## Physics Chapter 2 - Friction

SungHoonPark97
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Joined: Tue May 22, 2018 12:16 pm

### Physics Chapter 2 - Friction

In the textbook, it divides friction force into two components: static and kinetic.

The textbook states that the equation for static friction = (coefficient of static friction)*N(aka applied force)
The textbook states that the equation for kinetic friction = (coefficient of kinetic friction)*N(aka Normal force)

Is this correct? I thought N was normal force for both cases.

In question 3 of chapter 2's independent questions, the explanation states that N is normal force and NOT applied force. So, I was wondering which one is the typo?
NS_Tutor_Katelyn
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### Re: Physics Chapter 2 - Friction

SungHoonPark97 wrote:In the textbook, it divides friction force into two components: static and kinetic.

The textbook states that the equation for static friction = (coefficient of static friction)*N(aka applied force)
The textbook states that the equation for kinetic friction = (coefficient of kinetic friction)*N(aka Normal force)

Is this correct? I thought N was normal force for both cases.

In question 3 of chapter 2's independent questions, the explanation states that N is normal force and NOT applied force. So, I was wondering which one is the typo?
Kinetic friction is the simpler of the two forces: it’s always equal to the coefficient times the normal force.

Static friction is a bit more complicated. The coefficient multiplied by the normal force will give you the maximum possible value of static friction, but the actual value of static friction is always equal to the force that it opposes. So in a scenario where I exert 10 N force on a 10 kg box resting on a flat surface with a coefficient of static friction equal to 0.5, the force of static friction will be equal to 10 N, even though the maximum possible value of static friction would be 50 N.

Let me know if that helps!

-Kate
Katelyn Sawyer
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SungHoonPark97
Posts: 11
Joined: Tue May 22, 2018 12:16 pm

### Re: Physics Chapter 2 - Friction

Thank you! That helps a lot!
ESTEBAN227
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Joined: Thu Aug 23, 2018 11:24 am

### Re: Physics Chapter 2 - Friction

In your response you stated that for static friction, you multiply the coefficient of static friction with the normal force to find the maximum possible value of static friction. But the actual value of static friction is always equal to the force that it opposes. So in the example you provided, a 10 N force is applied on a 10 kg box resting on a flat surface with a coefficient of static friction equal to 0.5, the force of static friction will be equal to 10 N, does the equation for Fstatic not multiply the coefficient of static friction with the applied force (as stated in the book)? Because then Fstatic would = 5N? or do you just disregard the equation and Fstatic is just equal to the force applied to it?
NS_Tutor_Katelyn
Posts: 157
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### Re: Physics Chapter 2 - Friction

ESTEBAN227 wrote:In your response you stated that for static friction, you multiply the coefficient of static friction with the normal force to find the maximum possible value of static friction. But the actual value of static friction is always equal to the force that it opposes. So in the example you provided, a 10 N force is applied on a 10 kg box resting on a flat surface with a coefficient of static friction equal to 0.5, the force of static friction will be equal to 10 N, does the equation for Fstatic not multiply the coefficient of static friction with the applied force (as stated in the book)? Because then Fstatic would = 5N? or do you just disregard the equation and Fstatic is just equal to the force applied to it?
You disregard the equation. Static friction is always equal to the force that it opposes, up to a maximum possible value given by the equation.

-Kate
Katelyn Sawyer
Senior Tutor
katelyn@nextsteptestprep.com