Science > Physics > newbie question on kinetic or vibrational energy (force)
| Topic: |
Science > Physics |
| User: |
"Vasileios Zografos" |
| Date: |
10 Mar 2005 05:57:12 PM |
| Object: |
newbie question on kinetic or vibrational energy (force) |
Hi, first of all let me say that I am no physicist, and my knowledge of
physics stops at high-school. My scientific field is quite different
(computer vision).
Now, this of the following example. I have a little glass box, and inside I
have a metal sphere. I shake this box and this sphere "jumps" around inside
the box. Imagine if you will, these popular games, where you have to shake
the box and make the ball (sometimes many balls) jump into a hole.
I have a question regarding the forces (or energies if you like) that are
exerted on the ball as we shake the box. Of course we have the gravitational
force (they call it potential force?) and some kind of vibrational force,
that we exert to the box and the box in turn exerts to the sphere. I assume
that this force become the ball's kinetic energy.
What I am looking for is a really basic formulation (I can deal with
derivatives and partial pdfs) for that vibrational force.
Can somebody help me please?
I know that the kinetic energy Ek=1/2mv^2 and that the potential energy that
the ball has is Ep=mgh...but what about that vibration?
Thank you in advance,
V.Z.
.
|
|
| User: "Vasileios Zografos" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
10 Mar 2005 06:05:35 PM |
|
|
Also I would like to point out that:
If this vibrational force is difficult to describe then I could settle for
the following.
Suggest an energy that you add (by add I mean you are God or wave a magic
wand and you add energy to the system ) to a stationery mass (i.e. a ball
resting inside a hole) that will make it jump out of the hole. I thought of
some kind of vibration...but what other choices are there? I originally
considered kinetic energy but I dont think it will cause the ball to jump
out.
I do apologise if all this sounds childish. This is not really my field.
:)
Thanks
"Vasileios Zografos" <vasileios@zografos.org> wrote in message
news:d0qmsp$eb3$1@newsg2.svr.pol.co.uk...
Hi, first of all let me say that I am no physicist, and my knowledge of
physics stops at high-school. My scientific field is quite different
(computer vision).
Now, this of the following example. I have a little glass box, and inside
I have a metal sphere. I shake this box and this sphere "jumps" around
inside the box. Imagine if you will, these popular games, where you have
to shake the box and make the ball (sometimes many balls) jump into a
hole.
I have a question regarding the forces (or energies if you like) that are
exerted on the ball as we shake the box. Of course we have the
gravitational force (they call it potential force?) and some kind of
vibrational force, that we exert to the box and the box in turn exerts to
the sphere. I assume that this force become the ball's kinetic energy.
What I am looking for is a really basic formulation (I can deal with
derivatives and partial pdfs) for that vibrational force.
Can somebody help me please?
I know that the kinetic energy Ek=1/2mv^2 and that the potential energy
that the ball has is Ep=mgh...but what about that vibration?
Thank you in advance,
V.Z.
.
|
|
|
| User: "Bjoern Feuerbacher" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
11 Mar 2005 03:52:29 AM |
|
|
Vasileios Zografos wrote:
Also I would like to point out that:
If this vibrational force is difficult to describe then I could settle for
the following.
Suggest an energy that you add (by add I mean you are God or wave a magic
wand and you add energy to the system ) to a stationery mass (i.e. a ball
resting inside a hole) that will make it jump out of the hole.
You will also have to add momentum in order for this to work.
I thought of some kind of vibration...
I don't see how one could accomplish this with "some kind of vibration".
but what other choices are there? I originally
considered kinetic energy but I dont think it will cause the ball to jump
out.
If the ball has kinetic energy *and momentum going outwards*, it will
jump out.
[snip]
Bye,
Bjoern
.
|
|
|
|
|
| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
10 Mar 2005 06:09:35 PM |
|
|
Dear Vasileios Zografos:
"Vasileios Zografos" <vasileios@zografos.org> wrote in message
news:d0qmsp$eb3$1@newsg2.svr.pol.co.uk...
