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Re: Gravity Vehicle C
Posted: March 12th, 2012, 8:22 am
by chalker
Here's a fun thought experiment:
Let's assume the vehicle in question was suspended 10 m above the target line in a vacuum and then dropped. How long would it take before it hit the ground?
The formula to calculate this is basic physics: distance = 1/2 * gravity * time * time
Solving for time: time = sqrt (2 * distance / gravity)
Thus time = sqrt (2* 10m / 9.8 m/s^2) = 1.43 seconds
Therefore, we can conclude that the theoretical fastest time an object starting at rest can move 10 m away due only to the force of gravity is 1.43 seconds, if dropped straight down in a vacuum. In reality the times seen in this event will be much longer than that due to the fact we aren't running in a vacuum, nor are we dropping straight down, nor do we hit a wall and come to a sudden stop at the 10m mark.
Re: Gravity Vehicle C
Posted: March 12th, 2012, 1:11 pm
by illusionist
Stingray355 wrote: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
You guys need to learn to recognize a troll when you see one...
Re: Gravity Vehicle C
Posted: March 12th, 2012, 4:56 pm
by Stingray355
I think you are probably correct it seems he also claims some other impressive performances in at least one other event. I only read the GV post when I posted my comment. I hoped that if he simply made a mistake it would open the door for him to come back and correct it and get some needed assistance from this resource. Over the past 5 years I have dealt with a pretty steady stream of hard working and smart kids that show up for competitions with a device that clearly does not reflect the rule requirements. I always try to use it as an opportunity to show them where they are out of spec and point them in the right direction to to find a revised design, First stop is almost always a complete reading and understanding of the rules. SO is all about kids learning about science and working as an individual as well as being part of a team. Kids are kids and if someone is goofing around trying to get a response by posting obviously bogus info, getting a rise out of the other members may be exactly what he desired. At this point in the season I can't imagine there are very many people that would take 1.12 for 10 meters as a serious or accurate report.
Thanks for the advice and again good luck to all.
Re: Gravity Vehicle C
Posted: March 12th, 2012, 5:46 pm
by chia
I have a possibly silly question: is there any reason not to maximize the height of the ramp?
Re: Gravity Vehicle C
Posted: March 12th, 2012, 5:50 pm
by chalker7
chia wrote:I have a possibly silly question: is there any reason not to maximize the height of the ramp?
There is no performance reason, but some teams might want to reduce the dimensions of their ramp to make transportation easier.
Re: Gravity Vehicle C
Posted: March 13th, 2012, 6:07 am
by Flavorflav
The Gold medal at our regional was won with a 75 cm ramp. Turns out that it was not a strategic decision - he simply misread the rules. He did everything else right, though, and was only marginally slower than the fastest cars with a better distance score. Lower = slower, but you might see a benefit to accuracy.
Re: Gravity Vehicle C
Posted: March 13th, 2012, 10:12 am
by Half-Blood-Princess
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.
Whoa! Holy crabbbp that is really fast!!! ours goes about 4.1 seconds for 10 meters. and we got second place at regionals!!!
Re: Gravity Vehicle C
Posted: March 13th, 2012, 12:15 pm
by Balsa Man
Half-Blood-Princess wrote: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.
Whoa! Holy crabbbp that is really fast!!! ours goes about 4.1 seconds for 10 meters. and we got second place at regionals!!!
As discussed on the previous page, its.....horse feathers, to put it nicely. On the helicopters thread, he says "oops, typo, 2.12 seconds", which is also horse feathers; the physics is what it is
Re: Gravity Vehicle C
Posted: March 13th, 2012, 4:33 pm
by illusionist
Anyone have tips to reduce the recoil that comes with the string braking method? It's consistent to within 2cm per run, but that's not as precise as what I'm looking for.
Re: Gravity Vehicle C
Posted: March 14th, 2012, 12:08 am
by _HenryHscioly_
I haven't built a string braking system before
Does it stop both axles?
Does stopping both sets of wheels in any type of braking system diminish skid?
surface area doesn't affect friction, I think..
but as for mass? if one set is still spinning, then, less force on the sliding wheels, so will skid longer?
I use the wingnut method, is it a good idea to add a second brake..?