Constant Acceleration Equation - physicist please!

  • Thread starter Gregor
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  • #76
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That was not for you, that was for Vey2000, and it was not supposed to be funny.
 
  • #77
39
0
g, m, and s DO NOT FOLLOW THE RELATIONSHIP g= a*s²

How many times do I have to tell you that?

I realize this

the only importance for the formula is that it produces the correct numerical value for 1 g in revised units

and the forumula does this perfectly
as I have demonstrated several times

(to the annoyance of every physicist in the forums)
 
  • #78
2,985
15
the only importance for the formula is that it produces the correct numerical value for 1 g in revised units

Dammit, NO!, it does not.
You do NOT realize it.

Look, 3 + 2 = 5 right?

does 3(apples) + 2(oranges) = 5 (apples)

No. Do you see my point? The math is right, the logic is WRONG!
 
  • #79
39
0
No. Do you see my point? The math is right, the logic is WRONG!

I see you're getting angry now :-(

yes, I've seen the point all along

however it's my point that is being missed

9.80665 (Z) * 0.001 (I) * 0.001 (I) = 0.00000980665 (N)

there are no apples, oranges, or any physical entities here
just numbers to be computed.

the result (N) just happens to be equal to g when m = 1 meter
and s = 0.001 second

the result is always "numerically equal" to g

it's just a convenient coincidence that the formula provides the correct numeric value, there is no direct connexion to physical dimensions involved.
 
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  • #80
2,985
15
the result is always "numerically equal" to g

Ok, fine, SO WHAT? What good does it do if you lucked out and got the same numerical value, but your units are completely WRONG?
 
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  • #81
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how are they wrong?

the only difference between

9.80665 * 0.001 * 0.001 = 0.00000980665

and

9.80665 m * 0.001 s * 0.001 s = 0.00000980665 m/0.001 s/0.001s

is that the units are added in the last expression

this does not make them "wrong", but simply "included" or "not included".

the value for g is correct for these units none-the-less

since 1 g does = 0.00000980665 m/0.001 s/0.001s
 
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  • #82
2,985
15
Dammit are you blind?

9.80665 m * 0.001 s * 0.001 s = 0.00000980665 m/0.001 s/0.001s

does [tex] ms^2 = \frac{m} {s^2}[/tex] to you?
 
  • #83
9
0
cyrusabdollahi said:
You are trying to go to the local drug store by going all the way around the beltway.

I'm aware of that -- I said so myself: "...this is getting needlessly out of the way." However, it's my biased opinion as a student that if you can't see the proper way, the beltway is better than no way. You can't build up a mathematical intuition for how to get from A to B quickly if you don't know how to get from A to B at all.

Unfortunately, it may be the case that despite taking the beltway I still got nowhere since Gregor is still confused.

Gregor said:
how are they wrong?

the only difference between

9.80665 * 0.001 * 0.001 = 0.00000980665

and

9.80665 m * 0.001 s * 0.001 s = 0.00000980665 m/0.001 s/0.001s

is that the units are added in the last expression

No, there is another difference, ignoring the the fact that the dimensions are wrong -- the right hand side of the second "equality" (it's not equal at all) has two additional divisors that are not in the right hand side of the first equality.

Allow me to take a stab at "fixing" your first equation. What you really have is the following:

9.8 m/s^2 * 0.001 (s/s') * 0.001 (s/s') = 9.8x10^-6 m/s'^2

Notice how there are indeed units in there? Notice how s cancels out with s in the left hand side and you are left with s' instead?

Now I'll take a stab at interpreting your second "equation." The two "0.001 s" divisors are in fact the new s' units. Replace it in the right hand side of my proposed equation and you'll recover the right hand side of your second "equation."

So the problem clearly lies in the left hand side. What you are doing by multiplying on the left side by "time" is actually in fact multiplying by the time unit conversion factors -- 0.001 s/s'. This relates to my previous post where I went out of my way to explicitly show you the conversion factors as variables.

The other problem is that on the left hand side you have "assigned" 9.8 the unit of m, whereas it is m/s^2.

So, your "formula" is g' = g * T'^2, where g' is just g in the new units of m/s'^2, and T' is the conversion factor with units of s/s'. -This- is mathematically consistent.

You have to realize that just because things work out in your mind does not mean that what comes out into paper works out the way you write it. As I said, in my opinion the problem was one of definitions.
 
  • #84
Doc Al
Mentor
45,089
1,396
I think we've given this inane thread way more time than it deserved.

Closed.
 

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