Spring Displacement in Moving Part: Constant Pressure?

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Discussion Overview

The discussion revolves around the dynamics of a spring under constant pressure, particularly focusing on the displacement of the spring in a moving part over time. Participants explore the implications of mass, acceleration, and forces acting on the spring, considering both theoretical and practical aspects of the problem.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning
  • Experimental/applied

Main Points Raised

  • One participant questions how to determine spring displacement when pressure is constant, particularly in the absence of mass.
  • Another participant raises the implications of Newton's second law regarding acceleration when mass is negligible or absent.
  • There is a discussion about the acceleration of the spring's center of mass and its relationship to the net force acting on it.
  • Participants propose modeling the spring as a series of ideal massless springs connected by point masses to analyze the motion under applied forces.
  • One participant suggests that the acceleration of the free end of the spring could be approximated as double that of the center of mass, though this approximation may ignore oscillations within the spring.
  • Another participant expresses a need to model a single-effect piston, indicating a practical application of the discussed concepts.
  • There is curiosity about implementing a differential equation to describe the motion of the spring, with a request for guidance on this mathematical approach.
  • One participant mentions calculating acceleration during oil replenishment in a specific context, seeking clarification on how to approach this calculation.

Areas of Agreement / Disagreement

Participants express various viewpoints on the dynamics of the spring, with no clear consensus reached on the best approach to model the system or the assumptions involved. Multiple competing views on the treatment of mass and acceleration remain present throughout the discussion.

Contextual Notes

Limitations in the discussion include assumptions about mass distribution, the treatment of oscillations, and the applicability of approximations made regarding acceleration. The mathematical steps required to derive the differential equations are not fully resolved.

Andrea Vironda
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hello, I'm new here
according to this scheme:
3ZPZqGN.jpg

i would to know, if the pressure is constant, the spring displacement in the moving part in function of time.
the square is without mass, so i thought to use the energy approach, but i don't know how to consider acceleration
 
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If there is a force but no mass or an extremely small mass, what happens to acceleration? What does Newton's second law say?
 
The acceleration is Very high. But in this case The only mass i have is The spring, which is fixed on one extremity. I don't know how to consider this
 
Andrea Vironda said:
The only mass i have is The spring, which is fixed on one extremity.
The acceleration of the centre of mass times the mass is the net force.
 
Andrea Vironda said:
The acceleration is Very high. But in this case The only mass i have is The spring, which is fixed on one extremity. I don't know how to consider this
One way of considering it is to imagine the spring as a being a chain of ideal massless springs connected via ideal pointlike masses. As you apply force to one end of the spring, the masses near the force end move more and the masses near the fixed end move less.

In principle, you could use Newton's laws, write down an equation for the motion of each of the masses and solve them all.

If one imagines the limit of the process as the length of the component springs get shorter and shorter, the number of component springs get higher and higher and the masses get smaller and smaller, you end up with a continuous spring.

You can apply Newton's laws to obtain a differential equation defining the acceleration of each part of the spring in terms of the local mass density and the local tension gradient. With some simplifying assumptions you can solve this and obtain things like a wave equation.

[Or you could do as @A.T. suggests and imagine the spring as having its mass concentrated in the center. Way easier and probably accurate enough for your purposes].
 
A.T. said:
The acceleration of the centre of mass times the mass is the net force.
can i assume the spring free end acceleration as the double of the center of mass acceleration?

jbriggs444 said:
You can apply Newton's laws to obtain a differential equation defining the acceleration of each part of the spring in terms of the local mass density and the local tension gradient. With some simplifying assumptions you can solve this and obtain things like a wave equation.
i'm curious but I'm not able to implement this differential equation. can you give me a sketch?
 
Andrea Vironda said:
can i assume the spring free end acceleration as the double of the center of mass acceleration?
As an approximation, that ignores oscillation within the spring.
 
it's good, because i have to modelize a single-effect piston
 
A.T. said:
As an approximation, that ignores oscillation within the spring.
if i substitute i find i have ~1600g. i think this is the acceleration i receive if i cut the pressure supply outright.
if i have to calculate the acceleration the spring have during the room oil replenishment, how can i do? only for the forward stroke.
 

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