Physics Question
- Thread starter WolfLMM
- Start date
No argument there. However, if the velocity is not changing, how can you say the parachutist is accelerating at a rate of 9.81 m/s^2?
To add to the weirdness:
There is no such thing as "stopped". There is only relative velocity. Say you are floating in space with a golf ball in your hand. You release the ball. OPPSS! It is going away from you, so it's moving. Grab it again. Release. OPPSS! It's coming towards you, so it's moving. Grab it again, release, and voila it's stopped.
Or is it? Well to you it's not going away or getting closer.
But you were moving 1,000,000 mph away from Earth. And at the same time, your brother was moving 1,000,000 mph towards the Earth doing the same experiment. Both of you have a golf ball that is "stopped", but they are moving 2,000,000 mph relative to each other.
You never know what "stopped" is. Earth is moving at fantastic speed relative to other celestial bodies. Where is the "stop" point that everything references to? There isn't one. Everything is moving depending how you look at it. And everything can be "stopped" at the same time to another observer.
There is no such thing as "stopped". There is only relative velocity. Say you are floating in space with a golf ball in your hand. You release the ball. OPPSS! It is going away from you, so it's moving. Grab it again. Release. OPPSS! It's coming towards you, so it's moving. Grab it again, release, and voila it's stopped.
Or is it? Well to you it's not going away or getting closer.
But you were moving 1,000,000 mph away from Earth. And at the same time, your brother was moving 1,000,000 mph towards the Earth doing the same experiment. Both of you have a golf ball that is "stopped", but they are moving 2,000,000 mph relative to each other.
You never know what "stopped" is. Earth is moving at fantastic speed relative to other celestial bodies. Where is the "stop" point that everything references to? There isn't one. Everything is moving depending how you look at it. And everything can be "stopped" at the same time to another observer.
I already answered that one:
Yeah, fun stuff. It gets really confusing when you try to measure the speed of light when moving very fast. But... I'll leave that for another time
Excepting when a bullet in in freefall, under the influence of gravity, it usually ceases to accelerate after it leaves the barrel of the gun.
The force that accelerates the bullet is the pressure built up in the chamber, and within the barrel, caused by the combustion of the propellent charge (gunpowder, to use the vernacular - although it is not normally what is traditionally known as gunpowder, which is now regarded as black powder).
Exactly where the peak acceleration happens depends on the way the propellent burns, which depends on factors such as the grain size of the propellent (smaller grains burn faster, but you can also change the shape of the grains, so the they start by burning faster, and then get slower, or visa versa). Generally, the longer the barrel, the more distance you have in which to build up speed, so you will use slower burning propellent.
In general, you want to be as efficient as you can in the conversion of propellent energy to building up speed in the bullet; so you want to make sure that when the bullet leaves the barrel, there is as little excess pressure behind the bullet as possible (as that excess pressure may make for a loader bang, but is otherwise wasted energy). Since the acceleration of the bullet will be proportional to the pressure built up behind the bullet, it therefore follows that you wish to minimise the amount of acceleration that happens just as the bullet is about to leave the barrel (ofcourse, with short barrelled guns, you may not have too much choice in the matter, but if that is the case, then you are wasting a lot of energy).
The force that accelerates the bullet is the pressure built up in the chamber, and within the barrel, caused by the combustion of the propellent charge (gunpowder, to use the vernacular - although it is not normally what is traditionally known as gunpowder, which is now regarded as black powder).
Exactly where the peak acceleration happens depends on the way the propellent burns, which depends on factors such as the grain size of the propellent (smaller grains burn faster, but you can also change the shape of the grains, so the they start by burning faster, and then get slower, or visa versa). Generally, the longer the barrel, the more distance you have in which to build up speed, so you will use slower burning propellent.
In general, you want to be as efficient as you can in the conversion of propellent energy to building up speed in the bullet; so you want to make sure that when the bullet leaves the barrel, there is as little excess pressure behind the bullet as possible (as that excess pressure may make for a loader bang, but is otherwise wasted energy). Since the acceleration of the bullet will be proportional to the pressure built up behind the bullet, it therefore follows that you wish to minimise the amount of acceleration that happens just as the bullet is about to leave the barrel (ofcourse, with short barrelled guns, you may not have too much choice in the matter, but if that is the case, then you are wasting a lot of energy).
^^ Quite true, but I believe we were tackling the problem of the bullet AFTER it left the barrel. The acceleration of a bullet in a gun is an entirely different matter, and very much interesting on its own.
Agree to disagree. If velocity is constant, acceleration is zero. I guess in a simple problem like this, I find it easier to solve using kinematics.I already answered that one:
Yeah, fun stuff. It gets really confusing when you try to measure the speed of light when moving very fast. But... I'll leave that for another time
Like when your standing in a bus and the bus starts speeding up(velocity increase
), you don't think of yourself accelerating but the people outside the bus see you as accelerating. Its all depends on the the reference point.
I don't disagree with you. The acceleration IS zero. It just so happens there are two forces acting in opposite directions, that add to zero.
I agree with you 100%, the total acceleration is zero. I'm just over-thinking it a bit, because I can. :hug:
2 things, In this problem you cant ignore air resistance as the question says "A bullet is fired straight up into the air"
it also says it "stops Briefly" Based on how the question is worded is a false statement.
the bullet is under power, and will +accelerate, then gravity and resistance will cause a -acceleration.
X2
Another few to guess at,
we know the speed of light but whats the speed of dark ?
Is cold really a measurement in itself ?
we know the speed of light but whats the speed of dark ?
Is cold really a measurement in itself ?
I was going to post something about a looter in Watts when they see the cops are coming, but decided not to.
