How come I can see a jet plane miles away but I can’t see a bullet going past me? And the plane doesn’t even have to be going that fast. Take 500 mph; it equals about 730 feet per second. I know I can’t see bullets going that fast. Why not?
Key factors seem to be the size of an object and how close it is to me. The bigger and/or farther away an object is, the easier it is to see.
I have two theories. One is that light, being partly a wave, is vulnerable to the Doppler Effect just like sound. Therefore, when a high-speed object is very close to me, some of its light is “scrunched” into wavelengths that I am not physically capable of perceiving. My other theory is that an object close to me going really fast is sending a continuous image to my brain that it cannot interpret at the same speed.
Umm… how bout the same reason you can see trees in a paddock when you are travelling in a car but not the grass on the side of the road. Even though they are both going at the same speed relative to you, the trees have a slower apparent motion because they are further away.
the “speed” your eyes can see is in radians/sec not meters per second.
Degrees/sec for us non-metricised freaks, but I agree with Shalmanese. A jet is very large and moves very slowly through your field of view, whereas a bullet wouldn’t be visible at the distance you’d see it moving from.
It is possible to see a slower bullet or BB if you’re the one shooting it and it’s in front of a contrasting background, because it won’t have much movement from your perspective.
Also, if a jet fighter buzzed your head at mach two, you probably wouldn’t see it coming and you definately wouldn’t see it going.
A 231 foot long 747 flying at 500 mph, moves from nose to tail relative to a stationary point in about 1/3 of a second, plenty of time for it to register on your retina retina. An inch long bullet moving at 500 mph, moves from nose to tail in 1/8760 of a second, far to short of a time for it to register with your eye.
I’m sure that if you fired a bullet that was 231 feet long, you’d be able to see it. Size does matter. It’s hard to pick out a gnat moving 3 feet away from you at 10 miles an hour while you have no problem picking out a car going at the same speed.
Light is subject to the Doppler effect, but the velocities have to be much higher for the effect to be noticeable. In astronomy, “red shift” means that the spectrum of a body (usually a galaxy or quasar) appears to us on Earth to be shifted in the red direction, meaning that the photons are lower energy than normal, meaning that the body is moving away from us at a fair percentage of lightspeed. Conversely, blue shift indicates the body is moving towards us. Since lightspeed © is 186,282 miles per second, the speeds of the bullet and plane figure to about 7 * 10[sup]-7[/sup] * c. Not exactly a fair percentage.
I think this is correct. The rate of movement in units measured in the length of the object moving is the key. A bullet moves many times its own length in a given period. I think this also explains why a 747 on the landing approach appears to be moving relatively slowly while a fighter plane whizzes along.
On rare occasions, when visibility was just right, I have seen bullets that I fired from my .270 rifle. And they are going about 2200 ft/sec muzzle velocity.
Likewise, under some limited circumstances, it’s possible to see artillery & mortar shells in flight.
If you ever want to see an apparantly slow moving aircraft, watch a C-5 or C-17 lining-up for a landing…
You can also, indeed, “see” bullets: If you watch films of tracer rounds being fired, you can see the slight phosphor trail that they leave as the tracing element burns off. The bullet (or its phosphor tail) is not 231 feet long, but it is quite adequately long to register on one’s retina so that you can see the motion of the round that is only .3 or .5 of an inch in diameter.