Riddle Me This Batman.....

[VEETENN]

You see a Viper GTS traveling down the road. The GTS is completely stock (gear ratios, engine, tires & wheels etc. "1998"). You have a type of radar that allows you to clock the speed of the Top Dead Center of one of the rear tires. The speed of TDC of the tire is 70mph.

What is the speed of the Bottom Dead Center of that same tire?

 

[Bill Pemberton Woodhouse]

**** , I almost had the answer and then I realized I didn't know if the car was going East,West, North or South, and the tires could have been Pilot Sports at 18" , or MXX3's at 17". Hmmm, since you are in California, why not bring out some of Napa Valley's finest and I'll grab the Omaha steaks and we will sit around the charcoaler and ponder................

 

[treynor]

The speed at bottom dead center is, of course, zero unless he's spinning his tires. Assuming the speed of the TDC is specified relative to the road and direction of travel, the car is traveling 35MPH regardless of wheel size.

*has a sneaking suspicion this is too simple to be the right answer*
Ben

 

[Performin Norman]

Treynor is right on target. If the top of the tire is going in a vector of 70mph, how fast is the center of the wheel going? What is the rotational velocity of the wheel?

 

[Doug Supercharged Vipers]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 'Mark O':
If Jesus was Jewish, how come he has a Puerto Rican name?

<HR></BLOCKQUOTE>Because he ate black beans and rice for his Last Supper. And yes, it was the Early Bird Special!

Doug

 

[Doug Supercharged Vipers]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
What is the speed of the Bottom Dead Center of that same tire?

<HR></BLOCKQUOTE>The same as the top, 70 mph.

Regards,
Doug

 

[shawalka]

0 mph.....learned this in physics just this past semester. THe top of the wheel is going at 70mph, the center of the wheel (and the speed of the car) would be 35mph, and the bottom of the wheel where it contacts the road is 0mph. Doug, the bottom of the wheel would be travelling at 70mph only if the wheel was mounted on an axis through the center of the wheel. In this case, the wheel is rotating along the ground, and the speed is not the same top and bottom, because point of rotation is not the same distance from the axis of rotation (top and bottom). You guys know Vipers, and how to drive fast cars....I admire that, and wish to do that one day, but for now, I'll just be happy knowing physics

Happy Vipering.

 

[treynor]

On Doug's car, the bottom of the tire probably does move at 70 MPH on a regular basis

. For the rest of us mere mortals, the bottom of the tire is usually in static (albeit rolling) contact with terra firma, which means it's moving at zero MPH.

 

[VEETENN]

Those who answered 0-mph are CORRECT! Not being a math or physics expert I have to explain in terms I understand. It is easiest to visualize if you think of the track on a bulldozer. As you watch the bulldozer move(forward) you will see the track move across the top down around the front track wheel and then the track plants itself on the ground (dead stop) forcing the bulldozer to move forward until the track picks itself up around the back track wheel and starts the cycle again.

 

[TOOOFST]

Thanks Mr.Brad/fan.I was hoping to learn something today!Answer this ?Why does it hurt when I ***.

 

[kverges]

yes, but what is the air speed velocity of an African Swallow?

 

[silverviper]

Well, maybe not exactly. Doesn't the tire deform slightly as it contacts the road surface? Something about coefficients of elasticity and a slight frictional resistance to rolling? I'd guess that the speed of the tire at the point of contact is exactly zero only in a massless, frictionless ideal physics problem type of world. Or maybe I'm wrong.

Cheers.

 

[brett]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by kverges:
yes, but what is the air speed velocity of an African Swallow?

<HR></BLOCKQUOTE>

Laden or unladen?

By the way: Although the answer is "physically" correct (good riddle)if there are some assumptions made. The question was flawed in the fact that it didn't ask for the tires speed in relation to its contact patch (the ground). In physics you don't just assume that's implied...

 

[Paul Hawker]

If the speed of the tire at the road surface is zero, how can it propel the viper forwards at 35 mph (the speed of the hub)?
As a side note according to John Force. His funny car is still spinning it's wheels going thru the traps at + 300 mph!

 

[shawalka]

Whether the tire stretches a little or not will not make it have speed. Whether it is stretched or in equilibrium, the tire is contacting the road and not moving. The very bottom point is the only point without speed. If you move a fraction of an inch around the wheel in either direction, the tire will once again have a speed. In regards to the polishing wheel, try taking the polisher, and letting it roll along the ground at 70mph (assuming that is the speed of the rotation of the disc). The disc will travel along the ground (assuming its balanced and doesn't fall over ) at 35mph, and NOTHING will get polished. My last post was a little unclear. The tire is rotating along an axis through the center of the wheel, but we are examining an object which is in translational movement (going forward with the car for those who need clarification....not saying that anyone here really needs it). Thus....well...its really hard to put this in words....but....the bottom is at 0mph...hehe, have a good one guys. BTW, happy 4th of July! Fire up those BBQ's!

