Hydraulic Press: Keep an Energy Ledger

Include changing stored energy before reporting efficiency.

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For a stated interval, input energy = useful output + losses + increase in stored energy. A negative storage change means previously stored energy is being released. Do not infer perpetual motion from one short interval. Use diagrams and calculations only; never build or operate a press for this activity.

Worked example

During loading, 100 J enters, 55 J is useful output and 15 J is transferred as heat. Stored energy increases by 30 J. Real systems may store energy in elastic parts, compressed liquid or gas accumulators.

During one interval, 100 joules of input becomes 55 joules of useful output, 15 joules of heat, and a 30-joule increase in stored energy.

Would you believe it?

Two points in still liquid can have different pressures if they are at different depths. Transmitting a pressure change does not make all pressure readings identical.

OpenStax: pressure and depth

Question 1 What is the increase in stored energy in the example? 30 J 40 J 70 J

Question 2 Later, input is 10 J, heat loss 5 J, and storage falls by 30 J. Useful output? 15 J -25 J 35 J

Question 3 Does 35 J output from 10 J new input violate conservation here? No, force has no connection to energy No, storage supplied energy Yes, energy was created

Question 4 When may a whole-cycle efficiency omit the storage-change term? When net stored-energy change is zero Whenever output force is large Whenever pressure is measured

Question 5 Does switching a machine off prove that all stored energy is gone? Yes Only if the display is dark No

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