Ask a physicist anything. (5)

[mzungu]

Correct answer. Unfortunately, I can't give you full credit. You took it upon yourself to set gravity to 10m/s*s rather than the universal 9.8. Fittingly, I'm awarding you 98/100.

Since you did not specify at what height or geographical position then I rounded up the number, so;

HELL YEAH!!!

​

 

[Gracchus]

How high must one jump (in a vacuum obviously) so that you stay in the air for 1 second?

Obviously, this is a trick question. If you are jumping in a vacuum you are not in the air at all!

 

[MattRose]

Given your average bullet (well I did paint a smiley face on it), if you fire a gun on level ground with the gun level, and you drop a bullet at the same time from the same height as the gun, which hits the ground first? Assume a flat earth no matter how much it irks you.

 

[TheReasoner]

Given your average bullet (well I did paint a smiley face on it), if you fire a gun on level ground with the gun level, and you drop a bullet at the same time from the same height as the gun, which hits the ground first? Assume a flat earth no matter how much it irks you.

They will land at the same time.

 

[chris4243]

Given your average bullet (well I did paint a smiley face on it), if you fire a gun on level ground with the gun level, and you drop a bullet at the same time from the same height as the gun, which hits the ground first? Assume a flat earth no matter how much it irks you.

It depends which way the wind is blowing , at least if the gun is rifled.

 

[TheReasoner]

It depends which way the wind is blowing , at least if the gun is rifled.

Well, if the wind only has horizontal components to it's motion it shouldn't. As we're close to the ground that's a fair assessment. (Better and better the closer you get to the ground, too.) Nor if it's vertical component is the same at all places where the two bullets exist during the experiment. If that's the case they will hit the ground at the same time. IF the wind is different so as to create a difference in the forces working vertically upon the two bullets then you'll get a different landing time, sure. Otherwise, if the conditions are the same they should hit at the same time.

 

[Hespera]

Hi max 15

Please write something about what the implications would be if the earth had much lower gravity during dinosaur days, in line with the idea that they would be too heavy to walk about today.

 

[chris4243]

Ah, but what do you get when you combine the bullet's spin with a wind blowing horizontal and perpendicular to the direction of motion? On one side, the wind and the local disturbance to the air are in the same direction, and on the other in opposite directions. This will change the trajectory just like with a curve ball, but because of the limitations on wind and the direction of rotation, the bullet will either go up or down.

 

[mzungu]

Ah, but what do you get when you combine the bullet's spin with a wind blowing horizontal and perpendicular to the direction of motion? On one side, the wind and the local disturbance to the air are in the same direction, and on the other in opposite directions. This will change the trajectory just like with a curve ball, but because of the limitations on wind and the direction of rotation, the bullet will either go up or down.

On a flat earth both bullets will hit the ground at the same time unless the flying bullet's aerodynamics keeps it in the air (highly unlikely if it is spinning since there will not be a pressure differential on any side).

On a Curved Earth the speed of the flying bullet will affect the drop if it is high enough. If it exceeds escape velocity then bye bye bullet.

 

[Assyrian]

My physics and maths are pretty rusty, but doesn't drag depend on square of the velocity? In a vacuum the downward component of the velocity would be the same for a bullet dropped or fired horizontally. But in air wouldn't the drag on the bullet that is fired be the combination of horizontal and vertical velocities squared? Wouldn't the vertical component of this drag be greater than drag of it just fell?

 

[MattRose]

Given your average bullet (well I did paint a smiley face on it), if you fire a gun on level ground with the gun level, and you drop a bullet at the same time from the same height as the gun, which hits the ground first? Assume a flat earth no matter how much it irks you.

I was looking for "they hit the ground at the same time", but most of these comments are intriguing. Maybe they wouldn't hit together due to a stong enough cross wind that would cause a climb or drop on one side of the spinning bullet. The problem is that all of the knowledge that I learned getting my BA in physics (not a misprint) was in vacuums and flat plains.

OK, here's another one. Fire a gun straight up in a real world situation. Does it take the same time to go up as come down?

 

[mzungu]

I was looking for "they hit the ground at the same time", but most of these comments are intriguing. Maybe they wouldn't hit together due to a stong enough cross wind that would cause a climb or drop on one side of the spinning bullet. The problem is that all of the knowledge that I learned getting my BA in physics (not a misprint) was in vacuums and flat plains.

OK, here's another one. Fire a gun straight up in a real world situation. Does it take the same time to go up as come down?

No! The bullet has an initial push going up thus countering gravity's pull, while going down it is affected only by gravity plus air friction.

 

[MattRose]

No! The bullet has an initial push going up thus countering gravity's pull, while going down it is affected only by gravity plus air friction.

So what about in a vacuum? Electrolux to be specific.

 

[mzungu]

So what about in a vacuum? Electrolux to be specific.

same thing minus the air friction. However with air; the bullet will reach terminal velocity when the force of friction is equal to the pull of gravity.

 

[Wiccan_Child]

Thanks for that 28.1.11 video Wiccan Child. A bit daunting due to implants but I got through it .

Alas I don't recall the video... but you're welcome!

You DO know he was joking?

I don't believe he was - I think he was referring to the fact that good science must be done divorced of personal bias. We must embrace failed results as well as successful results with equal zeal, because they're still results.

And if he was joking, then my signature contains a flash of humour

 

[Wiccan_Child]

I was looking for "they hit the ground at the same time", but most of these comments are intriguing. Maybe they wouldn't hit together due to a stong enough cross wind that would cause a climb or drop on one side of the spinning bullet. The problem is that all of the knowledge that I learned getting my BA in physics (not a misprint) was in vacuums and flat plains.

OK, here's another one. Fire a gun straight up in a real world situation. Does it take the same time to go up as come down?

No: the terminal velocity of a standard bullet is (roughly) an order of magnitude lower than its muzzle velocity (that is, its velocity as it leaves the gun's muzzle). Plus, bullets wander by up to a mile as they descend due to wind, so there's going to be significant tumbling which changes the bullet's aerodynamic properties further.

 

[selfinflikted]

Which is better: Diet Coke or Coke Zero?

Hint: COKE ZERO.

 

[Cabal]

Which is better: Diet Coke or Coke Zero?

Hint: COKE ZERO.

Ew.

 

[pgp_protector]

Which is better: Diet Coke or Coke Zero?

Hint: COKE ZERO.

Unsweetened Ice Tea.

 

[selfinflikted]

Unsweetened Ice Tea.

What is this unsweetened tea you speak of? I'm from the South.