| Topic: |
Science > Physics |
| User: |
"Brablo" |
| Date: |
11 Sep 2006 04:12:05 PM |
| Object: |
Hovering projectiles... |
The amount of total energy for a bullet in flight is actually quite
little. An order of magnitude approximation should be about 5,000
Joules of energy for a bullet.
However, suppose that one were to design a hovering bullet which only
travels at 10 m/s. This bullet contains a very small camera and
guidance system, and it's operated remotely, let's say. Moreover, the
slow speed allows this 0.01 KG bullet to turn corners and explode on
the operator's wishes.
It seems to me, however, that it's far easier (and requires less
energy) for the bullet to go 1000 m/s for 10 second than it is for the
same bullet to go 10 m/s for 1000 seconds. But the amount of energy to
propel the bullet to 1000 m/s is a lot more according to the equation
KE = (1/2)*m*V^2
Why is it far more difficult to device a hovering bullet, which in
theory, takes up far less energy and force? On the other hand, the
conventional Mach 3 bullet takes up far more energy. My intuition
tells me that the slower bullet should take a *LOT* more energy than
the faster/conventional bullet, but this seems to contradict the
equations.
Why is this?
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| User: "Dr Moria" |
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| Title: Re: Hovering projectiles... |
11 Sep 2006 04:26:12 PM |
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"Brablo" <gestureofrespect@yahoo.com> wrote in message
news:1158009125.757957.70370@p79g2000cwp.googlegroups.com...
The amount of total energy for a bullet in flight is actually quite
little. An order of magnitude approximation should be about 5,000
Joules of energy for a bullet.
However, suppose that one were to design a hovering bullet which only
travels at 10 m/s. This bullet contains a very small camera and
guidance system, and it's operated remotely, let's say. Moreover, the
slow speed allows this 0.01 KG bullet to turn corners and explode on
the operator's wishes.
It seems to me, however, that it's far easier (and requires less
energy) for the bullet to go 1000 m/s for 10 second than it is for the
same bullet to go 10 m/s for 1000 seconds. But the amount of energy to
propel the bullet to 1000 m/s is a lot more according to the equation
KE = (1/2)*m*V^2
Why is it far more difficult to device a hovering bullet, which in
theory, takes up far less energy and force? On the other hand, the
conventional Mach 3 bullet takes up far more energy. My intuition
tells me that the slower bullet should take a *LOT* more energy than
the faster/conventional bullet, but this seems to contradict the
equations.
Why is this?
what is the difference between Energy and Work?
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| User: "PD" |
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| Title: Re: Hovering projectiles... |
12 Sep 2006 06:25:26 AM |
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Brablo wrote:
The amount of total energy for a bullet in flight is actually quite
little. An order of magnitude approximation should be about 5,000
Joules of energy for a bullet.
However, suppose that one were to design a hovering bullet which only
travels at 10 m/s. This bullet contains a very small camera and
guidance system, and it's operated remotely, let's say. Moreover, the
slow speed allows this 0.01 KG bullet to turn corners and explode on
the operator's wishes.
It seems to me, however, that it's far easier (and requires less
energy) for the bullet to go 1000 m/s for 10 second than it is for the
same bullet to go 10 m/s for 1000 seconds. But the amount of energy to
propel the bullet to 1000 m/s is a lot more according to the equation
KE = (1/2)*m*V^2
Why is it far more difficult to device a hovering bullet, which in
theory, takes up far less energy and force? On the other hand, the
conventional Mach 3 bullet takes up far more energy. My intuition
tells me that the slower bullet should take a *LOT* more energy than
the faster/conventional bullet, but this seems to contradict the
equations.
Why is this?
Here is the mistake: A bullet fired from shoulder-height horizontally,
will not be in the air for 10 seconds, let alone 1000 seconds. It will
fall, taking the same time as if it were simply dropped, about half a
second, no matter how fast it is going horizontally. It's a common
mistake to think that high horizontal motion somehow prevents vertical
motion. The two happen independently.
Furthermore, it's much easier to supply kinetic energy all at once to
the bullet while in the barrel of the gun, than it is to supply it
continuously to keep it hovering.
PD
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| User: "Brablo" |
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| Title: Re: Hovering projectiles... |
12 Sep 2006 08:53:51 AM |
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Hello PD
I totally understand the laws of kinematics (assuming a vacuum
exists),and I'm very adept at applying these equations.
However, from a theoretical point of view: For a bullet to travel
1000m in 1 second should take about the same amount of energy as a
bullet travelling 100 meters in 10 seconds. If anything, the latter
case requires *less* energy since there is far less drag.
Given that the "slow" bullet uses up much less energy, why is it
intuitively and practically very difficult - if not impossible - to
devise a very slow hovering bullet?
Can you calculate the amount of energy it would take to fire a bullet
at 1000 m/s VS a hovering bullet travelling at 10 m/s?
Furthermore, it's much easier to supply kinetic energy all at once to
the bullet while in the barrel of the gun, than it is to supply it
continuously to keep it hovering.
PD
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| User: "Randy Poe" |
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| Title: Re: Hovering projectiles... |
12 Sep 2006 09:24:47 AM |
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Brablo wrote:
Hello PD
I totally understand the laws of kinematics (assuming a vacuum
exists),and I'm very adept at applying these equations.
