For physics majors.... My friend was joking that my GS's top speed would be greater if it was dropped out of a plane than driven down the road. I didnt argue as ive only hit 115 mph, downhill....
Anyone know what the terminal velocity of a GS is from lets say 30,000'? I think objects fall at a constant rate of 9.8 meters/second cubed.
9.8 meters/second cubed is the acceleration of an object under gravity, not the velocity. This acceleration is reduced by wind resistance as speed increases. Eventually the force of the resistance will cancel out the force of gravity, and this is the point of terminal velocity. The amount of force that wind exerts on an object depends on the shape of the object...not sure what the terminal velocity of a GS500 would be.
Short answer is most likely if the wheels are pointed to the ground in the 'riding position'. Average terminal velocity for belly-down skydiver is approximately 120MPH. There is a complex formula on Wikipedia if you would like to figure it out exactly:
http://en.wikipedia.org/wiki/Terminal_velocity
Hmm. Could we assume it is a solid object and find the average frontal area of three of its faces? I assume it is tumbling as it is falling. Should not be very hard get an estimate in the ballpark.
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Anyone know the Drag Coefficeint of a GS500?
http://ecomodder.com/forum/emgarage.php?do=details&vehicleid=3573
This GS500 might fall faster :cookoo:
OK... I was bored at work, and I kind of missed high school physics, so I did some calculation.
Acceleration due to gravity: 9.81 m/s^2
Mass of a GS500 (dry): 169 kg
Density of Air (approximate): 1.225 kg/m^3
Drag Coefficient of a GS500: 0.75 ???
Area of a projected object gets a little tough if it's tumbling. Let's assume it's somewhere between the 3 orthagonal projections of the bike (front/back, side, top/bottom)
Wheelbase: 1.47345 m
Height: 1.045 m
Width: 0.745 m
So...conservatively assuming that the projection is the same as the projection of a box with these parameters, and then averaging the area of each side of the box you get:
Average Projected Area: 1.1 m^2
Putting it all together you get:
SQRT(
2 * 169 kg * 9.81 m/s^2
1.225 kg/m^3 * 0.75 * 1.10 m/s^2
) = 57.3 m/s or 128 mph
A lot of approximations there, but should be somewhat close to the right answer. :dunno_white:
I agree with your friend. The GS weighs about 380lbs without a rider. At it's maximum speed, the stock engine is putting significantly than 380lbs of force on the rear wheel. Assuming that the bike maintained an optimal aerodynamic profile while falling, gravity would pull harder than the engine.
In practice, the bike probably will tumble, so the comparison would be more difficult.
Don't most objects fall to a terminal velocity of 220 -260 kph? I stress most, I would love to see a feather not in a vacuum fall at 240 kph lol.
Quote from: burning1 on April 18, 2012, 02:14:20 PM
I agree with your friend. The GS weighs about 380lbs without a rider. At it's maximum speed, the stock engine is putting significantly than 380lbs of force on the rear wheel. Assuming that the bike maintained an optimal aerodynamic profile while falling, gravity would pull harder than the engine.
In practice, the bike probably will tumble, so the comparison would be more difficult.
What are you planning? Riding straight up a wall? On level ground, the weight only matters to acceleration. Maximum sustained velocity the engine has to overcome friction, like drag. It doesn't have to "lift" any weight at all, so heavy or light, two bikes with the same frontal area & frictional drag will have the same max velocity.
I agree. Looks like the back-of-the-envelope calculation confirms falling is faster than riding. Cool. O0
math. i hated math. and this is a reminder why :flipoff: lol
Lol too right
Quote from: 5thAve on April 18, 2012, 04:03:23 PMI agree. Looks like the back-of-the-envelope calculation confirms falling is faster than riding. Cool. O0
back of the envelope!? ... i mean cool that you wish to recycle and all but .. for matters as serious as this i beleive back of the beer mat is preferred!! :cheers:
math and physics are awesome though. realizing the complex things that you can figure out is astonishing. In high school (a small private and relatively exclusive school) My AP calculus and AP Physics teacher were one and the same. One day near the end of the year, in the weeks leading up to the AP exams, he gave us a single problem to solve one week. A coil of copper wire with 100 turns, a mass of 1 kg, and a diameter of 1 meter is dropped from an altitude of 10000 meters directly above earth's magnetic north pole, what would be the increase in length of the wire induced by the temperature change caused by the magnetically induced current in the coil as it fell. we were given all of the constants and parameters we needed, and over the course of that week, we figured it out. I don't think I could do it now... but that exercise was one of the most engaging things I've ever done in a classroom.
first, determine the function that describes the velocity of the coil
then, determine the magnetic flux per speed at altitude
then, determine current induced in the coil based on velocity, turns of the coil, area of the coil, and magnetic flux
then, determine the heat generated by that current
then, determine the increased length of the copper wire caused by that heat
oh wait, now our coil area has changed due to the wire being longer... so flux has changed... so current has changed
rinse, repeat.
being able to figure that kind of stuff out is why math is awesome.
gahhh, math hate all over again! :technical: :technical: sit me down in front of an engine with a nice set of tools and i'll put it together flawlessly, blindfolded, drinking beer with my wife nagging me hahaha. 6 beers left from a 12 pack, means i have 6 left. good to go! lol :cheers:
Quote from: bombsquad83 on April 18, 2012, 01:24:08 PM
http://ecomodder.com/forum/emgarage.php?do=details&vehicleid=3573
This GS500 might fall faster :cookoo:
WTF IS THAT?
