A speeding bullet.
Moderators: Gromit, Paul, slparry
A speeding bullet.
While on a trip, I wondered about the velocity of a departing bullet from a moving vehicle. Does the bullet gain the forward speed of the vehicle if fired forward, thus making it faster than if fired from a stationary position? Similarly, does the bullet loose some speed if fired from the back of the vehicle in the opposite direction to travel? I believe there is some relative time/place issues, but I do not know enough to develop the maths. Does any of this really matter? No. But I have to keep the grey matter churning.
Oyster. 1999 R1100S. Almost original.
Corvus wrote:How about if the vehicle was travelling as fast as a bullet leaves the muzzle, would the bullet actually leave the muzzle?
I would guess the energy created to propel the bullet would always make it leave the barrel at the natural speed of the bullet. The bullet must then travel at a speed of the vehicle + the bullet speed as it leaves the barrel. The bullet has its own velocity, regardless of the motion of the discharge platform. Interestingly, if the vehicle (discharge platform) were travelling at some hyper speed, ie light speed +, would the bullet be able to move forward to escape the barrel as the barrel would be moving forward faster than the bullets own speed?
Oyster. 1999 R1100S. Almost original.
oyster wrote:Corvus wrote:How about if the vehicle was travelling as fast as a bullet leaves the muzzle, would the bullet actually leave the muzzle?
I would guess the energy created to propel the bullet would always make it leave the barrel at the natural speed of the bullet. The bullet must then travel at a speed of the vehicle + the bullet speed as it leaves the barrel. The bullet has its own velocity, regardless of the motion of the discharge platform. Interestingly, if the vehicle (discharge platform) were travelling at some hyper speed, ie light speed +, would the bullet be able to move forward to escape the barrel as the barrel would be moving forward faster than the bullets own speed?
I suppose two people could throw and catch a ball on a moving train no differently to how they could in a sports hall? So long as the train is moving at constant speed and is moving in a perfectly straight line. They're out of the air drag so that doesn't affect things. Motion is relative. Stood still, on the face of the earth, the bullet is already travelling at a fair lick even before the trigger is pulled, depending on your viewpoint, no?
Your hint at the speed of light is interesting. You said "light speed+". Isnt the speed of light effectively a cosmic speed limit? Nothing can exceed it. That puts an interesting slant on your bullet thought experiment. If we add the speed of the bullet to the speed at which we already travelling, which I think is what you said, then what happens at exactly the speed of light? We can't add the speed of the bullet to the speed of light, because the speed of light is the absolute limit.
The speed of light being an absolute is currently being challenged; the more we learn, the more there is to find out. So my phrase is a tease, I meant as fast as possible instead of light +.
The throw ball in a train moves in an apparent normal manner, it does travel a diagonal relative to its start point due to the forward motion of the train.
Still stuck thinking about the bullet moving with or against the direction of travel.
The throw ball in a train moves in an apparent normal manner, it does travel a diagonal relative to its start point due to the forward motion of the train.
Still stuck thinking about the bullet moving with or against the direction of travel.
Oyster. 1999 R1100S. Almost original.
oyster wrote:
A) the more we learn, the more there is to find out.
B) The throw ball in a train moves in an apparent normal manner, it does travel a diagonal relative to its start point due to the forward motion of the train.
C) Still stuck thinking about the bullet moving with or against the direction of travel.
A) I really believe in that.
B) the "diagonal" thing you mention, this surely is only relative to someone outside the train? Not moving with it, but looking on.
C) if you're in/on the vehicle in question, then no matter which way you fire won't the bullet leave you at the same speed? Except for "outside influences" which spoil the purity of the thought experiment. Like air drag!
Referenced from another galaxy, we are already on rapidly moving vehicle, just stood still on the face of the earth. So it doesn't matter to us if we fire the bullet in the same direction as which the earth is spinning, or the opposite. But it matters from an outside reference point, which is already seeing us moving though space.
I think!
But I'm open to persuasion!
As we're not dealing with the speed of light or any relativistic effects (therefore 11S's must be excluded from the discussion 
):
As appears to a bystander:
- velocity car: 100 kph.
- velocity of bullet being carried in car before it was fired: 100 kph (same as car).
- muzzle velocity of bullet fired from gun in car: 1000 kph. This is relative to the gun.
But the gun is already moving at 100 kph.
So the bystander would see the bullet, once fired, travelling at 100 + 1000 kph.
Bullet fired rearwards: speed 900 kph as seen by bystander.
If car could travel at 1000 kph and the gun fired rearwards, the bullet would have zero velocity as seen by the bystander, and would drop on the road in front of him. LOL. But only if the barrel was poking over the rear of the car.
Now, relative to an observer in the car, the bullet will always travel at 1000 kph, irrespective of direction.
):
As appears to a bystander:
- velocity car: 100 kph.
- velocity of bullet being carried in car before it was fired: 100 kph (same as car).
- muzzle velocity of bullet fired from gun in car: 1000 kph. This is relative to the gun.
But the gun is already moving at 100 kph.
So the bystander would see the bullet, once fired, travelling at 100 + 1000 kph.
Bullet fired rearwards: speed 900 kph as seen by bystander.
If car could travel at 1000 kph and the gun fired rearwards, the bullet would have zero velocity as seen by the bystander, and would drop on the road in front of him. LOL. But only if the barrel was poking over the rear of the car.
Now, relative to an observer in the car, the bullet will always travel at 1000 kph, irrespective of direction.
