Go Back   Physics Help Forum > College/University Physics Help > Advanced Mechanics

Advanced Mechanics Advanced Mechanics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Aug 7th 2017, 02:42 PM   #1
j95
Junior Member
 
Join Date: Aug 2017
Posts: 3
Determining Mass from Momentum

Is it possible to determine the mass of an object (i.e Bicycle) given the (Coefficient rolling resistance), (Initial Velocity) and the (Deceleration). Given that you are able to change the (Coefficient Rolling Resistance) and from this determine a new (Deceleration). Wind resistance and internal frictions are neglected. If so how?

This is for a personal project where for one part I need to determine the weight of the bicycle, by a simple roll test.

Last edited by j95; Aug 8th 2017 at 01:03 PM.
j95 is offline   Reply With Quote
Old Aug 8th 2017, 10:41 AM   #2
Senior Member
 
Woody's Avatar
 
Join Date: Jun 2016
Location: England
Posts: 338
Yes But

How is the coefficient of rolling resistance expressed?
Would I be correct in guessing that this is a function of velocity?

What you want to get to is something in the "F=ma" line.
you have "a" (the deceleration), you need to determine "F"
which I suspect should be derivable from the coefficient of rolling resistance.
__________________
~\o/~
Woody is offline   Reply With Quote
Old Aug 8th 2017, 11:22 AM   #3
Pmb
Physics Team
 
Join Date: Apr 2009
Location: Boston's North Shore
Posts: 1,195
Originally Posted by j95 View Post
Is it possible to determine the mass of an object (i.e Bicycle) given the (Coefficient rolling resistance), (Initial Velocity) and the (Deceleration). Given that you are able to change the (Coefficient Rolling Resistance) and from this determine a new (Deceleration). Wind resistance and internal frictions are neglected. If so how?
Possible? Yes. Easy? No.
Pmb is offline   Reply With Quote
Old Aug 8th 2017, 12:50 PM   #4
j95
Junior Member
 
Join Date: Aug 2017
Posts: 3
well yes, but the trouble is that you also need the mass to do that. To find the mass we would need to know either the momentum or the friction. But all we have is the "time to stop" which is dependent on both momentum and friction (I would think equally).

So how to relate the time or (deceleration) to a force/momentum relation.

For some reason I feel a linear approximation is necessary somewhere, because mass and the (tire size, tire pressure etc.) coefficients stay the same.
j95 is offline   Reply With Quote
Old Aug 9th 2017, 07:10 AM   #5
Senior Member
 
Woody's Avatar
 
Join Date: Jun 2016
Location: England
Posts: 338
you indicate that you can change the coefficient of rolling resistance.
This should allow you to set up a simultaneous equations scenario
which will in turn allow you to solve a problem with more than one unknown.

The key to this is the precise definition of "coefficient of rolling resistance"

without knowing exactly what that means, I can't advise further.
__________________
~\o/~
Woody is offline   Reply With Quote
Old Aug 9th 2017, 08:10 AM   #6
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Naperville, IL USA
Posts: 2,271
Rolling resistance is typically modelled as being equal to the coefficient of the rolling resistance (which is a constant) times the normal force. So mass cancels out:

$\displaystyle F = ma = -m \mu g$

So $\displaystyle a = -\mu g$

As for changing the value of mu: I suppose you could deflate the tires to increase mu, but all that will do is shorten the time to decelerate to zero - it still doesn't help with determining the value for m.
ChipB is offline   Reply With Quote
Old Aug 9th 2017, 08:36 PM   #7
j95
Junior Member
 
Join Date: Aug 2017
Posts: 3
Originally Posted by Woody View Post
you indicate that you can change the coefficient of rolling resistance.
This should allow you to set up a simultaneous equations scenario
which will in turn allow you to solve a problem with more than one unknown.

The key to this is the precise definition of "coefficient of rolling resistance"

without knowing exactly what that means, I can't advise further.
Coefficient rolling "friction" (u) i suppose, would be the unit-less number in this case. Which I am able to find out, and change by moving to gravel or another higher coefficient.

The work done during the coasting would be is W=(m)(g)(u)(d)
Then the Impulse Momentum (change in momentum) would be Jn = (Fnet)(t) = m(Vi-Vf)

and obviously W = Fnet(d)
The work and Impulse would have to equal out in some way because they're the only two forces acting on the horizontal.
j95 is offline   Reply With Quote
Reply

  Physics Help Forum > College/University Physics Help > Advanced Mechanics

Tags
determining, mass, momentum



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Momentum and changing mass jackthehat Kinematics and Dynamics 4 Nov 18th 2016 12:03 AM
Center of Mass and Linear Momentum googlefriend Kinematics and Dynamics 1 Oct 27th 2010 01:27 AM
[SOLVED] Particle of mass m has momentum of magnitude mc olyviab Quantum Physics 1 Apr 1st 2010 06:54 PM
Stuck on a similar problem - Determining the largest mass that the plate can hold jddery General Physics 0 Jan 31st 2010 08:39 PM
Determining equations werehk General Physics 1 Jul 29th 2008 07:39 AM


Facebook Twitter Google+ RSS Feed