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# Physics/fundamental forces

Question
Hi,

I read that there are only four fundamental forces in nature. When I push an object, mechanical force is applied. How mechanical energy gets created when according to law of conservation of energy cannot be created. There are other forces like centrifugal, centripetal forces etc but still why scientists say that there are only 4 fundamental forces. Please clarify.

Energy can be converted from one form to another.  What you experience as a force is actually microscopically local electrostatic forces.  The forces you mention are all based in electroststatics (when you displace the charged particles that make up atoms and molecules, it results in forces).  The other ones are, obviously, gravitational and the two nuclear forces that exist on very short length scales.

Let's take the example of swinging something around on a string.  The tension (a force) in the string *is* the centrpetal (centrifugal is a word most scientists don't use for some reason) force that keeps the object moving in a circle and not flying off in a straight line.  That force is based on stretching/repositioning of molecules in the string.  That creates displacement along the string of charged particles in those molecules, causing electrostatic attraction on the nanometer length scale.  That's tension.  That's why it pulls at both sides, positive and negative attracting one another.  Same thing with the internal stresses that transfer the forces from the attachment point of the string to the other molecules making up the object.

Yes, when you look at the ultimate forces, there are only four known forces.  The rest are just extensions of those on a macroscopic scale.

Physics

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#### Dr. Stephen O. Nelson

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