Scioly.org

_HenryHscioly_ wrote:for time, how can u determine the minimum time?
if 2.8 wud be "impossible" for 10m, what is the, fastest ideal time?

You can't really, meaningfully, at least not without a lot of complexity, and assumptions. You can start with the limiting physics of a falling body, falling 1m; terminal velocity would be about 3.1m/sec. There is no way to go any faster than that. So, in a very simplistic way, 3.1m/sec, calculate t for whatever distance, is the "ideal."- 6.2m in 2 sec, 9.3m in 3 sec, so around 3.5 to 10m
From that upper bound, deducts from that for center of mass falling less than 1m, for converting from straight down to horizontal, loss into rotational momentum spinning up the wheels (depends on radius and mass). Then, how rapidly your instantaneous velocity at the bottom of the ramp degrades- what do you assume, for rolling resistance, rolling friction, aerodynamic drag), for your "ideal"?

hmcginny wrote:

_HenryHscioly_ wrote:for time, how can u determine the minimum time?
if 2.8 wud be "impossible" for 10m, what is the, fastest ideal time?

There is nothing saying that 2.8 for 10m is actually impossible, it would just require so little friction that it seems nearly impossible. I wouldn't be that surprised if, by the end of the year, we see cars going that fast. Ideally, a car would be able to travel ~4.429 m/s, meaning a time of ~2.26 seconds for 10 m. However that assumes there is a perfect transfer of potential energy to kinetic energy, which very few ramps will offer, as well as a center of mass at exactly 1 m and absolutely no friction or air resistance or any other dissipative force. So the theoretical fastest time within these restrictions is 2.26 seconds, but no one will come too close to that because of the above. At this point in the year, I haven't seen anything come close that close to 2.8 s, but i've only been to two invitationals so far.

You are correct- my ~3.1m/s for a falling body was wrong; its the square root of 2gh; sqrt of 19.6

ah, wikipedia, found formulas i wanted :]
time for falling mass to fall 1 meter down is sqrt(2d/g); distance 1m, then t=.452s
velocity after that is sqrt(2gd); v=4.427m/s
10m at 4.427m/s; 2.259s
together, that wud be 2.711s
but i guess the car cud be as long as the ramp/height, and the part extending in front has nearly no mass, and all extra mass wud pullup the car's cg
so there wudnt be extra .452s,
2.26 seconds for zero friction/loss of energy

edit:
accelerate time: .452s
paperclip point 100cm infront of the ideal center-of-mass(1m high), so 9.1m travel distance at 4.427m/s: 2.056s
fastest time for 10m: ~2.50s

uh, air frictional, negligible,
large momentum, mass 2.499kg, so little degradation in speed as car runs.
how, does wheel radius and mass affect speed? i sorta see how spinning it takes up energy..but i dont really get that part..(never-taken-physics person..)
curved ramp with less than .5mm gap to ground, 100cm x 74cm, is there a way to find the efficiency in it conversion of energy?

i consulted a physics professor and did some calculations with him based on the curve of our ramp and the size of the vehicle; the calculations were all wrong; the estimated time was about 4.1 seconds, but our vehicle traveled the 10 meters in about 1.12 seconds. Pretty fast.

sciolymeister wrote:i consulted a physics professor and did some calculations with him based on the curve of our ramp and the size of the vehicle; the calculations were all wrong; the estimated time was about 4.1 seconds, but our vehicle traveled the 10 meters in about 1.12 seconds. Pretty fast.

O.O
I give up. I can't even imagine that...

sciolymeister wrote:i consulted a physics professor and did some calculations with him based on the curve of our ramp and the size of the vehicle; the calculations were all wrong; the estimated time was about 4.1 seconds, but our vehicle traveled the 10 meters in about 1.12 seconds. Pretty fast.

Isn't that impossible given the calculations HenryHscioly, hmcginny, and Balsa Man provided?
Also are you sure there isn't a typo somewhere?

I'm pretty sure he's trolling...... >.>

sciolymeister wrote:i consulted a physics professor and did some calculations with him based on the curve of our ramp and the size of the vehicle; the calculations were all wrong; the estimated time was about 4.1 seconds, but our vehicle traveled the 10 meters in about 1.12 seconds. Pretty fast.

yea, thats a lie, unless your car had a turbine on the top of it.

Frogger4907 wrote: yea, thats a lie, unless your car had a turbine on the top of it.

....or a big spring behind it, or a 2m tall ramp, or, hey, maybe a gravitational field enhancer to crank "g" up.

And, as discussed before, the curve of the ramp will not affect v.....

Maybe he simply has a problem with metric units or doesn't understand the nature of how a timed run is made. On the idea of a 2 meter ramp, no question the speed would be higher but you would also be covering a greater distance and this is an elapsed time event. Our ramp is slightly over 1 meter in length so a 10 meter run is actually just over 11 meters for the vehicle to actually cover. I understand this will be different for each team but all ramps will add to the total distance traveled and the shape will impact the elapsed time, along with friction and several other considerations.

I would love to see a video of the 1.12 sec 10 meter run or at a minimum have them post a correction or explanation so all of our questions will be answered. Our Gravity Vehile runs the 10 meters, actually 11 meters as stated previously, in just under 3.5 seconds. We have lots of timed runs and it is always within a few hundreths and I expect most of that variation is related to the timer not the vehicle. We have excellent bearings and the fact that our 10 meter time is LESS than 2X our 5 meter time seems to confirm that we are not slowing down much between the 5 and 10 meter distance. ( 11 meters is not 2X 6 meters) I don't know if we can improve our ET any more and in fact we are no longer focused on that and working on improving accuracy and calibration.

Good luck to everyone