## Need help with acceleration/time physics...

Member
Posts: 90
Joined: 2006.11
Post: #1
Uhh.... I am making this little game involving a physics engine... and i forgot my formulas... and I can't find them on the web... what is the formula to find out the time taken for a straight line journey, if you know the constant acceleration and distance? I have 'worked out': time=sqrt(distance/acceleration) but it doesn't seems to be quite right... any help?
Sage
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Post: #2
your forumla for time is correct.

Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
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Post: #3
ummm...giyf

anyway, 0.5*a*t^2=d, so t = sqrt(2.0*d/a)
Sage
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Post: #4
v = u + at
s = vt

u (initial velocity) = 0
s = a * t * t
t = sqrt(s/a)

Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
Sage
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Post: #5
Nope, you need calculus to do that correctly. DoG is right.

s'' = a
s' = v1 + a*t
s = s1 + v1*t + (a*t^2)/2

Ignoring displacement in general, or the intial velocity, you get d = (a*t^2)/2.

Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.
Sage
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Post: #6
*sigh* it can all be done without calculus

v = u + at
s = 1/2 * (u + v) * t

u (initial velocity) = 0
s = 1/2 * v * t * t
t = sqrt(2*s/a)

its been too long since I did physics

Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
Sage
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Post: #7
Not to drag this on, but I'd like to point out that s = (u + v)*t/2 is using calculus. It's finding the area under the trapzoid in the velocity graph to determine the displacement.

Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.
Sage
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Post: #8
Yes, but all these forumla can be derives without calculus..

Newton developed these equations before he invented calculus.

v[bar] = s / t
v[bar] = average velocity = 1/2 ( u + v )

Sir, e^iÏ€ + 1 = 0, hence God exists; reply!
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Post: #9
Even if he didn't call it calculus back then, it is still calculus.
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Post: #10
uhh... Thanks guys....

(notices that unknown has 1337 posts under is belt.)
Sage
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Post: #11
Yep, no problem. We always enjoy bickering over questions.

Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.
Member
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Post: #12
Skorche Wrote:Not to drag this on, but I'd like to point out that s = (u + v)*t/2 is using calculus. It's finding the area under the trapzoid in the velocity graph to determine the displacement.
Yes, but in this case u=0 so the formula is really finding the area under a triangle.
Even when u != 0, the formula can be derived using the quadratic formula. Would you consider that calculus?
Member
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Post: #13
Whoa, I looked into my notebook and found this:
d = ut + 1/2atÂ² therefore
0 = 1/2atÂ²+ut-d using the quadratic formula yields:
t = (-u + sqrt(uÂ² + 2ad)) / a

Can this be simplified or something?

P.S. I don't think I used Calculus

---------------------
I'm confused
Sage
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Post: #14
I don't believe that can be simplified any further.

Once again, while you didn't use any calculus, the formula d = ut + 1/2atÂ² is derived using ideas from calculus.

Scott Lembcke - Howling Moon Software
Author of Chipmunk Physics - A fast and simple rigid body physics library in C.
Sage
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Joined: 2005.07
Post: #15
yeah but the idea of v-bar, average time for an entire journey is not derived from calculus, neithe was anything in my post. (the one that I didnt make a stupid mistake in that is)

Sir, e^iÏ€ + 1 = 0, hence God exists; reply!