How about this for a brain tickler? If you rolled a Viper rim and tire (mounted of course) down a hill, and rolled just a Viper tire without rim down the same hill, releasing them both at the same time, which would reach the bottom first? It's the summer, and I feel like I'm back in school already....see what you guys did to me?! Good luck!

 

[shawalka]

Just saw the last post....The Viper is propelled forward because there is a horizontal force being applied to the bottom of the wheel. The wheel isn't moving at the bottom though, because the force of friction from the tire to the ground is greater than this force of acceleration of the car. Hence, is the acceleration force becomes greater than the force of friction, the tire begins to spin, and we all know how fast a car will accelerate when the tires are just spinning relentlessly. As long as the friction force is stronger than the acceleration of the car, the car will go forward. Hence, drage slicks let you launch better, by increasing the amount of frictional force of the tire. And, as a little strategy, the 'perfect' drag lauch would be one where the acceleration of the car (how far you mash the gas, slip the clutch) is just slightly less than the force of friction of the tires. This would make the most forward acceleration. Now, if I only had a Viper to try this in...hehe...my time will come....

 

[brett]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by shawalka:
How about this for a brain tickler? If you rolled a Viper rim and tire (mounted of course) down a hill, and rolled just a Viper tire without rim down the same hill, releasing them both at the same time, which would reach the bottom first? It's the summer, and I feel like I'm back in school already....see what you guys did to me?! Good luck!

<HR></BLOCKQUOTE>

This has something to do with gravity huh?

In perfect conditions (vacuum, terrain is smooth, etc.) it's a tie!

It's summer already? Don't you have something better to do?

Like Chicks, and I don't know....stuff?

 

[treynor]

&gt; In perfect conditions (vacuum, terrain is smooth, etc.) it's a tie!

Actually, it's not a tie. The wheel+tire combination has a different ratio of rotational inertia to mass than the tire alone. Since to roll down the hill you will have to convert potential energy into both kinetic and rotational energy, the ratio matters, and thus one or the other will be first.

A moment here, while I work this one out...

 

[Paul Hawker]

If I have 17" tires on the front, and 18's in the rear, which tire will be going the fastest.

Hi Brett. That chick thing sounds like a great idea....how's the dogs?

 

[treynor]

OK, I believe the wheel + tire will reach the bottom first. The general case is more than I really feel like tackling this late in the day (for both shapes, calculate rotational inertia by integrating the function of mass as a distance from center by the distance * 2 * pi, then calculate V as a function of MH by relating Ik to Ir, etc. etc.), but in layman's terms, since the wheel is a smaller radius than the tire, it will contribute less to rotational inertia regardless of its weight or shape, and thus a larger fraction of the potential energy the wheel adds due to its mass will convert to kinetic energy, and thus the wheel + tire combo will arrive at the bottom of the hill moving faster (and thus first).

 

[brett]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by treynor:
&gt; In perfect conditions (vacuum, terrain is smooth, etc.) it's a tie!

Actually, it's not a tie. The wheel+tire combination has a different ratio of rotational inertia to mass than the tire alone. Since to roll down the hill you will have to convert potential energy into both kinetic and rotational energy, the ratio matters, and thus one or the other will be first.

A moment here, while I work this one out...

<HR></BLOCKQUOTE>


I don't think it comes into play, but if it does you may want to take into consideration the length of the race.

I think in your scenario one of the tires will convert its energy at a faster rate thus making it quicker, but potentially have the least energy as the "experiment/race" continues. (slower)

 

[shawalka]

Ben, you are indeed a smart man. The wheel+tire combination will reach the bottom of the hill first, regardless of the length of the hill. The key factor here is the inertia of the center of momentum. A hoop (just a tire) has an inertia of mass X radius^2......a cylinder (wheel and tire) has inertia of 1/2 mass X radius^2. What will happen in this 'race,' is that the wheel and tire together will accelerate faster than the tire alone. Although all things fall at the same rate (with similar air resistance), when an object is rolling, much of the energy in the system must be converted to rotational energy (spinning) as well as translational energy (going down the hill). In this case, the wheel+tire combination takes less energy to spin than the tire. Think of it this way. The more mass that is near the center of rotation, the easier it is for something to spin. Smaller rims are easier to turn that large rims. If you spin in your office chair really fast with your arms out, and then pull them in, you will spin faster. The more mass that is near the axis of rotation, the easier it will spin, and the tire itself has its mass a distance from the center. The tire and wheel combination has mass closer to the axis. Cheers to Ben for being on the ball with all this physics trivia. Everyone have a good morning/day/night, depending on when you read this.

