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Question
Hello  sir

Sir As you explained that line of riction defination. Sir in that you replied that it is force which stops the motion. But sir my one doubt sir what stops the motion of an object. When ball is moving on the ground, any force stops it. Exactly what stops it . If force stops it then from where that force appear? Is already an force present inside the earth.?

Sir i asked that expaination of defination of friction in my previous post because i want to ask the above question i asked that expaination.

Answer
Friction stops moving objects which are sliding.  Friction is a force.  This force occurs between any two surfaces.  Much has been written about such a basic concept, I don't need to re-invent it all here.  See this page for details:
http://www.virginia.edu/ep/SurfaceScience/friction.html

If you need further information, I suggest you just use a google search and read the carefully thought-out references that already exist.  There's no need to come to an expert forum when friction is already well-explained.

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

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Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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