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Answers to Readers' Questions on Physical Science:

Friction Equation

The following 2 comments and questions have been sent in. They are listed according to date.

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• What is resultant force in friction?
• Sees problems in lesson

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What is resultant force in friction?

Question

November 11, 2008

what is resultent force in friction

navjot - India

16777

Answer

The resultant force is what acts on a body. Friction acts in the opposite direction to the resultant force. Often the resultant force is a combination of forces.

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Sees problems in lesson

Question

May 31, 2008

Your chapter on friction has two problems:

1) You say "force required to push the box along the floor is 70 pounds" -- "pounds" is not a measurement of force. "Newtons" is a measurement of force; "pounds" is a measurement of mass.

2) Question 2 asks what happens to the normal force as a function of incline. The problem is that, if the normal force is exerted beacuse of gravity, answer c is right, but if the normal force is exerted because of some independent pressure, answer b is right. To make the question unambiguous, you have to specify whether gravity is the source.

Jon - USA

16018

Answer

A slug is the unit of mass in the English system, while a pound is the unit of weight or force. Likewise, in the metric system, a kilogram is a unit of mass and the Newton is the unit of weight or force.

But you are correct about Question 2 being ambiguous. That was a careless mistake on my part. I added that the "...normal force, as affected by gravity" and corrected the page.

Thanks for pointing that out to me.

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