However, from a theoretical point of view: For a bullet to travel
1000m in 1 second should take about the same amount of energy as a
bullet travelling 100 meters in 10 seconds.
Why does it take any energy at all? What theory is behind
your "theoretical point of view"?
If anything, the latter
case requires *less* energy since there is far less drag.
Ignoring drag, if both are fired from a height of 1 m, they
will both reach the ground in 0.45 second. The first bullet
will have traveled 450 m in that 0.45 second, the second bullet
will have traveled 45 m in the same time.
So you don't have either a "bullet traveling 100 m in 10 seconds"
or a "bullet traveling 1000 m in 1 second". You have two
bullets that hit the ground in 0.45 second after traveling
different distances. No energy is expended in traveling those
distances.
If you fire from a height such that the bullets do have 10
seconds of potential travel time, then again they both
hit the ground at the same time (ignoring earth curvature)
and don't expend any energy in doing their traveling. In
fact they gain KE in the process of falling. Both gain the
same amount of KE.
why is it
intuitively and practically very difficult - if not impossible - to
devise a very slow hovering bullet?
Now you're asking something different which is I suspect
your real question.
You're asking why it takes energy to hover, and why it's
hard to design a hovering vehicle the size of a bullet.
Can you calculate the amount of energy it would take to fire a bullet
at 1000 m/s VS a hovering bullet travelling at 10 m/s?
The energy of hovering has very little to do with the horizontal
velocity, unless that velocity can be used to provide lift as in
an airplane. I don't think a bullet gets much lift. You could
put little wings on it (but then you wouldn't want to impart the
horizontal spin bullets usually get), and in that case the lift is
definitely
velocity dependent, and the 1000 m/sec bullet would have more
lift. The amount of lift depends on the wing design.
- Randy
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| User: "PD" |
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| Title: Re: Hovering projectiles... |
12 Sep 2006 10:55:26 AM |
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Brablo wrote:
Hello PD
I totally understand the laws of kinematics (assuming a vacuum
exists),and I'm very adept at applying these equations.
However, from a theoretical point of view: For a bullet to travel
1000m in 1 second should take about the same amount of energy as a
bullet travelling 100 meters in 10 seconds. If anything, the latter
case requires *less* energy since there is far less drag.
Given that the "slow" bullet uses up much less energy, why is it
intuitively and practically very difficult - if not impossible - to
devise a very slow hovering bullet?
Can you calculate the amount of energy it would take to fire a bullet
at 1000 m/s VS a hovering bullet travelling at 10 m/s?
Keep in mind that a bullet in horizontal motion does not *use up* its
kinetic energy in flight. Kinetic energy is not "fuel" that is consumed
by motion. If there is no horizontal force acting on the bullet once
the projectile is launched, it will have just as much kinetic energy at
the end of its flight as it does at the beginning of its flight. In
fact, because gravity is accelerating the bullet downward (and doing
work on it), the bullet in prinicple has *more* kinetic energy when it
lands than when it emerged from the gun. (I'm ignoring air resistance
here, but correcting for that later is easy once we get this
misconception hammered out.)
PD
Furthermore, it's much easier to supply kinetic energy all at once to
the bullet while in the barrel of the gun, than it is to supply it
continuously to keep it hovering.
PD
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| User: "Ben newsam" |
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| Title: Re: Hovering projectiles... |
12 Sep 2006 10:36:29 AM |
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On 12 Sep 2006 04:25:26 -0700, "PD" <TheDraperFamily@gmail.com> wrote:
Furthermore, it's much easier to supply kinetic energy all at once to
the bullet while in the barrel of the gun, than it is to supply it
continuously to keep it hovering.
Oh, I don't know... you could keep it hovering by slowing it right
down to 1 m/s, carry it yourself all the way to the person you want to
shoot, and shove it up his arse.
--
Posted via a free Usenet account from http://www.teranews.com
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| User: "Sam Wormley" |
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| Title: Re: Hovering projectiles... |
11 Sep 2006 11:01:44 PM |
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Brablo wrote:
The amount of total energy for a bullet in flight is actually quite
little. An order of magnitude approximation should be about 5,000
Joules of energy for a bullet.
However, suppose that one were to design a hovering bullet which only
travels at 10 m/s. This bullet contains a very small camera and
guidance system, and it's operated remotely, let's say. Moreover, the
slow speed allows this 0.01 KG bullet to turn corners and explode on
the operator's wishes.
It seems to me, however, that it's far easier (and requires less
energy) for the bullet to go 1000 m/s for 10 second than it is for the
same bullet to go 10 m/s for 1000 seconds. But the amount of energy to
propel the bullet to 1000 m/s is a lot more according to the equation
KE = (1/2)*m*V^2
Why is it far more difficult to device a hovering bullet, which in
theory, takes up far less energy and force? On the other hand, the
conventional Mach 3 bullet takes up far more energy. My intuition
tells me that the slower bullet should take a *LOT* more energy than
the faster/conventional bullet, but this seems to contradict the
equations.
Why is this?
Bullets fall to the ground just like anything else--now you come along
and want to counter the effects of gravity, which will involve a force
to counter that of gravity.
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