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-   -   Speed of Light? Chicken or the Egg? Physics fun. (http://www.wakeworld.com/forum/showthread.php?t=794904)

wakeboardingdad 08-04-2012 12:22 PM

Speed of Light? Chicken or the Egg? Physics fun.
 
As I rode my bike today on my 9 mile loop on the countryish roads around my house I looked down at my odo and contemplated the following:

On Father's Day 2010, my sons gave me the odo for my bike. My mountain bike. I calibrated it and checked it against my known 9 mile loop that I had checked with my car. It was close. After a hiatus of riding my bike, I finally switched from my knobs to my road tires for some summer time riding on the roads. They are smaller in diameter. Not much, but enough to cause the kickstand to be a little long and the bike to be a little tippy when on flat surfaces. The odo, on my proven 9 mile loop now reads 10.36 miles at the end. That's a pretty good jump.

So, my question is this (and don't just answer without some contemplation 'cause that's the fun part)

Is the energy expended for my good ole 9 mile ride just increase 15%? Because the driving system (wheels, chain, pedals, cranks, me) just rode reduced sized wheels which caused add'l revolutions, did I get a better work out without actually riding further (geographically)? Or did the reduced sized wheels, reducing the effort to rotate them, cause me to have a lesser workout? OR did the reduced diameter wheel assembly cause which takes more effort to travel over rocks, animals, bumps and edges, increase my workout? OR again, did I just time travel? :o

Kind of the like speed of light question that some were asked in school. For those who do not know it, here it is.

If you were in your car, traveling at the speed of light and you turned on your headlights, would?

a) your headlights extend in front of you, thusly at twice the speed of light?
b) your headlight filaments burn in two due to the immense heat because the light and heat are trapped in the headlight bulb?
c) your headlights shine brightly on your rear bumper?

:D

wake77 08-04-2012 1:13 PM

To your last question, I would answer d) none of the above. I know it is a hypothetical question, but only massless particles (photons) can travel at the speed of light. So if the car could approach the speed of light within hundredths of mph, light from the headlights would still be projected back to you from any object in your path of motion.

ralph 08-04-2012 1:36 PM

Quote:

Originally Posted by wakeboardingdad (Post 1773549)
Is the energy expended for my good ole 9 mile ride just increase 15%? Because the driving system (wheels, chain, pedals, cranks, me) just rode reduced sized wheels which caused add'l revolutions, did I get a better work out without actually riding further (geographically)? Or did the reduced sized wheels, reducing the effort to rotate them, cause me to have a lesser workout? OR did the reduced diameter wheel assembly cause which takes more effort to travel over rocks, animals, bumps and edges, increase my workout? OR again, did I just time travel? :o

How many times the wheels go round does not change how much work is done, you are not turning the wheels directly, you are turning the cranks.

What is important is the rolling resistance, the air resistance and the time taken. Without knowing if you rode faster or not it is impossible to say if you expended more energy or less.

wakeboardingdad 08-04-2012 2:01 PM

Jeremy, I bet you the kid in the neighborhood that told everyone that Santa wasn't real.

ralph 08-04-2012 7:01 PM

For the speed of light question IMO the correct answer is a variation of a. The head lights do extend in front of you because the speed of light is relative to the observer. Which is a paradox but the current understanding of light.

Shooter 08-05-2012 9:05 AM

As Ralph said, there are too many factors to judge overall effort beyond just the size of your wheels. It is a calibration issue and doesn't mean you rode any further or less. If you think of it in terms of gearing, the larger tires are probably slightly more energy efficient at higher speeds.

As far as the speed of light question..Factor in the theory of relativity into your question and you would be traveling back in time. How does that effect your view of light moving forward in time? Makes your head spin.

Shooter 08-05-2012 9:26 AM

Quote:

Originally Posted by wake77 (Post 1773559)
To your last question, I would answer d) none of the above. I know it is a hypothetical question, but only massless particles (photons) can travel at the speed of light. So if the car could approach the speed of light within hundredths of mph, light from the headlights would still be projected back to you from any object in your path of motion.

This may be wrong. Although not proven, a recent experiment showed that neutrinos moved faster that the speed of light. It is believed neutrinos have a very small amount of mass

http://www.mibba.com/Articles/Scienc...-Proven-Wrong/

fly135 08-05-2012 9:34 AM

I'd say that the main two factors in any change of energy output would be...

1) A change if any in the rolling resistance.
2) A change if any in the average RPM of your legs on the crank.

If neither of those changed, then there would be an increased loss (perhaps only slight) in the frictional components of the drive train that were moving faster because of the higher RPM at the wheel.

bigdtx 08-05-2012 10:20 AM

I was in a job interview and I opened a book and started reading. Then I said
to the guy, "Let me ask you a question. If you are in a spaceship that is
traveling at the speed of light, and you turn on the headlights, does anything
happen?" He said, "I don't know." I said, "I don't want your job."
-- Steven Wright

magic 08-05-2012 8:03 PM

Quote:

Originally Posted by fly135 (Post 1773637)
I'd say that the main two factors in any change of energy output would be...

1) A change if any in the rolling resistance.
2) A change if any in the average RPM of your legs on the crank.

If neither of those changed, then there would be an increased loss (perhaps only slight) in the frictional components of the drive train that were moving faster because of the higher RPM at the wheel.

The road tires are:
- Smaller
- Have less rolling resistance

Putting slicks on decrease the circumference of the wheel. Without calibrating the bike computer to account for the changed wheel size it would now be inaccurate. Bike tires use their inner measurement, so 700c wheels are really 622mm and the same as 29ers inner measurement. Their outer measurement will be different, heck even the same brand tire will be different in circumference between lots.

816 08-05-2012 8:20 PM

If you were traveling as fast as a speeding bullet and put a gun out the window pointed in the direction of travel
and pulled the trigger would the bullet just drop on the ground?

JoLo_Si 08-06-2012 1:18 PM

If the street tires are smaller they have to spin more times to reach the same distance of travel. However since each revolution of the wheel is that much shorter is will take that much less energy to turn them one complete turn. But then you get into torque vs rolling resitance, assuming you never change gears. More mass towards the center of rotation helps acceleration, when the mass is further from the center it helps to prolong the spin. So my thought is that the difference in energy expended on the same length ride with two different size tires is how many times you have to slow down and then accelerate assuming you never change gears to resist this effect.

It's a racin thang. Taller tires for longer tracks with wide turns, shorter tires for short tracks with tight turns that you need to accelerate out of.

fly135 08-06-2012 1:46 PM

Quote:

Originally Posted by ralph (Post 1773587)
For the speed of light question IMO the correct answer is a variation of a. The head lights do extend in front of you because the speed of light is relative to the observer. Which is a paradox but the current understanding of light.

The light would be sucked into your vehicle's black hole that resulted from it having infinite mass.


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