Car Quiz

[RWebb]

OK, let's see how you do -- if you know the source please don't post it for a few days.

1. If you hold your hand out the window while riding in a car (carefully!), you feel more drag if you hold your hand perpendicular to the ground compared to parallel to the ground. Why?

2. In Nascar’s “old car” — the one used before the Car of Tomorrow being introduced this season at Daytona — the fenders on the left-hand side of the car were much broader than on the right-hand side of the car. If the air on both sides of the car had the same pressure, what would the advantage be of having broader fenders?

3. When you place a tire pressure gauge on your tire and measure a number like 30 psi, that’s not the actual air pressure in your tire. What is the actual air pressure in your tire?

4. The temperature of the water in your radiator can actually get above 212 degrees Fahrenheit. Normally, water boils at 212 degrees, so how can this happen?

5. How much does the air inside the Unisphere weigh? The Unisphere is a model of the Earth made of a grid of stainless steel tubes, open to the air, with continents in solid stainless; diameter of the sphere itself is 120 feet, or 36.57 meters.

[sketchers356]

As a physicist I hope that everyone can answer all of these questions. There will be a quiz tomorrow.

[CJFusco]

1) because there is less frontal area to disrupt the air if you hold your hand parallel to the road.
2) NASCARs only had to turn in one direction.
3) psi= pounds per square inch. the actual pressure would be psi times square inches.
4) Coolant.
5) i don't think there is enough information to answer this question.

[island911]

Originally Posted by RWebb

...
3. When you place a tire pressure gauge on your tire and measure a number like 30 psi, that’s not the actual air pressure in your tire. What is the actual air pressure in your tire?...

do you mean to ask "total pressure" rather than "actual" pressure? . ...or are you thinking to subtract the partial pressure of the tire 'stink' inside the tire (which isn't pressure due to "air") ?

... because "actual [gauge] air pressure in your tire" is still "actual air pressure in your tire" and is more easily known than total pressure (where you would have to know temp, altitude...)

[Tobra]

your hand pushes harder for the same reason a 911 will tend to get light in the back if you have no wing and try to go too fast, iti s because of the way the wind hits it

the rad gets hotter because it is pressurized, water can get pretty hot before it boils if the pressure is high enough, also why stuff takes so long to cook in the moutains, lower atmospheric pressure gives lower boiling temp. The coolant gives higher boiling point for other reasons.

not familiar with a "Unisphere" can I put it in my pocket?

[island911]

"Unisphere" !?! . ..in your unitard ?

[Brian Cameron]

1. darn good question, guessing it is the airflow past the side of the car creating a vacuum (venturi effect) that pulls air toward the car across the perpendicular; vacuum has less effect (drag) on hand when hand is parallel to ground.

2. venturi effect of wider left fender tends to pull car to the left (sort of like a vertical wing)?

3. Assuming you're at sea level, ambient pressure approx = 14.7 psi + 30ps measured = 44.7 psi total. The actual answer depends on ambient air pressure where you're measuring, reductio ad absurdem, if you're in a zero air presure environment (eg space) the tire pressure as measured would actually be 30psi. Leaving aside partial pressure due to volatile hydrocarbons etc in the tire "stink" as noted by Island.

4. Tobra's right, coolant system is pressurized therefore water remains in liquid phase at higher temperatures.

5. 65,838.43 lbs, give or take, assuming dry air at 25C, 100Kpa, and disregarding the volume of the stainless steel tubes that look like little "orbit rings" outside the globe part of the sphere.

[tiwebber]

1. if I hold my hand perpendicular to the floor and move it quickly through the air horizontally to the floor, a leaf in front of the path of my hand moves. If my hand is parallel to the floor and I move it the same way, the leaf doesn't move (much). Answer - must be displacing more air -> more drag.

3. I agree with Brian but suspect there may be another source of pressure. If you put air in a balloon and then step on it, it will pop - it can only take so much pressure. I think that in addition to ambient air pressure, the weight of the car over the tire will add some more pressure so the "actual" pressure in the tire as measured by a guage will be less.

5. volume of the sphere is 904778 ish cubic feet and a cubic foot of air weighs 0.075 lbs (at sea level which is fair here) -> 67858 lbs

[onewhippedpuppy]

1. Dynamic pressure increases with velocity, and force from pressure = Pressure * Area. Your hand perpendicular to the ground has more surface area than when parallel, so more force is experienced.

