Expansion of a gas against a piston

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SUMMARY

The discussion focuses on the work done by a gas expanding against a piston and its interaction with gravity. It is established that the work done by the gas against gravity is equal to the change in gravitational potential energy, represented by the formula mgh, where h is the vertical displacement. However, this gravitational work is negligible in practical applications, often less than the error margin in engine performance measurements. Additionally, the discussion highlights that during the exhaust stroke, the piston exerts significant work on the gas, further influencing the overall dynamics.

PREREQUISITES
  • Understanding of thermodynamics principles, particularly work and energy transfer.
  • Familiarity with the concept of gravitational potential energy (mgh).
  • Knowledge of piston-cylinder systems in engine mechanics.
  • Basic grasp of measurement errors in experimental physics.
NEXT STEPS
  • Research the principles of thermodynamics related to gas expansion and work.
  • Study the effects of gravitational potential energy in mechanical systems.
  • Explore the dynamics of piston-cylinder interactions in internal combustion engines.
  • Investigate measurement techniques and error analysis in engine performance testing.
USEFUL FOR

Mechanical engineers, physics students, and professionals involved in engine design and performance analysis will benefit from this discussion.

deadscientist
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So let's say a gas is doing some work against a piston and decreasing its internal energy. Does the gas also do work against gravity if it is expanding in the positive y direction? If so would it even be measurable? Thanks for the help
 
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Yes; the work done is equal to the change in gravitational potential energy i.e. mgh, where h is the vertical movement of the centre of gravity. However this amount is negligible in just about any context, certainly less then the error in any realisable model or measurement of engine performance. And immediately after the combustion stroke there will be a lot more work done on the gas by the piston in the exhaust stroke.
 
Yes, and yes
 

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