Recently, I was in a car and noticed a plane in the sky. What was interesting was that the plane seemed to go slower than my car because I passed the plane. Is there a physics reason to this?
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2$\begingroup$ Key word "seemed". The illusion you saw was parallax. $\endgroup$– John AlexiouCommented Jan 17, 2015 at 2:33
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$\begingroup$ Of course, if it was a light aircraft you may have passed it with your car. A Piper J-3 Cub cruses at 65kt, which is 75mph. And that, of course, is airspeed, and there may be a headwind. $\endgroup$– Hot LicksCommented Jan 17, 2015 at 3:07
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$\begingroup$ Did you know that the plane was flying at a greater speed than your car? And was your car going in the same direction as the plane? $\endgroup$– Tea is lifeCommented Jan 17, 2015 at 5:33
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$\begingroup$ @scisyhp it seemed like a commerical plane... And yeah, it was pretty much going at the same direction as my car.. $\endgroup$– TanMathCommented Jan 17, 2015 at 6:40
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1$\begingroup$ Even though the motion seems slow as explained by one answer remember that if the observer moves a little bit it seems that wherever the observer goes the plane also goes with. If you go in the same direction and same speed as that of the plane the plane will always be with you above. You can never surpass it unless your speed is greater than that of the plane. $\endgroup$– Tea is lifeCommented Jan 17, 2015 at 7:31
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2 Answers
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There can be only two possibilities:
1. In case the plane and the car were moving in the same direction the plane was indeed flying with slower speed than the car.
2. In case the plane was flying with greater speed than the car the plane was going in some other direction. The component of velocity of the plane in the direction of motion of the car matters here which is lesser than the velocity of the car in your case.
Another way of seeing is (as the OP said the plane and the car were pretty much going in the same direction):
The car C can only see the background object B as coming out from the mouth of the plane P if the distance traveled by the plane PQ is smaller than the distance traveled by the car CD and the car will pass the plane also if B,P and C are always in straight line then the plane is traveling slower than the car and the car will pass the plane at the place where BPC is perpendicular to the ground. If the plane travels equal to or faster than the car then the car would see the background object B as coming out from the tail of the plane.
answered Jan 17, 2015 at 6:36
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Do you know about perspective? The more the distance, the smaller the objects look, and the slower the motion seems. For example, when you are on a rapidly-moving train and you look out of the window, you will just find that objects at the horizon seem to stand still, while the objects near the window flashes by at an amazing speed, and you will just feel like you are kind of revolving round a certain point at the horizon. However, actually all the objects, near or far-away, share the same speed at which they move away from you.
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$\begingroup$ That doesn't mean that an object at the horizon would seem to lag behind if the object at the horizon is moving with a speed greater than that of the train (which is generally the case that planes go faster than cars). $\endgroup$– zealCommented Jan 17, 2015 at 8:23
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$\begingroup$ The reason, however, is similar. Both are the effect of perspective.Suppose the plane moves at 300 m/s, and the car at 5 m/s, it is not strange that 300 m at the plane's distance looks even much shorter than 5 m at hand. $\endgroup$– VimCommented Jan 17, 2015 at 8:34
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$\begingroup$ I think you didn't read the question properly. The OP is saying that he passed the plane. I guess the OP very well knows that if we look at planes flying in the sky they seem to fly slowly. $\endgroup$– zealCommented Jan 17, 2015 at 8:40
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$\begingroup$ oh sorry... that I did look out this detail. and I just read that the OP said he was going in the same direction as the plane and he seemed to pass the plane. Then there could be only two cases: The plane was indeed slower than his car, or it was just some kind of illusion. and I think perhaps the latter is more acceptable LOL $\endgroup$– VimCommented Jan 17, 2015 at 8:51