What is the difference between friction and rolling resistance?

In summary, the problem is asking for the force the cyclist provides, not the net force. When the coefficient of friction is not given, what force does the cyclist provide?
  • #1
paulimerci
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Poster has been reminded to always show their work when posting schoolwork problems
Homework Statement
A 65 kg cyclist on a 10 kg bicycle is moving uphill on a 9° slope. How much force does he provide
if the bicycle slows at a rate of 0.3 m/s2?
Relevant Equations
Applied force - frictional force - parallel force component due to gravity = ma
How to find frictional force when coefficient of friction is not given?
 

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  • #2
If the bicycle wheels roll without slipping or are not on the verge of slipping, the coefficients of friction are irrelevant. You have the acceleration, so what is the net force on the bicycle + cyclist system? What is the net force just on the bicycle?
 
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  • #3
So you mean there is no frictional force acting on the system?
 
  • #4
paulimerci said:
So you mean there is no frictional force acting on the system?
Not what he means.

He said that you don't need to know the frictional force to solve this problem.
 
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  • #5
SammyS said:
Not what he means.

He said that you don't need to know the frictional force to solve this problem.
But it’s asking for the force the rider provides, not the net force.

I feel like “ignore friction” should be right in the problem statement on this one?
 
Last edited:
  • #6
paulimerci said:
Homework Statement:: A 65 kg cyclist on a 10 kg bicycle is moving uphill on a 9° slope. How much force does he provide
if the bicycle slows at a rate of 0.3 m/s2?
Relevant Equations:: Applied force - frictional force - parallel force component due to gravity = ma

How to find frictional force when coefficient of friction is not given?
@paulimerci -- Please post a new thread with this problem and show your work.

As you can see from the replies, this is most likely not a problem of something sliding up or down an inclined plane with sliding friction coming into play. If a bicyclist is pedaling up a slope and slowing down, there is a force that the bicyclist is applying by pedaling but it's not enough force to keep them from slowing down on the slope. So in your FBD, you should leave off any retarding force due to sliding friction, and focus on what force the bicyclist needs to exert to result in the motion specified in the problem.
 
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  • #7
Disregard post #5. I think I see what @kuruman was driving at now that I've written it down.
 
  • #8
paulimerci said:
Homework Statement:: A 65 kg cyclist on a 10 kg bicycle is moving uphill on a 9° slope. How much force does he provide
if the bicycle slows at a rate of 0.3 m/s2?
Relevant Equations:: Applied force - frictional force - parallel force component due to gravity = ma

How to find frictional force when coefficient of friction is not given?
You are suffering from a common confusion between friction and rolling resistance. The relevant equation posted takes friction as always something opposing motion, which is incorrect.
Please read https://www.physicsforums.com/insights/frequently-made-errors-mechanics-friction/ before reposting the thread .
 
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1. What are Newton's Laws of motion?

Newton's Laws of motion are three fundamental principles that describe the behavior of objects in motion. They were first described by Sir Isaac Newton in his book "Philosophiæ Naturalis Principia Mathematica" in 1687.

2. What is the first law of motion?

The first law of motion, also known as the law of inertia, states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity, unless acted upon by an external force.

3. What is the second law of motion?

The second law of motion states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to its mass. This can be mathematically expressed as F = ma, where F is the net force, m is the mass of the object, and a is the acceleration.

4. What is the third law of motion?

The third law of motion, also known as the law of action and reaction, states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object will exert an equal and opposite force back on the first object.

5. How do Newton's Laws of motion apply to everyday life?

Newton's Laws of motion can be observed in many everyday situations, such as when a car accelerates or when a person jumps. They also form the basis of many engineering and technological advancements, such as the design of airplanes and rockets. Understanding these laws can also help us predict and explain the motion of objects in our daily lives.

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