I want to clear my doubts (friction and work)

  • Thread starter shalini_monalisa
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In summary: The work done by friction is zero because the point of application of the force and the friction force are on the same object, and the distance between them is constant.
  • #1
shalini_monalisa
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i read in a book-'work is done when a force moves its point of application.this involves movement of the object on which force acts and movement of the force itself.'
when this is true ,then why is the work done by friction on pencil zero when pencil makes a circle on a page ?
i assume that tip of pencil (point of app.of force) and friction both are moving.please clarify where i am going wrong.
 
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  • #2
shalini_monalisa said:
then why is the work done by friction on pencil zero when pencil makes a circle on a page ?
Why do you think the work done is zero?
 
  • #3
Doc Al said:
Why do you think the work done is zero?
I am not saying the work done by friction is zero. it is answered thus in the book.
 
  • #4
shalini_monalisa said:
I am not saying the work done by friction is zero. it is answered thus in the book.
Can you give an exact reference? I'm curious as to what the book says.
 
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  • #5
You may be confused about the true meaning of ' when a force moves it's point of application ' .

When drawing a circle the point of application of the pencil force appears to end up back where it started and it is easy to infer from this that no net movement of the point of application of the force has taken place and therefore no work has been done .

That inference is completely wrong though . Can you tell us why ?
 
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  • #6
Is there an assumption of the work done being vector or scalar, as if it is scalar then this may infer that work has been done, while vector may not have a net work done.
 
  • #7
Please use correct capitalization and punctuation in your questions.
Moving in a circle is still moving, even if you end up in the same place.
 
  • #8
Khashishi said:
Please use correct capitalization and punctuation in your questions.
Moving in a circle is still moving, even if you end up in the same place.
However the distance has a positive value, while the displacement does not.
 
  • #9
StanEvans said:
Is there an assumption of the work done being vector or scalar, as if it is scalar then this may infer that work has been done, while vector may not have a net work done.
Work is a scalar quantity.

StanEvans said:
However the distance has a positive value, while the displacement does not.
The work done is the integral of force*displacement over the path (##\int \vec{F}\cdot d\vec{s}##).
 
  • #10
State the pencil thing clearly
 

1. What is friction and how does it work?

Friction is a force that resists the relative motion between two surfaces that are in contact. It works by converting kinetic energy (motion) into heat energy through the microscopic interactions between the surfaces.

2. What are the types of friction?

There are four main types of friction: static, sliding, rolling, and fluid. Static friction occurs when two surfaces are not moving relative to each other. Sliding friction occurs when two surfaces are moving against each other. Rolling friction occurs when an object is rolling over a surface. Fluid friction occurs when an object moves through a fluid (such as air or water).

3. How does friction affect the amount of work done?

Friction can make it more difficult to do work by creating a force that opposes the direction of motion. This means that more work must be done to overcome the force of friction, resulting in an increase in the amount of work done.

4. Can friction be beneficial?

Yes, friction can be beneficial in some situations. For example, it allows us to walk without slipping and helps vehicles to have traction on the road. In some machines, friction is necessary for their function, such as brakes in cars and gears in bicycles.

5. How can we reduce friction?

There are several ways to reduce friction, including using lubricants, polishing surfaces, and using ball bearings. Lubricants, such as oil or grease, create a thin layer between two surfaces and reduce the amount of friction. Polishing surfaces makes them smoother, reducing the amount of contact between the surfaces. Ball bearings use rolling friction instead of sliding friction, which reduces the amount of friction and allows for smoother movement.

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