Quote from: Roxtar on April 18, 2012, 07:00:36 PM
math and physics are awesome though. realizing the complex things that you can figure out is astonishing.
removed cos my brain hurt
being able to figure that kind of stuff out is why math is awesome.
i figured it out though ... the coil will hit the ground or water depending on where it was dropped ... but as i wasnt there to see it fall did it actually happen at all? :flipoff:
Terminal velocity combined with an abrupt stop is a real son of a gun. ( Can you say Buddha Loves You on here )
I once had a backup call to a tandem skydive fatality case in the redlands ( south of Miami ), complete failure of main, cut loose, and reserve never activated, both individuals hit belly down in perfect skydive form. They must have been completely paralyzed with fear and did nothing after releasing the main. The landing zone in that area was pretty much all solid coral rock----not at all a pretty sight. All bones shattered, avulsion of internal organs via the mouth ( and well---you know ) I wonder if knowing the combined body weight, you could determine the ft pounds of energy expended when they hit. I really couldn't handle much more than a fleeting glance, not so with the two homicide dets handling the case-----which reminds me of an old police inside joke; How can you tell the homicide boys on a death scene?----Ans; They are the only ones laughing.
Quote from: slipperymongoose on April 18, 2012, 03:12:59 PM
Don't most objects fall to a terminal velocity of 220 -260 kph? I stress most, I would love to see a feather not in a vacuum fall at 240 kph lol.
FIRST, it's not Cubed but Squared. 9.8 meters per second per second.
Moving on... Slips (and I am calling you this to avoid confusion with other readers otherwise it'd still be Mong :)) there is a video of a Hammer and a feather being dropped on the moon. No air to slow the feather. Both fall at the same rate. :thumb:
Michael
Yeah I've seen that trick at the science museum, but real world feather would take its sweet time compared to a hammer or a GS dropped from a great height.
Awesome replies! Thanks! So it appears a GS would fall faster than u can ride it, kinda figured.
Now if we could just get someone to try it. :D
Quote from: bombsquad83 on April 19, 2012, 06:00:49 AM
Now if we could just get someone to try it. :D
Im someone has a spare GS Ill ride it until about 6,000 ft :D Then Ill pull my chute and watch it fall haha.
Quote from: 5thAve on April 18, 2012, 04:03:23 PM
What are you planning? Riding straight up a wall? On level ground, the weight only matters to acceleration. Maximum sustained velocity the engine has to overcome friction, like drag. It doesn't have to "lift" any weight at all, so heavy or light, two bikes with the same frontal area & frictional drag will have the same max velocity.
I agree. Looks like the back-of-the-envelope calculation confirms falling is faster than riding. Cool. O0
Well, look at it this way... On the ground, the force of the engine at the rear wheel is being used to overcome the wind resistance of the bike. Falling, the weight of the vehicle is being used to overcome the wind resistance of the bike. If the force of the engine at max speed is greater than the weight of the bike, it will go faster on the ground than in the air. If not, the opposite is true*. I attempt to explain my logic...
* Again, assuming that the bike is falling perfectly nose-down.
This is not true because the weight of the bike has any bearing on max ground speed. It is true because the weight of the bike has a massive impact on falling speed.
Remember: Gravity applies a force to the motorcycle equal to the object's weight. The engine also applies a force to the motorcycle. At the engine, this force is measured in foot pounds. We can take the force, multiply it through the various gearing ratios of the transmission, and compare it to the rear wheel size to determine how many pounds of force the engine is actually applying to the rear wheel, at top speed. If the engine is applying 380lbs of force to the ground on a 380lb bike, the bike is capable of accelerating exactly as hard as gravity is capable of pulling the vehicle. The vehicle achieves exactly 1G forward force, but it is being met by exactly 1G of wind resistance, exactly as if the vehicle is falling perfectly nose-down.
Top speed is independent of acceleration, as you point out, and the weight of a vehicle isn't terribly important when trying to reach maximum speed on the ground. However, when falling, maximum speed is determined by the coefficient of drag to area vs the weight of the object. That's where the vehicle weight is important.
If you compare two objects with the same size/shape/etc, but different weight, the heavier object will always have a higher TV.
As a side note: It's very difficult to measure the Coefficent of Drag for a vehicle, or the forward area of a vehicle. But using the above information, it's actually possible to calculate the CdA of any vehicle that has a published dyno chart, gearing ratios, wheel sizes, and listed top speed.
great thread! loving it
Quote from: Twism86 on April 19, 2012, 05:51:26 AM
Awesome replies! Thanks! So it appears a GS would fall faster than u can ride it, kinda figured.
unless it's cbrfxr's bike 8)
BTW, from a previous thread, here's the driving force curve for a stock GS500.
(http://i261.photobucket.com/albums/ii63/ctbarbour/gs500-shift-chart-stock-1.jpg)
With most bikes, a wheelie occurs around 1G of acceleration... If you take the weight of a stock GS500, add a rider, gear, and gas, you see that even at peak torque in first gear, the bike probably doesn't have enough grunt to lift the wheel through throttle alone.