2. NASCAR sucks. Cars only go left, so more frontal surface area on the left side would tend to yaw the car, increasing it's tendacy to turn left.

3. The tire gauge measures the difference between the ambient (atmospheric) pressure and the air pressure inside the tire. True pressure is the pressure inside the tire + ambient pressure.

4. Anti-freeze raises the boiling point of the water.

5. No idea, I can't picture what is described. I would guess you find the volume, then multiply volume * air density to find the mass of the air. Since it asks how much the air "weighs", multiply mass * the force of gravity to find weight force.
3.

[Laneco]

Not a scientist so here's layman explanation...

1. The hand parallel pierces the wind (less frontal area?) than the hand perpendicular (more frontal area - more drag)

2. More frontal area on the left would mean more downforce on that side to help "pin" the left side while the car turning to the left tries to throw the weight to the outside.

3. The pressure you are measuring is is failing to factor the air pressure already present outside of the tire in the atmosphere. But as most of us need to keep things pretty simple when adjusting tires, we just go off the guage instead of factoring the atmospheric pressure. Probably does make a difference though if you are racing at high altitudes.

4. Anti-freeze raises the boiling point of water and the pressurized system also changes the boil point.

5. Duhh.... What's a unisphere?

angela

[Jims5543]

1. Parallel
2. +1 for Brian's answer.
3. You must subtract atmosphere from the reading for true pressure.
4. System is pressurized
5. Zero

[Sapporo Guy]

Ok, I'm game.
Didn't google

1. Surface area difference. Think airplane wings. also, just a small tidbit ... if you drive at about 60mph you'll get the impression that you're feeling ... ..... err ... bouncing jello !!!

2. "broader fenders?" height or width? If height, I'm gonna agree with the left turn fact and add in that if the suspension is also higher on the same side, then probably stability in turns is added.

3. "30 psi" --- I forfeit this answer. I didn't want to cheat by going to google.

4. +1 pressurized (not much but enough) +1 coolant.

5. lolo, a bit more than zero ... once again google has the answer



Actually, I should just erase my answers and give you Henry Ford's answers. "hold on while I call my bean counters " That was probably one of the most educated answers I have read!

[Porsche-O-Phile]

No, if the conveyor belt speeds up the plane still won't get airborne unless it moves relative to the air (not the ground).

[tiwebber]

I want my test results.

[rouxroux]

Originally Posted by tiwebber

I want my test results.

They came back negative. Just be a little more careful nest time.

[WI wide body]

[QUOTE=RWebb;3765004]OK, let's see how you do -- if you know the source please don't post it for a few days.

1. Depends if you are traveling the same direction that the earth is rotating.

2. Broader fenders allows NASCAR more advertising stickers.

3. If you place the gauge on top of the tire it will always be zero.

4. Excess alcohol content causes various and sometimes illegal maladies.

5. Info is incomplete. Continence is good for teens but not so good for tubes. Air on the other hand is often vapid but seldom sempiternal. I think.

[Joeaksa]

You guys have far too much time on your hands!

[Brian Cameron]

Answers here:

http://tierneylab.blogs.nytimes.com/2008/02/22/nascar-riddles-solved/

[masraum]

Originally Posted by Sapporo Guy

4. +1 pressurized (not much but enough)

Huh? It's actually pressurized by over an atmosphere. Most radiator caps pressurize a system to 16PSI. That's above the 14.7 that's already atmospheric pressure. To get the same pressure by swimming down underwater, you'd have to go over 10 meters to probably about 35'. I think the extra pressure raises the boiling point by over 35* F (up to about 250*)

[Dantilla]

Experiment 1:

Went for a drive, with my wife's hand parallel to the ground, my hand perpendicular. Results:

Wife's hand had less drag. Must be because her hands are smaller.

Experiment 2:

Sorry, I'm having a hard time renting a car from a Nascar team. I'll get back to you after Roger Penske returns my call.

Experiment 3:

I thought the most accurate way was to see the actual pressure for myself. I dismounted the tire from the wheel, and looked inside. Results:

Inconclusive.

Experiment 4:

You're lying. Once again, searching for valuable first-hand information, I removed the radiator cap to measure the tempurature. IT WAS BOILING!! Results:

Ouch!

Experiment 5:

Okay, enough first-hand experiments, so here's a guess:

A banana.