Tip the can

Greezer · Post by **Greezer** » Thu Dec 25, 2008 4:56 pm

Civilization, modern, is as crazy as it's ever been. I doubt there's anything truly civilized about man. I think though, it seems, there is a dumbing down effect happening due to the domestication process. Are there still metal detectors at the entry gates to those gated communities in your civilized location?

David Redszus · Post by **David Redszus** » Sun Dec 28, 2008 11:50 pm

Greezer wrote:Civilization, modern, is as crazy as it's ever been. I doubt there's anything truly civilized about man. I think though, it seems, there is a dumbing down effect happening due to the domestication process. Are there still metal detectors at the entry gates to those gated communities in your civilized location?

Not only do our gated communities have metal detectors but they come equipped with armed guards and attack dogs.

It reminds me very much of the Salt castle in Saltzburg Austria. An impenetrable fortress (equipped with a state of the art torture chamber) was built high above the river for protection.
Protection from rogues and thieves? From invading armies? From assasins and murderers?

No, no, and no. It was built to protect the local royalty from their own townspeople. Including the torture chamber.

Today we no longer tolerate such things. We have airport and bus terminal security. We have metal detectors at the Court House and at City Hall. Our local royalty ride in bullet proof limosines with armed guards.

Such is the nature of civilization.

plovett · Post by **plovett** » Fri Jan 30, 2009 5:48 pm

I think it's going to depend on the coefficient of friction between the can and the surface it's on. It will rotate if there's enough friction and enough acceleration.

paulie

David Redszus · Post by **David Redszus** » Sun Feb 08, 2009 3:58 pm

OK, so what does the coefficient of friction need to be?

plovett · Post by **plovett** » Sun Feb 08, 2009 4:37 pm

Shoot. Now I gotta figure out what the surface area is of the contact patch between a round 12 oz can on its side and the dashboard. Thanks lot!

paulie

MadBill · Post by **MadBill** » Sun Feb 08, 2009 5:13 pm

Ah, but for simple/classic cases, friction force is not dependent on contact area, just on normal force and friction coefficient...

plovett · Post by **plovett** » Sun Feb 08, 2009 5:16 pm

ah, that helps a lot.

What does a full 12 oz. can weigh?

paulie

MadBill · Post by **MadBill** » Sun Feb 08, 2009 5:37 pm

Should be right around 13 oz. weight, but per above, you don't actually need the weight either, as the friction force is directly proportional to it. All you really need (assuming the can is completely full) is the can dimensions.

jdavis · Post by **jdavis** » Sun Feb 22, 2009 11:42 pm

Also depends on which friction coefficient you're talking about. Yes there is more than one and DOZENS of ways to model friction beyond that

. Just thought i'd come in and muddy up the waters some more.

David Redszus · Post by **David Redszus** » Tue Feb 24, 2009 9:26 pm

Since the can is initially stationary, it would seem that the static coefficient of friction should be used.

Now you probably want to know the properties of the aluminum can and the plastic surface of the dash.

Picky, picky, picky.

jdavis · Post by **jdavis** » Wed Feb 25, 2009 12:43 am

Yeah well, many years and countless tax dollars later (thanks fellas, I kid but no really) I have learned to be picky.

Coefficient of static friction tisk tisk David you are thinking small. What if I want to model it on an infinitely large dash so she has room to slide around, and then decide to model the little bit of gas at the top that allows it to make that cool sloshing sound then I make a matrix of springs and dampers to predict the fluids response to excitation and the resulting reactions and the deformations of the can due to material properties and stress. Then what of the wind drag created as it moves along this dash and it falls over eventually due to its velocity rather than acceleration GASP (drag is related to velocity in an exponential fashion). Besides David if theres a little hop at the start maybe the normal force gets low enough it starts to slide along the dash

. Man that sounds like stuff I tell underclassmen to get them all crossed up when they ask me for help with thermo or heat transfer homework when I am busy

.

David Redszus · Post by **David Redszus** » Thu Feb 26, 2009 3:15 am

What if I want to model it on an infinitely large dash so she has room to slide around,

When you is slidin you ain't tippin. More Gs please.

Besides David if theres a little hop at the start maybe the normal force gets low enough it starts to slide along the dash.

Now you are incorporating Z axis G forces due to instability. If you keep that up, you will have to accept the fact that in the real world of engineering, simple, static values do not exist. Every measurement consists of inconsistencies and variations and we will have to evaluate transient data spikes and their relevance.

And don't forget about significant decimal places as you take those very fine data measurements.

Take that Mr. Heisenberg and stuff it.

jdavis · Post by **jdavis** » Thu Feb 26, 2009 12:17 pm

I know all about the static values not existing. I am always highly amused when people accept the book values as carved in stone for anything. Even our precious gravity if not set but we pretend it is, a little bit of work with a properly configured pendulum in a vacuum and some high buck sensors will tell you that. Most people come to realize that the book theory is a bunch of bs after seeing some strength of materials tests, or to a lesser degree in fluid mechanics lab. As engineers we are very happy if our answer is within 10% of the real world (25-30% if you work in heat transfer or fluid mechanics).

David Redszus · Post by **David Redszus** » Thu Feb 26, 2009 11:27 pm

OK, putting all the technical esoterics aside, can we agree on a simple equation that will approximate the G forces necessary to tip the can (assuming a static Mu value of 1.0).

jdavis · Post by **jdavis** » Fri Feb 27, 2009 9:28 am

We already did, when I posted the answer in post 3 of this thread. Its just a simple algebra and sum of the moments problem.

Now I pose a queston of my own. Assuming the acceleration(force) required to tip the can is constant at 1% more than static equilibruim how long does it take the can to fall flat on the dash and to stand back up. Assuming G = 9.81 and the mass of the can is 13oz. Extra points if you can provide a graph position vs time along with velocity and acceleration.