Re: Hydraulic Presses and Force
- From: "Dennis B" <Utopian@xxxxxxxx>
- Date: 27 Jun 2006 08:30:43 -0700
Dennis B wrote:
A hydraulic press is supposedly capable of amplifying force. For
example, 1 dyne of input force can supposedly be converted into 10
dynes or even 100 dynes of output force. In a hydraulic press the
supposed increase of force is offset by a decrease in the distance the
output piston travels. The output is dependent upon the (exposed)
surface area of the piston (and input force). As the volume or capacity
of the output piston chamber increases (and the exposed surface area of
the piston as well), the distance which the output piston travels will
decrease in response to the input force (presuming the input remains
constant). Force is determined by measuring the displacement of a mass
(as well as the time involved for the displacement to occur). Since the
distance a piston travels is dependent upon the volume or capacity of
the piston chamber (as well as input force), the distance travelled by
two different (output) pistons as a result of a given input force (1
dyne for example) will not be the same if the volume or capacity of the
output piston chambers are different (for example if the exposed piston
surface area of one is 10 cm^2 and 100 cm^2 in the other). Yet, the
total volume of fluid displaced (1 cm^3) is the same for both pistons.
In other words, the amount of mass (i.e., the water) displaced in
response to a given input force (1 dyne in this example) is the same.
Thus, wouldn't the output force of both pistons be the same,
considering that force is measured by the displacement (or
acceleration) of a mass (such as the water inside the piston in this
case)? Undeniably, the total energy remains the same (ignoring losses
due to friction, etc.), although the energy density must decrease at
the output for the same reason that the total energy density of a fluid
accelerating through a tube of varying diameter changes, while the
total energy remains the same (ignoring losses). The definition of
force is that which causes acceleration of a body. Force would
therefore appear to be synonymous with the definition of "energy". So,
how is it that the input force increases while the input energy density
decreases in the case of a hydraulic press? One may be inclined to
argue that the energy density does not decrease as the volume/capacity
of the output piston chamber (or circumference of the tubing)
increases. Yet, the energy density does in fact decrease as the volume
(capacity) of the piston chamber or circumference of the tubing
decreases, for the energy must expand to occupy a larger volume of
space. Thus, I would expect that the force would decrease as well, just
as the ram pressure (and velocity) of an accelerating fluid decreases
as the circumference of the tube in which it flows increases. To use an
example, I would expect that a force of 1 dyne applied to a piston with
an exposed surface area of 1 cm^2 would be converted into a force of .1
dyne cm^2 in an output piston with an exposed surface area of 10 cm^2.
Correction:
To use an example, I would expect that a force of 1 dyne applied to a
piston with an exposed surface area of 1 cm^2 would be converted into a
force of .1 dyne/cm^2 in an output piston with an exposed surface area
of 10 cm^2.
-Dennis B
.
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