 

[shawalka]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR> In perfect conditions (vacuum, terrain is smooth, etc.) it's a tie! <HR></BLOCKQUOTE>

Well, after looking at that explanation, you are correct. Assuming you are in a vacuum (no air resistance), and the terrain is smooth (smooth being defined as frictionless), then both objects would merely SLIDE down the hill, not spinning at all, and Galileo's principles would apply, and each object would reach the bottom at the same time. But, under more 'normal' conditions, Ben has the right idea.

Brett...Yes, I have other things to do. Chicks have been quite a pain lately (like they ever aren't). Last girl I went out with tells me she's bisexual and she gets all freaky. Maybe most guys like that, I'm more of a simple guy. Working 40 hours a week, doing work around the house, and going out at night occupies my time, however, today has been slow, and I'm just passing time with all you fine Viper owners. You can't really blame me for trying to keep my mind sharp can you? After all, aren't all my elders supposed to be teaching me to do well in school, and stay away from trouble? Hehe...I think I'm doing fine. If I had a Viper, I'd be out cruising or at Englishtown making a few passes...don't you have 'stuff' to do?

 

[PMUM]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by shawalka:
Chicks have been quite a pain lately (like they ever aren't). Last girl I went out with tells me she's bisexual and she gets all freaky.

<HR></BLOCKQUOTE>

Poor guy. That really *****. BTW, what's her number?

 

[Doug Supercharged Vipers]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by brett:
Laden or unladen?

By the way: Although the answer is "physically" correct (good riddle)if there are some assumptions made. The question was flawed in the fact that it didn't ask for the tires speed in relation to its contact patch (the ground). In physics you don't just assume that's implied...

<HR></BLOCKQUOTE>&gt;&gt;The question was flawed in the fact that it didn't ask for the tires speed in relation to its contact patch (the ground). &gt;&gt;

Exactly my point!!

I took Big Red out today for an educational spin and it was exactly what I said, the rear tires were the same speed both top and bottom

.

Regards,
Doug

 

[brett]

I was with ya' Doug.

But, now I'm trying to figure out how the "slide rule" computation was accomplished to "rule out" the Bi-******?**

Was she a spinner?

She threw you a curve?

Well....then we could discuss Bernoulli's principle couldn't we?


**edited for the moderators

 

[brett]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Paul Hawker:
If I have 17" tires on the front, and 18's in the rear, which tire will be going the fastest.

Hi Brett. That chick thing sounds like a great idea....how's the dogs?

<HR></BLOCKQUOTE>


You can't have different sized tires on your car Paul. You're on your way to certain peril. The 18" tire on the rear will turn faster than the fronts because everybody knows (for both shapes, calculate rotational inertia by integrating the function of mass as a distance from center by the distance * 2 * pi, then calculate V as a function of MH by relating Ik to Ir, etc. etc.), but in layman's terms, since the wheel is a smaller radius than the tire, it will contribute less to rotational inertia *** blah blah blah....

The front of your car is going to go slower than the back of your car and the end result will be what motocross riders call an "endo", (end over end)therefore I sugesst before attempting a crazy stunt like two different sized tires (insane concept) you should revisit your Physics classes form College. Duh!

The Dogs are great thanks for asking...those other little things are fine too. Uhmmm...what are theyyyyyy...ooyy...the kids, yeah I knew I'd get it... Whew! All that "laws of Physics" stuff I had to recall from 18 ys ago just plumb wore me out!

***Treynor

By the way Treynor, not a slam just having fun with Paul.

 

[GTS Dean]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Brad/Viper-Fan:
It is easiest to visualize if you think of the track on a bulldozer. <HR></BLOCKQUOTE>

That's an explanation that I can relate to!

 

[Daffy]

So, if a cop traps my speed at 70 mph in a 55 mph zone, I can use this simple explanation to prove I was actually parked at the time, so no ticket, right!?!

Dave.

 

[Supercharged Vipermad]

Originally posted by 'Mark O':
Here's a couple other good questions to ponder.....

If Jesus was Jewish, how come he has a Puerto Rican name?

Does a one legged duck swim circles?

Mark? Whats the speed of Fart coming out of your butt?? Answer that butt man

)