Acceleration question:

sonhouse
Science 21 Jul '08 04:17
1. sonhouse
Fast and Curious
21 Jul '08 04:171 edit
How many G's do you have to do of constant acceleration to get the time through a quarter mile down to 2 seconds or less?
2. AThousandYoung
West Coast Rioter
21 Jul '08 05:12
Originally posted by sonhouse
How many G's do you have to do of constant acceleration to get the time through a quarter mile down to 2 seconds or less?
d = di + vi*t + (1/2)at^2

That's correct, isn't it?

(1/4)mi = 0 + 0 + (1/2)a(4s^2)
mi = 8s^2 * a
mi/(8s^2) = a

So we need an acceleration of 1/8 mi/s^2

One G is 32 ft/s^2

(1/8)(mi/s^2)*(5280 ft/mi) = 660 ft/s^2

~20.6 G's
3. sonhouse
Fast and Curious
21 Jul '08 05:291 edit
Originally posted by AThousandYoung
d = di + vi*t + (1/2)at^2

That's correct, isn't it?

(1/4)mi = 0 + 0 + (1/2)a(4s^2)
mi = 8s^2 * a
mi/(8s^2) = a

So we need an acceleration of 1/8 mi/s^2

One G is 32 ft/s^2

(1/8)(mi/s^2)*(5280 ft/mi) = 660 ft/s^2

~20.6 G's
I did that question because I put the formulae up in the other post!
A=2S/(T squared)
Thats all there is too it.
1/4 mile = 1320 ft so times 2=2640/4=660 Ft/sec squared, divide by 32=20.625.
You just assume starting from zero velocity, simplifies the equation.
4. AThousandYoung
West Coast Rioter
21 Jul '08 05:46
Originally posted by sonhouse
I did that question because I put the formulae up in the other post!
A=2S/(T squared)
Thats all there is too it.
1/4 mile = 1320 ft so times 2=2640/4=660 Ft/sec squared, divide by 32=20.625.
You just assume starting from zero velocity, simplifies the equation.
I know. I'm the kind of guy who likes to start with unsimplified equations and then simplify them; for example, I use Ideal Gas Law even if Boyle's Law will do the job.
5. 21 Jul '08 05:53
I'm surprised that engineers in US is still using feet and miles. It's like a duck pond with their own units stubbornly used.
Whats wrong with SI-units, as used in the rest of the civilised world?

How about NASA, they have started using the international measuring system, don't they?
6. AThousandYoung
West Coast Rioter
21 Jul '08 07:54
Originally posted by FabianFnas
I'm surprised that engineers in US is still using feet and miles. It's like a duck pond with their own units stubbornly used.
Whats wrong with SI-units, as used in the rest of the civilised world?

How about NASA, they have started using the international measuring system, don't they?
It's mostly habit and infrastructure issues at this point. Yes, NASA's on SI, and the different units actually caused problems for some rover or something.
7. 21 Jul '08 08:02
Originally posted by AThousandYoung
It's mostly habit and infrastructure issues at this point. Yes, NASA's on SI, and the different units actually caused problems for some rover or something.
Yes, I read something about that. Some mixup between inch and centimeters, wasn't it?

At university level, what kind of units are used, nowadays?

England switched to decimal system in some respect, Australia has done it. How much progress is US doing?

Noone thinks that 100 cents on a dollar is awkward. On the other hand everone accepts 60 minutes an hour... ðŸ˜•
8. AThousandYoung
West Coast Rioter
21 Jul '08 08:06
Originally posted by FabianFnas
Yes, I read something about that. Some mixup between inch and centimeters, wasn't it?

At university level, what kind of units are used, nowadays?

England switched to decimal system in some respect, Australia has done it. How much progress is US doing?

Noone thinks that 100 cents on a dollar is awkward. On the other hand everone accepts 60 minutes an hour... ðŸ˜•
They tried to change the clocks, but it never caught on.

In science we use SI. In engineering they use Imperial (feet).
9. 21 Jul '08 09:00
Originally posted by AThousandYoung
They tried to change the clocks, but it never caught on.

In science we use SI. In engineering they use Imperial (feet).
This means that I can tell an engineer from a scientist bu just asking him how tall he is?
Does he answer 6 foot 8, then he is an engineer. Does he answer 180 centimeter, then he is a scientist. Does he answer 4 gallon, he is... eh, what?

How tall are you, AThousandYoung?
10. sonhouse
Fast and Curious
21 Jul '08 09:00
Originally posted by FabianFnas
I'm surprised that engineers in US is still using feet and miles. It's like a duck pond with their own units stubbornly used.
Whats wrong with SI-units, as used in the rest of the civilised world?

How about NASA, they have started using the international measuring system, don't they?
I put it in miles because the standard drag race in the us is the quarter mile. Imagine this conversation:
Well Bubba, how does that thing run in the 402.34?
HUH, wat de haill you talkin bout?
402.34 meters hogbreath, its a quarter mile. Jeesh.
11. 21 Jul '08 09:05
England now uses SI units at university level for all it's science. In fact, in England SI units are used all throughout primary and secondary school aswell (I think primary school is equivelent to elementary school and secondary is equivelent to high school, but not sure.)

Also, SI units are used pretty much everywhere in England. All transactions need to be in SI units because of the European Union laws, it caused some upset when it happened but is now widely accepted.

Saying this though, the older generation (my parent's generation) are not so good at using SI units. They still work in Imperial units for most things (like mass and distance), but this will change as the new generation are never exposed to the old units.

The one exception is road signs; distances on road signs are in miles, not km.
12. sonhouse
Fast and Curious
21 Jul '08 11:141 edit
Originally posted by MattP
England now uses SI units at university level for all it's science. In fact, in England SI units are used all throughout primary and secondary school aswell (I think primary school is equivelent to elementary school and secondary is equivelent to high school, but not sure.)

Also, SI units are used pretty much everywhere in England. All transactions need to e old units.

The one exception is road signs; distances on road signs are in miles, not km.
Maybe the US should join the EU...
Let's see, EUUS USEU SUUE...
13. 21 Jul '08 11:291 edit
Originally posted by sonhouse
Maybe the US should join the EU...
Let's see, EUUS USEU SUUE...
Joint Europe States United States - JESUS - Oh no...
14. sonhouse
Fast and Curious
21 Jul '08 11:39
Originally posted by FabianFnas
Joint Europe States United States - JESUS - Oh no...
Or Bush Lead European Democracy. BLED.
15. 21 Jul '08 12:00
Originally posted by AThousandYoung
They tried to change the clocks, but it never caught on.
The thing with metricising the clocks is that you can't do it thoroughly. You can have 10 days to the week, 10 hours to the day, 100 minutes to the hour and 100 seconds to the minute, but what you can't do is make the Earth go round the Sun in exactly 100 times the period in which it turns around its own axis, nor make the Moon go round in a neat number of days.
So while you can give us 100 cents to the euro, and 100 cm to the metre, instead of 12 pence to the shilling (or was it 12 s. to the L.?), or 13 furlongs to the firkin, and have that whole system completely stitched up with round factors to the last unit, no matter what you do with time, you'll always end up with weird factors there. So, most people apparently conclude, you might as well not bother to come up with half a solution.

Richard