# Homework Help: Pendulum test?

1. Feb 2, 2013

### donniemateno

just wondering has anyone studied this physics experiment before? I have to do it as part of my last year at uni as I didnt do physics at college ( chose mechanics much more interesting!)

anyway its apparently been the same exam for the last 4/5 years but the lecturers give you no help in advance and just give you this equation:

T = 2 * Pi * sqrt(l / g)

T = period (in seconds)
Pi = 3.14...
sqrt = root of ...
l = length of pendulum in m
g = acceleration in m/s^2 (9.81)

I am wondering if anyone has done this experiment but working out G rather than t? if so what would the formula be rearranged? I have found 2 through some googling :

1. g = l/(t/tpi)^2
2. g = 4pi^2L/T^2

Sorry if this is in the wrong section please move if it is

2. Feb 2, 2013

### tiny-tim

good morning, donniemateno!
square this equation, then re-arrange it …

what do you get?

3. Feb 2, 2013

### donniemateno

Quote by donniemateno
T = 2 * Pi * sqrt(l / g)
square this equation, then re-arrange it …
what do you get?

g = sqrt (2*pi*l )/ T?

4. Feb 2, 2013

### tiny-tim

hi donniemateno!

why aren't there more squares there?

5. Feb 2, 2013

### donniemateno

g = sqrt (2*pi*l )/ T^2

I think

Im really not very good at rearranging formulas

I understand the concept of taking one from one side to the other through division but get lost when sqreroots are involved

6. Feb 2, 2013

### donniemateno

a square roots becomes a ^2 so does that mean:

g =(2*pi*l)^2/ T^2

7. Feb 2, 2013

### tiny-tim

ok, then do it one step at a time

first, square T = 2 *π* √(l / g) without any rearranging …

what do you get?

8. Feb 2, 2013

### donniemateno

first, square T = 2 *π* √(l / g) without any rearranging

I'm going to say

T^2=2*pi*(l/g)?

9. Feb 2, 2013

### tiny-tim

T2 correct

(l/g) correct

10. Feb 2, 2013

### donniemateno

is the next step to divide by 2 pi? if so would that be :

T^2 / 2*pi = (l/g)?

11. Feb 2, 2013

### tiny-tim

whoa!!

go back … your 2 *π was not correct …

you needed to square it!

12. Feb 2, 2013

### donniemateno

would pi become 4 pi?

13. Feb 2, 2013

### tiny-tim

yup!

T = 2 *π* √(l / g)

becomes

T2 = 4 *π2* (l / g)

(you see how you have to square each term separately?)

ok, now get g on the left and T2 on the right

14. Feb 2, 2013

### donniemateno

so next if i divide by g to get

T2 / g = (4 *π2* (l / g)) / g

then divide by t^2 to move it over giving me

g = (4pi*l)/T^2

15. Feb 2, 2013

### tiny-tim

divide by g??

16. Feb 2, 2013

### donniemateno

would it become

t^2*g = 4pi^2*l

then

g = 4pi*l / T^2?

17. Feb 2, 2013

### tiny-tim

(you mean g = 4pi2*l / T2 )

yes!!