Real torque curves don't have a first derivative. :-^)
Re: A speeding bullet.
oyster wrote:While on a trip, I wondered about the velocity of a departing bullet from a moving vehicle. Does the bullet gain the forward speed of the vehicle if fired forward, thus making it faster than if fired from a stationary position? Similarly, does the bullet loose some speed if fired from the back of the vehicle in the opposite direction to travel? I believe there is some relative time/place issues, but I do not know enough to develop the maths. Does any of this really matter? No. But I have to keep the grey matter churning.
Not fast enough to worry about relativistic stuff.
As one approaches the speed of light, mass, time, length all change in the proportion of:
1/sqrt(1 - (Our speed)^2/(Light speed)^2)
Say Our speed = 1000 kph = approx 300 m/sec
Light speed = 300,000,000 m/sec
(Our speed / Light speed)^2 = (300/300,000,000)^2 = (1/1,000,000)^2
equals (1/1,000,000,000,000) = very very small.
The first line then becomes, for all intents and purposes: 1.
Meaning at our everyday speeds, nothing relativistic occurs
Keeps my grey matter churning too. Advice is to "do Sudoku". Corrrrr I'd die of boredom. One riding mate is 80, has an online specialty electronics business, and rides an R1200GS LC. Fast.
.
Real torque curves don't have a first derivative. :-^)
HerrFlick wrote:As we're not dealing with the speed of light or any relativistic effects (therefore 11S's must be excluded from the discussion
As appears to a bystander:
- velocity car: 100 kph.
- velocity of bullet being carried in car before it was fired: 100 kph (same as car).
- muzzle velocity of bullet fired from gun in car: 1000 kph. This is relative to the gun.
But the gun is already moving at 100 kph.
So the bystander would see the bullet, once fired, travelling at 100 + 1000 kph.
Bullet fired rearwards: speed 900 kph as seen by bystander.
If car could travel at 1000 kph and the gun fired rearwards, the bullet would have zero velocity as seen by the bystander, and would drop on the road in front of him. LOL. But only if the barrel was poking over the rear of the car.
Now, relative to an observer in the car, the bullet will always travel at 1000 kph, irrespective of direction.
That's exactly what I said!
I may need some time with your second post!
Re: A speeding bullet.
HerrFlick wrote:oyster wrote:While on a trip, I wondered about the velocity of a departing bullet from a moving vehicle. Does the bullet gain the forward speed of the vehicle if fired forward, thus making it faster than if fired from a stationary position? Similarly, does the bullet loose some speed if fired from the back of the vehicle in the opposite direction to travel? I believe there is some relative time/place issues, but I do not know enough to develop the maths. Does any of this really matter? No. But I have to keep the grey matter churning.
Not fast enough to worry about relativistic stuff.
As one approaches the speed of light, mass, time, length all change in the proportion of:
1/sqrt(1 - (Our speed)^2/(Light speed)^2)
Say Our speed = 1000 kph = approx 300 m/sec
Light speed = 300,000,000 m/sec
(Our speed / Light speed)^2 = (300/300,000,000)^2 = (1/1,000,000)^2
equals (1/1,000,000,000,000) = very very small.
The first line then becomes, for all intents and purposes: 1.
Meaning at our everyday speeds, nothing relativistic occurs
Keeps my grey matter churning too. Advice is to "do Sudoku". Corrrrr I'd die of boredom. One riding mate is 80, has an online specialty electronics business, and rides an R1200GS LC. Fast.
.
Ah, right. I see what you're sying. But what happens to the fired bullet, shooting it in a forwards direction, when we are going at the speed of light? Your number then equals zero.
(Edit. No it doesn't! It equals 1 !)
Or even at a speed just sufficiently below speed of light, but a speed at which adding the speed of the bullet takes the combined speed of the bullet to a higher value than the speed of light?
The clue, I reckon, is that the added together speed of bullet and travelling speed only applies (in apparent fashion) to a stationary observer.
mrjon wrote:If a cargo plane can carry the weight of 1000 pigeons, can it carry 2000 pigeons provided you keep 1000 of them flying around the cabin?
Can we simplify that? How about a box on a very sensitive weighing scale, with just one bird on a perch. We note the weight. The bird gets bored and starts flying around. What happens to the displayed weight?
Would it make a difference what kind of motion the bird made in the air?
mrjon wrote:If a cargo plane can carry the weight of 1000 pigeons, can it carry 2000 pigeons provided you keep 1000 of them flying around the cabin?
Ahh, now I did that one in a test! The mass (weight) of the birds is always in the truck. If the birds all took off within the truck, their downward force via the wings is still being supported by the truck. Result, truck's load is constant.
Oyster. 1999 R1100S. Almost original.
Corvus wrote:mrjon wrote:If a cargo plane can carry the weight of 1000 pigeons, can it carry 2000 pigeons provided you keep 1000 of them flying around the cabin?
Can we simplify that? How about a box on a very sensitive weighing scale, with just one bird on a perch. We note the weight. The bird gets bored and starts flying around. What happens to the displayed weight?
Would it make a difference what kind of motion the bird made in the air?
Years ago I posed that concept as a brain teaser to my children:
- you have to carry a brick and a bucket of water.
- since a brick weighs less in water than in air, why not suspend the brick in the water using a string attached to the handle of the bucket, so it would weigh less and so be easier to carry?
I think they're still arguing, even though one now has a PhD of Material Science from Imperial. LOL
Real torque curves don't have a first derivative. :-^)
Who is online
Users browsing this forum: No registered users and 23 guests