View Poll Results: What will happen to the car
It will stay still (not move one bit) 8 17.39%
It will move forward 3 6.52%
It will move backward due to drag alone 5 10.87%
It will move backward even if there was no bearing drag or tyre drag 30 65.22%
Voters: 46. You may not vote on this poll

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Feb 25, 2009, 04:51 PM
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Poll

Inertia


What is it. can it be created or destroyed. is it always present or only sometimes.

I have a Hypothetical Question.

here it is Quick an Simple.

We have a car with the bearings degreased and completely free of any imperfections such as bumps or imperfect roller bearings etc etc.

We have disconnected any drive train portions.

We have the wheels of that car that are Perfectly balanced.

and the Tyres are just as perfect.

all up these items are so perfect that a small drop of water on one side of Top dead Centre of any one wheel would cause the wheel to rotate back and forth for at least 100 repetitions as if that drop was on a swing (When the wheel bearing axel system was suspended off the ground).

The Tyre is inflated to be hard as rock and is the hardest compound possible.

The wheels tyres car etc have normal mass. (that is they are not Assumed to have 0 mass)

We set the cars Wheel alignment as perfect as science can set it.

and now we set it on a treadmill which has a perfectly flat surface (Could be a sheet of Steel for all similarities for flatness)

NOW!

What we are going to do is Start the belt and Accelerate the belt from 0mph to 200mph within 3 seconds while the car is sitting freely on top. (Belt direction is backwards car face forward, speedometer reads +mph not -mph ) after three seconds the Experiment is over and all data collected.

For the purpose of the Example we will assume two more things.

1/ the tyre itself is as hard as steel (To eliminate friction within the tyre causing drag)

2/ the Tyre and Treadmill traction is flawless. IE you could accelerate from 0mph to 200mph in 1/100th of a second and the tyre treadmill would still have not slipped. (Just let it be that way)


OK

Here is the Question.

What will happen to the car? (will it move during those three seconds? and which way?) <relative to the Ground. Not relative to the treadmill surface.

Start Thinking
Last edited by Bryce.R; Feb 25, 2009 at 05:05 PM. Reason: Confirm wheels and car have normal mass
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Feb 25, 2009, 04:56 PM
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We assume the wheels to have no mass?
Feb 25, 2009, 04:58 PM
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willhaney's Avatar
I am presuming the wheels, having "Tyre is inflated to be hard as rock", have some mass.
Feb 25, 2009, 05:02 PM
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Quote:
Originally Posted by Brandano
We assume the wheels to have no mass?
thatís the second person to assume that or ask .

what part of the question lead to that assumption ?

For now I will add an extra portion stating that all mass is un changed Ie the wheels and car are of normal mass and weight.

Bryce.
Feb 25, 2009, 05:03 PM
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Then I know how to cast my vote.
Feb 25, 2009, 05:15 PM
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willhaney's Avatar
The car will move backward from the same forces that keep this lane from taking off:

Poll Something to think about.....Will it Fly? II
Last edited by willhaney; Feb 25, 2009 at 05:39 PM. Reason: fixed the link
Feb 25, 2009, 05:18 PM
Registered User
If there is no friction on the wheels, there is nothing to cause them to spin.

We can basically take the car out of the equation and talk about the wheels only.

I think I might want to change my vote.
Feb 25, 2009, 05:30 PM
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Take a belt sander and invert it so that the sand paper faces up and is parallel to the earths surface.

Place a rubber ball in the center of the sand paper.

Fire up the sander.

The accelerating belt produces a force on the ball.

This force does two things to the ball. It spins the ball and pushes the ball in the direction of the belt.

How mush it spins the ball and how much it pushes the ball is a function of the belts acceleration, mass of the ball and the distribution of the mass within the ball.

Will
Feb 25, 2009, 05:35 PM
Registered User
and the inertia of the ball, that's why I asked if the wheels have mass. the ball will try to stay still, but has a force applied to it, tangential to its lower side. Assuming ideal conditions the point furthest away from the sandbelt will keep static, so the center will move along the sandbelt at half the speed of the sandbelt. In the car example is a bit more complex, since there's the additional mass of the car body to account for, so the wheels will move at a smaller fraction of speed than half the speed of the treadmill. Now, if the wheels had no mass, the car would just stand still.
Feb 25, 2009, 05:37 PM
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yep
Feb 25, 2009, 05:42 PM
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Quote:
Originally Posted by bwalt822
If there is no friction on the wheels, there is nothing to cause them to spin.

We can basically take the car out of the equation and talk about the wheels only.

I think I might want to change my vote.
2/ the Tyre and Treadmill traction is flawless. IE you could accelerate from 0mph to 200mph in 1/100th of a second and the tyre treadmill would still have not slipped. (Just let it be that way)
Feb 25, 2009, 05:49 PM
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Is it bad forum etiquette to post a link to this thread within another sub forum on RCGroups ? (I know it would be bad in any forum to post the whole question and poll in another sub forum on the same Forum, but some forums allow the posting of a link if one feels the Audience level is low in Specific sub forums where said question belongs)

Bring more into the Fray. not everyone looks down here

Bryce
Feb 25, 2009, 06:01 PM
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Rules

[table 1 1 1]
Cross-posting|Posting the same content in multiple posts. Note that the moderators may take other actions rather than issue a warning, depending on the circumstance. They may choose to merge cross-posted threads, send cross-posted threads to the Bit Bucket, or take no action
[/table]

Technically, if the owner of the thread posts a link in another forum it is considered Cross-posting and has/does garner warning points and the post removed (hidden).

However, unless someone reports it, which doesnít happen often, itís acceptable and understandable.

Hope that helps,
Will
Feb 25, 2009, 06:09 PM
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Fingers crossed they will understand my reason for trying to reach a larger audience.

I will not post anything other than a link. that will make it less of a hassle in any case.

Bryce.

PS. I hope they go easy on me i mean I will not be posting the same content after all )

Gosh I hope they understand
Feb 25, 2009, 06:18 PM
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Chikened out :(


I couldn't do it, I chickened out
I thought of all those people talking happily in there individual sub forums and thought, na , this is not fair to them.

Also , there are so many sub forums. I would surly get the boot If I hit just 1/4 of them.

I think it would be best if we leave it be. or wait for word of mouth.

So if you all have some friends here on RCGroups.com then just send a link in a PM for me (I know no one here ) then they may pass it on to one or two of their friend and so on ?

Chicken
Bryce.


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