Confustion about circular motion

Announcements Posted on
    • Thread Starter
    Offline

    3
    ReputationRep:
    the formula F=m x omega^2 r shows that with greater radius the centripetal force is more

    but F=v^2 x M/r shows that its inversely proportional?

    so which one is it and what am I missing
    Offline

    3
    ReputationRep:
    Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.


    Just quoting in Danny Dorito so she can move the thread if needed :wizard:
    Spoiler:
    Show
    (Original post by Danny Dorito)
    x
    Offline

    3
    ReputationRep:
    Joinedup mik1a perhaps one of yous can help.
    Offline

    2
    ReputationRep:
    (Original post by NatoHeadshot)
    the formula F=m x omega^2 r shows that with greater radius the centripetal force is more

    but F=v^2 x M/r shows that its inversely proportional?

    so which one is it and what am I missing
    They're the same. Omega is v/r. If you increase the radius, at the same speed, omega will decrease with radius, leading its square to decrease the acceleration overall.
    Offline

    3
    ReputationRep:
    both formulae are valid. i personally prefer the one without omega
    Offline

    2
    ReputationRep:
    (Original post by NatoHeadshot)
    the formula F=m x omega^2 r shows that with greater radius the centripetal force is more

    but F=v^2 x M/r shows that its inversely proportional?

    so which one is it and what am I missing
    When you say that F = mrw^2 shows that a greater r means a greater F, I assume that you mean for a constant w.

    But v = rw, so if you have a bigger r and a constant w, you also get a bigger v. When you look again at F = mv^2/r, the v is squared, so the bigger v has a much bigger effect than the bigger r, giving you a bigger F overall.

    Let's look at a more specific case. If there is a force of F for a particular m, r and w, let's see what happens when we double r but keep w the same. The new force is m(2r)w^2 = 2mrw^2 = 2F, so the centripetal force has doubled.

    As v = rw, doubling r will also double v, for a fixed w.

    So, the new force is also m(2v)^2/2r = 4mv^2/2r = 2mv^2/r = 2F, so again, the centripetal force has doubled. You get the same answer both ways.

    Replace 2r with kr, where k is any constant, and the same argument applies.
    Offline

    3
    ReputationRep:
    Both equations are still correct, but it does look confusing at first.

    The key is that v = wr, so the v^2 term in the second equation is 'hiding' an r^2 term inside it (since v^2 = w^2*r^2). If you substitute v = wr into the second equation and then cancel, you'll get the first equation.
    Offline

    3
    ReputationRep:
    (Original post by the bear)
    both formulae are valid. i personally prefer the one without omega
    But calculating omega makes it easier for other parts of the question bear.
    Just recall how many equations omega features in
    Spoiler:
    Show
    Plus omega is wonderful :love:
    Offline

    3
    ReputationRep:
    (Original post by CheeseIsVeg)
    But calculating omega makes it easier for other parts of the question bear.
    Just recall how many equations omega features in
    Spoiler:
    Show
    Plus omega is wonderful :love:
    you are getting confused with omega fish oils :spank:
    Offline

    3
    ReputationRep:
    (Original post by the bear)
    you are getting confused with omega fish oils :spank:
    But they're so
    Spoiler:
    Show
    :daydreaming:
 
 
 
Write a reply… Reply
Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: October 24, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR
Poll
How are you feeling about doing A-levels?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Sponsored content:

HEAR

HEAR

Find out how a Higher Education Achievement Report can help you prove your achievements.

Groups associated with this forum:

View associated groups

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.