Hi, first of all let me say that I am no physicist, and my
knowledge of physics stops at high-school. My scientific field
is quite different (computer vision).
Now, this of the following example. I have a little glass box,
and inside I have a metal sphere. I shake this box and this
sphere "jumps" around inside the box. Imagine if you will,
these popular games, where you have to shake the box and make
the ball (sometimes many balls) jump into a hole.
I have a question regarding the forces (or energies if you
like) that are exerted on the ball as we shake the box. Of
course we have the gravitational force (they call it potential
force?) and some kind of vibrational force, that we exert to
the box and the box in turn exerts to the sphere. I assume that
this force become the ball's kinetic energy.
What I am looking for is a really basic formulation (I can deal
with derivatives and partial pdfs) for that vibrational force.
Can somebody help me please?
I know that the kinetic energy Ek=1/2mv^2 and that the
potential energy that the ball has is Ep=mgh...but what about
that vibration?
You will have a forcing function on the box, that initiates the
"vibration". Simulate that however you need to. The ball can
probably be modelled as rigid, without internal vibration.
Unless the box is large, or the forcing function slow or low
amplitude, you can neglect "mgh". As the ball encounters a wall,
it will "reflect". It will also have momentum based on the
"coefficient of restitution" (which describes the wall-ball
interaction). Use conservation of momentum to get the rest.
David A. Smith
.
|
|
|
| User: "Vasileios Zografos" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
10 Mar 2005 06:33:34 PM |
|
|
Hi, and thank you for your prompt reply,
I am mostly interested in this forcing function rather than the momentum or
the reflecting force from the box boundary. (Imagine that the box is
inifinetly large so is doesn't actually come in touch with the boundaries).
Would it be possible for you to give me a basic formulation of this forcing
function?
Thank you,
V.Z.
"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com> wrote in
message news:Hk5Yd.4035$uk7.2717@fed1read01...
Dear Vasileios Zografos:
You will have a forcing function on the box, that initiates the
"vibration". Simulate that however you need to. The ball can probably be
modelled as rigid, without internal vibration. Unless the box is large, or
the forcing function slow or low amplitude, you can neglect "mgh". As the
ball encounters a wall, it will "reflect". It will also have momentum
based on the "coefficient of restitution" (which describes the wall-ball
interaction). Use conservation of momentum to get the rest.
David A. Smith
.
|
|
|
| User: "N:dlzc D:aol T:com \dlzc\ N: dlzc1 D:cox" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
10 Mar 2005 07:44:07 PM |
|
|
Dear Vasileios Zografos:
"Vasileios Zografos" <vasileios@zografos.org> wrote in message
news:d0qp13$6o4$1@news8.svr.pol.co.uk...
"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com>
wrote in message news:Hk5Yd.4035$uk7.2717@fed1read01...
Dear Vasileios Zografos:
You will have a forcing function on the box, that initiates
the "vibration". Simulate that however you need to. The ball
can probably be modelled as rigid, without internal vibration.
Unless the box is large, or the forcing function slow or low
amplitude, you can neglect "mgh". As the ball encounters a
wall, it will "reflect". It will also have momentum based on
the "coefficient of restitution" (which describes the
wall-ball interaction). Use conservation of momentum to get
the rest.
Hi, and thank you for your prompt reply,
I am mostly interested in this forcing function rather than the
momentum or the reflecting force from the box boundary.
(Imagine that the box is inifinetly large so is doesn't
actually come in touch with the boundaries).
Would it be possible for you to give me a basic formulation of
this forcing function?
I moved your response to the end. It is a lot easier to read,
since posts here are archived for years.
You indicated you were shaking the box. *You* are the forcing
function. If you are strong, the box and ball light, then you
could simply apply sin( omega * t) as a displacement of the top
and bottom of the box. If you are modelling little pills in a
vibrating hopper, things could be more complex.
