Determining Linear Frequency: Velocity, Stroke & More

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Discussion Overview

The discussion focuses on determining linear frequency in relation to rotational frequency, specifically in the context of a piston in an engine. Participants explore the relationship between velocity, stroke length, and frequency, considering how these factors interact in mechanical systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks how to determine linear frequency compared to rotational frequency, specifically for a piston, and questions the role of velocity and stroke length in this determination.
  • Another participant defines linear frequency as the number of cycles per second and explains that a piston completes a cycle by returning to its starting position, relating this to mechanical conversions between piston strokes and rotations.
  • A participant expresses a realization that the piston frequency should match the engine's RPM, suggesting a direct correlation between the two.
  • It is noted that the engine's RPM represents the number of cycles per minute of the crankshaft, which is also applicable to the piston, and that speed may not be a determining factor since different paths can yield the same RPM.

Areas of Agreement / Disagreement

Participants generally agree on the relationship between piston frequency and engine RPM, but there is some uncertainty regarding the role of velocity and stroke length in determining linear frequency.

Contextual Notes

Some assumptions about the mechanics of pistons and the definitions of frequency may not be fully articulated, and the discussion does not resolve how velocity is factored into the frequency calculation.

cgaday
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How would you go about determening a linear frequency, compared to that of a rotational frequency. For instance, determining the frequency of a piston in cylcles/second?

I would assume velocity has to be involved, and the length of the stroke. How is velocity put into play, is it constant, or does it go in one direction, stop at 0 velocity, and then immediatly speed back up. Thats what it would do in the engine, but how do you account for this?

Help please!
 
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A lfrequency is just that, the number of cycles ( oscilations, rotations or more complex motions) per second. If a piston starts at a position, then moves and comes back again to it's starting position then it completed a cycle.

If you consider the fact that piston stokes can be mechanically converted to rotations then it is very easy to understand the concept. Like in a crankshaft and connecting rod, where an engine has the same frecquency for the piston as for the crankshaft.
 
Ah hah, thinking too complicated gets the best of me again. Essentially the piston would have the same frequency as the RPM's that the engine is undergoing correct?
 
cgaday said:
Ah hah, thinking too complicated gets the best of me again. Essentially the piston would have the same frequency as the RPM's that the engine is undergoing correct?

Yes, the engines RPM is the number of cycles(rotations) / minute of the crankshaft, which is the same RPM ( although no rotation this time) of the piston. Speed does not matter as for the same frequency to pistons can travel 2 different paths (one longer one shorter) and still have the same rpm.
 

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