Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hi

    The equation for the frictional force for OCR M1 is:

    F=uR

    Where;

    F= the maximum frictional force
    u= coefficient of friction
    R= normal reaction force

    We are taught that the frictional force is equal to the driving force unless the driving force is greater than uR, in which case the frictional force is equal to uR.

    My question is that if I apply a driving force to an object (greater than uR) and then release that force, there will be an initial frictional force but then won't the friction be equal to zero because my driving force is now zero? And therefore the object just moves at a constant velocity forever?

    Have I missed something or is this just a simplified equation?
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by JAVM)
    Hi

    The equation for the frictional force for OCR M1 is:

    F=uR

    Where;

    F= the maximum frictional force
    u= coefficient of friction
    R= normal reaction force

    We are taught that the frictional force is equal to the driving force unless the driving force is greater than uR, in which case the frictional force is equal to uR.

    My question is that if I apply a driving force to an object (greater than uR) and then release that force, there will be an initial frictional force but then won't the friction be equal to zero because my driving force is now zero? And therefore the object just moves at a constant velocity forever?

    Have I missed something or is this just a simplified equation?
    What you have been taught doesn't always work, as your example shows. You can probably imagine that if you were to release the force on a moving object then it would obviously decelerate due to friction.

    In M1 for an object in motion (accelerating, deccelerating or constant speed), the friction will always be at its maximum, independedent of what the driving force is. So F=\mu R for a moving object.

    In reality static friction and kinetic/dynamic friction are often different but in M1 you can assume that F=\mu R when an object is moving and F\leq \mu R for a stationary object.
    • Thread Starter
    Offline

    0
    ReputationRep:
    Ok great, thank you. That makes sense.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.