David A. Smith
.
|
|
|
|
| User: "Bjoern Feuerbacher" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
11 Mar 2005 03:54:55 AM |
|
|
Vasileios Zografos wrote:
Hi, and thank you for your prompt reply,
I am mostly interested in this forcing function
Then you have to describe in more detail how exactly you do the
shaking.
rather than the momentum or
the reflecting force from the box boundary. (Imagine that the box is
inifinetly large so is doesn't actually come in touch with the boundaries).
Is the box filled with air or another gas or liquid? If not, you can
shake the box as long as you want - if the ball does not touch the
boundaries of the box, it won't change its state of motion (i.e.
it will accelerate downwards due to gravity.
Would it be possible for you to give me a basic formulation of this forcing
function?
No, since not enough information was provided by you.
[snip]
Bye,
Bjoern
.
|
|
|
| User: "Mike Yarwood" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
11 Mar 2005 04:45:08 AM |
|
|
"Bjoern Feuerbacher" <feuerbac@thphys.uni-heidelberg.de> wrote in message
news:d0rptf$h2f$3@news.urz.uni-heidelberg.de...
Vasileios Zografos wrote:
Hi, and thank you for your prompt reply,
I am mostly interested in this forcing function
Then you have to describe in more detail how exactly you do the
shaking.
rather than the momentum or the reflecting force from the box boundary.
(Imagine that the box is inifinetly large so is doesn't actually come in
touch with the boundaries).
Is the box filled with air or another gas or liquid? If not, you can
shake the box as long as you want - if the ball does not touch the
boundaries of the box, it won't change its state of motion (i.e.
it will accelerate downwards due to gravity.
Would it be possible for you to give me a basic formulation of this
forcing function?
No, since not enough information was provided by you.
[snip]
Bye,
Bjoern
Hi Vasileios,
move the box+ball_in_the_hole upwards at some velocity v , now decelerate
the box faster than g will do. If the ball is not stuck to the bottom of
the hole it will decelerate less rapidly than the box and if the hole is
shallow enough , will jump out of the hole. Note that v can be -ve or zero
, it still works o.k.
Best of Luck - Mike
.
|
|
|
|
|
|
|
| User: "Bjoern Feuerbacher" |
|
| Title: Re: newbie question on kinetic or vibrational energy (force) |
11 Mar 2005 03:50:49 AM |
|
|
Vasileios Zografos wrote:
Hi, first of all let me say that I am no physicist, and my knowledge of
physics stops at high-school. My scientific field is quite different
(computer vision).
Now, this of the following example. I have a little glass box, and inside I
have a metal sphere. I shake this box and this sphere "jumps" around inside
the box. Imagine if you will, these popular games, where you have to shake
the box and make the ball (sometimes many balls) jump into a hole.
I have a question regarding the forces (or energies if you like) that are
exerted on the ball as we shake the box.
Forces are exerted. Energies aren't.
Of course we have the gravitational
force (they call it potential force?) and some kind of vibrational force,
that we exert to the box and the box in turn exerts to the sphere. I assume
that this force become the ball's kinetic energy.
More correctly: this force changes the ball's energy. As does the
gravitational force.
Additionally, you have to take into account that the walls of the
box exert also a force on the ball when they touch.
What I am looking for is a really basic formulation (I can deal with
derivatives and partial pdfs) for that vibrational force.
Depends on how exactly you do the shaking!
E.g. if you simply move the box up and down periodically,
the "vibrational" force would be something like
F(t) = F_0 sin(2 pi f t + phi) e_z,
where F_0 is the amplitude, f the frequency, t is time, phi is
a possible phase, and e_z the unit vector in z direction (up).
Can somebody help me please?
I know that the kinetic energy Ek=1/2mv^2 and that the potential energy that
the ball has is Ep=mgh...but what about that vibration?
The "vibrational" force causes changes in the kinetic energy of the
ball. You could treat this with formulas for elastic scattering
(assuming that there are no heat losses and the like when the ball
bounces off the wall).
Bye,
Bjoern
.
|
|
|
|
|
Related Articles |
|
|
