# Would I be able to see a ball passing next to me at 340m/s ?

1. May 23, 2015

### gen66

Imagine a football(soccer) ball passing next to you with a speed of 340 meters per second. Would you be able to see that? I would like to ignore realistic details as the ball burning or leaving trails etc. I'm just interested if I would be able to see the actual ball passing next to me at that speed? 340m/s is MACH 1 speed.
What about 40 miles per second (65km/s)? Would I see that ball with such speed? (40mph/s is a meteor speed).

Thank you guys! :)

Last edited: May 23, 2015
2. May 23, 2015

### A.T.

If you look along the path, 340m/s is not that fast and you would see it coming. At 65km/s, maybe a glowing ball in the dark, if you don't' blink in the wrong moment.

3. May 23, 2015

### gen66

But what if I just have a visual in the space limits of 10 meters width in from of me and I'm focused there, when the ball passes through those meters would I see it? (I don't want to see it coming from 1-2 km away, I want to see it exactly when it passes in front of me if I keep my eyes focused there ) , same valid for the 65km/s ?

4. May 23, 2015

### A.T.

Depends on the contrast the ball has with the background and on how attentive you are. This is more of a biology question, than a physics question.

5. May 23, 2015

### gen66

Ok, white ball on a dark background space the ball is going to pass like 1 meter away from me, in front of my eyes, I'm attentive as an average 30 year old person from Europe. Do you think it's possible to spot this ball with 65km/s moving speed? I think it's quite a physics question, because I think the speed is extremely high, so I'm just thinking if the object can is moving so fast may be your eyes can't even see that... But actually we can't see bullets can we? And bullets travel 1km/s , I"m asking for a ball with 65km/s hahahahaha, I just answered my own question. Of course we won't be able to see that, so the question is just valid for the 340m/s.

Last edited: May 23, 2015
6. May 23, 2015

### A.T.

With enough contrast, like tracer fire at night, we do.

7. May 23, 2015

### Tom_K

In a 10 meter field of view, the ball travelling at 340 m/s would take 29 milliseconds to pass by.

According to Wiki: Observers can recall one specific image in an unbroken series of different images, each of which lasts as little as 13 milliseconds.

So it may be just possible to spot the 340 m/s ball, but more than likely the persistence of vision will mask it and it will go by unseen, but certainly not unheard!

As for the 65 km/s no way you would see that!

8. May 23, 2015

### eifphysics

By the way, 340m/s is about the speed of sound in air. I think whether or not we can see the object depends on its speed as well as its apparent size . We have a good chance seeing a supersonic aircraft, but not a bullet.

9. May 23, 2015

### gen66

These types of answers I love, pretty concrete answer, thank you sir!

10. May 29, 2015

### BHS

We have a ping pong ball cannon which shoots the ball at just under the speed of sound. In a classroom setting you cannot see the ping pong ball between the time the cannon is fired and when the ball hits the wall several meters away. On the other hand, that speed is not that much different from the speed of a jet aircraft. You can easily see such a jet fly by.

11. May 29, 2015

### Staff: Mentor

What color are the balls and the wall? Have you tried shining a flashlight across its path?

12. May 29, 2015

### BHS

We have used white and orange ping pong balls. The walls are mostly various "academic cinder block off-whites," but in one case a darker gray and another a darkly stained wood door. We have not tried to shine a light across the ball's path. It would take less than a millisecond for the ball to cross the path of a typical flashlight. If the light were strong enough, and background dark enough, I am certain you could see it. After all, you can see a strobe light flash which is very short in duration. The question would be how much is enough?