, and that all other frames of reference move relative to it. What famous experiment was performed in order to disprove this claim, and what theory in physics developed following it?

 

Hagai Edri
Department of Physics of Complex Systems
Weizmann Institute of Science


Article translated from Hebrew by Elee Shimshoni, PhD student at the Weizmann Institute of Science.
A note to the readers
If you find the explanations unclear or have further questions, please drop us a line on the forum. We welcome your comments, suggestions and feedback.

 

10 comments

  • Josh Hill

    Michelson-Morley experiment

    Michelson-Morley experiment failed which bothered Einstein greatly which led to his eventually theory of relativity because he knew the Earth spun. Answer to boomerang question

  • Dejan

    An answer is simple

    An answer is a GRAVITY! The rotation of the Earth does not affect so much an aeroplane because of gravity. If there is no gravity every time you jump in the air you would move 300m per second in the direction of the west! Source http://explorecuriocity.org/Explore/ArticleId/3072/earth-vs-airplane-why...

  • TRUTH

    THEY CANT ANSWER THIS ITS ALL

    THEY CANT ANSWER THIS ITS ALL PSEUDO SCIENCE BS...IVE SEEN 5 DIFFERENT RIDICULOUS ANSWERS TO THIS QUESTION.IF THE EARTH WAS A GLOBE IT WOULD TAKE 5 MINUTES TO PROVE YET ITS ALWAYS MUMBO JUMBO OR A MATH EQUATION THAT A NORMAL PERSPN DOESNT GET

  • Josh Hill

    Have you seen NASA Reference

    Have you seen NASA Reference Publication 1207 from 1988 stating a flat, non rotating Earth? I've found dozens of these from the army when they perform tests. They ALWAYS assume a flat, non rotating non turbulent atmosphere Earth. And I guess that elliptical orbit we have around the sun that has to change speeds to make sure the year length doesn't change we don't feel that either going mach 80. This indoctrination is incredible!

  • Rich

    Thin Air

    Based on atmospheric pressure at 35,000 feet, you're flying through air that's about 1/4 as dense as it would be at 2,000 feet. If an airliner is clipping along at 650 mph air speed and the earth below it is moving in the opposite direction at 1,000 mph, the oncoming thin air it's encountering should be much less of a factor. The plane should still be going significantly faster. Why isn't it? My second concern is what's happening to the sound barrier up there because these airliners are right at the barrier. Is the sound barrier speed at that altitude based on when the plane is six miles from air and in thin air?
    I know three commercial pilots and have asked these same questions with no clear answers.

  • אנונימי

    what the fudge did the diaper

    what the fudge did the diaper head just regurgitate? did he / she / it even address the question at hand?

  • d taylor

    This is just balderdash, the

    This is just balderdash, the earth does not rotate

  • San Nas

    Although you have provided a

    Although you have provided a detailed explanation of frames as points of reference I think you have negated to mention why the plane when it becomes a separate entity from the earth as in flight, why it doesn't achieve either vast acceleration or vast deceleration in comparison to earth rotation. Obviously, we see that the atmosphere moves at the same speed as the planet, if this is the case and a aircraft being its own entity why does it not see a vast acceleration in relation to the wind assistance from the atmosphere. Or mass deceleration due to wind resistance as we are stating that the atmosphere is also moving at the same speed, obviously this is presuming the aircraft is moving in an east/west movement or west/east. Indeed should Earth stop spinning suddenly the atmosphere wouldn't stop instantly with it and basically scrub the surface clean. So if this is the case why does it not have an effect on the aircraft being a separate entity, or are we to consider that despite the plan sitting in the atmosphere which its own acceleration and deceleration abilities, it is in fact still attached to the earth in some cosmic force that isn't gravity, as gravity lacks a detailed explanation for this scenario. Additionally why when a plane is following a compass north/south does the plane still travel in a westerly direction to maintain its longitude in flight?

  • Dennis Mwangi Kinyua

    Velocity is referred to as

    Velocity is referred to as the rate of change of displacement. Displacement is a vector quantity meaning that both magnitude and direction has to be considered. In this case, reference points give a solitude explanation of a starting point of the object, from which the end point can be used to determine the object's displacement. Thus, you cannot consider the plane as a separate entity since this would mean that its overall velocity would be 0. Unless your definition of "a separate entity" means something else, we have to come to fact with the reason that without any point of reference, the object's overall velocity would be 0. And this applies to every single object. For example: if you think of objects in outer space, they cannot be considered as separate entities since they are still under influence by gravitational field strengths which are proportional to the gravitational constant and the mass of the objects and the radius of separation between them and the centre of earth for example. Without a relative frame of reference, which in this case would be the centre of the earth, the object's overall velocity becomes zero. And this is not true, since we know that the object needs a certain velocity in order for the centripetal force keeping it in motion to be sufficient. Hence, we see that we can never consider any object as a separate entity due to these reasons. Nice question though!

  • TRUTH

    GET REAL WITH ALL THAT BS....

    GET REAL WITH ALL THAT BS.....HOW DOES A ROCKET FLY IN THE VACUUM OF SPACE.....IT DOESNT ITS ALL A MONEY SCAM..TAKE A DRONE PUT A PIEVE OF CARDBOARD UNDER IT AND TAKE OFF ....ITS REACTION AND ACTION......IF U PULL THE BOARD OUT REAL QUICK THE DRONE FALLS TO THE GROUND (AIR MOLECULES DONT HAVE ENOUGH TIME TO COME TOGETHER....IN THE VACUUM OF SPACE THERES NOTHING TO REACT AGAINST ///NASA LIES ITS ALL BS