# Dots on physics equations. What do they mean?

1. Aug 25, 2013

### epislon58

So when there is a dot above the equation it means with respect to time. What does it mean if there are two on the top or one on the side?

2. Aug 25, 2013

### Staff: Mentor

Two on top of a variable usually mean the second derivative with respect to time.
"One on the side" - can you give an example?

3. Aug 25, 2013

### ZapperZ

Staff Emeritus
For future reference, always provide context and sources when you ask something like this.

Zz.

4. Aug 25, 2013

### 256bits

That is a shorthand of writing the derivative. Two dots above would mean double derivative.

One on the side - I don't recall that one.

PS. 0405, 0406, 0408 and they all showed up with my post not before

5. Aug 25, 2013

### Staff: Mentor

One dot on top usually means the first derivative with respect to time (that is, speed), two dots on top the second derivative with respect to time (that is, acceleration).

A dot on the side? Show us an example of what you mean and you'll get a better answer.

6. Aug 25, 2013

### 256bits

perhaps the dot on the side - he is refering to f prime and f double prime - only thing i can think of, only it's not a dot.

7. Aug 25, 2013

### epislon58

This is what I am talking about.

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8. Aug 25, 2013

### Staff: Mentor

I think that is a punctuation mark. Or a misplaced time-derivative point.

9. Aug 25, 2013

### epislon58

Well it so the Euler Lagrange equation. Is it suppose to be there ?

10. Aug 25, 2013

### Staff: Mentor

That's hard to tell from the RHS only, as both derivatives (with and without dot) are interesting.
You can check the units to find it out.

11. Aug 25, 2013

### epislon58

This is the entire equation

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12. Aug 25, 2013

### Staff: Mentor

That is a punctuation mark.

13. Aug 25, 2013

### epislon58

Thank you good sir.

14. Aug 30, 2013

### namanjain

it's just derivative wrt time

.
x = dx/dt
= lim: tâ†’0 in x/t

15. Aug 30, 2013

### CompuChip

namanjain, OP is talking about the second dot.
That's just a period marking the end of the sentence.

16. Aug 31, 2013

### namanjain

ohh! sorry read half of the first sentence
well 2 on top means:

..
x =
d2x
______________
dt2

second derivative

eg if
x=t8 e(t2)

a =

d2x
______________
dt2

get answer using wits,(:tongue: it's short)

aNs

a= 56t6e(t2) + 34t8e(t2) 4t10e(t2)

Last edited: Aug 31, 2013
17. Aug 31, 2013

### Staff: Mentor

namanjain please read the full thread, you are not adding anything new here.

18. Sep 2, 2013

### namanjain

then i suppose discussion is over, thank you

19. Sep 2, 2013

### Staff: Mentor

Over means over, thread closed.

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