What is a machine?

This question was asked several times through askphysics, but I was thinking whether or not to answer such a simple question. But when I pondered, I felt that there is something which I can tell the world through the answer to this post.

If you search, you can find several definitions to “Machine”

To be quite simple, A machine is any device which makes human efforts easier. It may be used to magnify human capabilities, physical or psychological. It may be partially or completely automated.

A machine is helpful to save human effort, not energy. There are even cases where the machine is not providing any mechanical gain of effort, but changes its direction so that the effort can be conveniently applied.


Double Slit Experiment and Quantum Mechanics

In regards to the double slit experiment with detectors and firing electrons one at a time ….a lab is set up where we run 100 separate experiments where a single electron is fired through a double slit say 500 times each cycle to build a pattern.  Beforehand the computer will make a random heads or tales decision as to whether or not the next cycle will be run with the detectors on or off. So statistically 50% of the time the detector will be off and no one will know beforehand we will only know after the fact by reviewing the data stored in the computer as to whether or not the next consecutive cycle was run with the detector on or off. 

There’s a catch….the computer is required to make a second random heads or tales decision to entirety erase all the data from an individual experiment so statistically for half of the 100 individual experiments (or cycles) we won’t know if the detector was on or off.   In only 50% of the individual runs can we say for certain if the cycle was run with the detectors on or off. 

Out of 100 runs how many particle behavior patterns would you expect to see and how many wave patterns would you expect to see.

Optics question

Hello,I dont know how to do this short exercise,I mean it does not make any sense.The only thing i know  is that the answer is 3.3cm  but i cant do the procudure finding the same result.This is the exercise:
A concave mirror makes a 3 cm image of a 6 cm object when the object is placed 10 cm from the mirror. What is the focal length of the mirror?

It really would help me if you lend me a hand on this.
many thanks

Daniel posted



Maxwell’s equations for electromagnetic waves

Physicists illustrate EM waves as perpendicular E and M waves. That seems consistent. What does not make sense is the illustrations showing the E wave phase equal to the M wave. This seems to violate Maxwell’s equations.
The largest E potential would seem to be when the M wave is at a maximum of di/dt when the M wave crosses the zero axis. When maximum changes to the E wave magnitude occur as the E wave magnitude crosses the 0 axis then would not this correspond to the maximum in the M wave?
The wave nature of electromagnetic waves, as a consequence of Maxwell’s equations, makes sense except it would appear that the E and M waves should have a 90 degree separation. What am I missing?

John Varga asked

The following links may help you


Electromagnetic Waves and their Properties


A Physicist Driver confusing Police

A driver is stopped for running a red light. trying to avoid a ticket, the driver tells the police officer that because of the Doppler shift, the red light (650 nm) was blueshifted to a green light (470 nm). what would the drivers speed need to be for this to be true


Asked Sabnna

Would an underground nuclear explosion generate an Electromagnetic pulse?

Would an underground nuclear explosion generate an EMP? If so, how far would it be likely to travel?

Asked Daniel

You can get answer to your question here. If you need further clarification, please post as comment to this post.\



The indigenous Cryogenic Engine of India

The cryogenic engine used in indian rocket gslv is also called as?

Asked Shaaru

Answer: CE 7.5 was the first successful engine and CE-20 is the Cryogenic Engine developed by the Liquid Propulsion Systems Centre, a subsidiary unit of ISRO developed to power the upper stage of the Geosynchronous Satellite Launch Vehicle MK III  also referred to as the Launch Vehicle Mark 3 (LVM3).  It is the first Indian cryogenic engine to feature a gas-generator cycle   References ISRO website https://www.isro.gov.in/gslv-d5-gsat-14/indigenous-cryogenic-engine-and-stage    

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