Problem with relationship of mass and radius with time in centripetal force

[805906000]

We did a experiment, and the aim was to find out that relationship between mass and radius with period of time in the circular motion..Although I know the formula for centripetal force, but I am not sure about what the expression should be

The lab data :
Table 1: 1st experiment : relationship of mass and period
Mass Average time for 20 revolutions (+ 0.5 s) Period (T/20) For 1 revolution
1 25 15.355 0.76183
2 50 12.315 0.61575
3 100 7.53 0.365
4 150 6.66 0.333
5 200 5.635 0.28175
Radius: 35 cm (+ 5cm)
For this one I kind of get the expression, which is t= 1/√m times √4radius pie square (which the value is about 4) so 1/ root of mass and times 4.

Table 2: 2nd experiment: relationship of radius and period
Radius Average time for 20 revolutions Period (T/20)
For 1 revolution
1 10 6.595 0.32825
2 20 7.60 0.38
3 30 8.175 0.40875
4 40 9.35 0.47525
5 50 10.615 0.531
Mass: 25g (+ 1 gram)

And this one, I have not idea about the relationship of radius and period， can anyone help me out with this ? Thanks a lot!

p.s. the lab has systematic errors, since the angle can't be horizontal, cause we swing the object by hand.

 

[gneill]

In the experiment, which mass is being varied? The mass of that's being whirled around, or some counterweight?

What do these cryptic messages mean:

"Radius: 35 cm (+ 5cm)"
"Mass: 25g (+ 1 gram)"

Have you plotted your results?

 

[805906000]

The radius is the same for all the first trials(for determining the relationship of mass and time), and the mass is also the same for all the second trials(for determining the relationship of radius and time)

 

[gneill]

The radius is the same for all the first trials(for determining the relationship of mass and time), and the mass is also the same for all the second trials(for determining the relationship of radius and time)

But what are "+ 5cm" and "+ 1 gram"? Are these meant to represent uncertainties in their values?

 

[gomunkul51]

this might help you:
http://en.wikipedia.org/wiki/Pendulum

also, I'm sure you were supposed to use some kind of computer program (may be Excel) or were given a system to average out the numerous results you got and their errors, so you can get a single representative result (via theory) and it's error.

 

[805906000]

Thanks for the reply;
-Yes,The + 5cm/1 gram are uncertainties
-No,Excel cannot figure out any formula
-The experiment is not a pendulum, it is rather looks like: http://www.stmary.ws/high school/physics/home/lab/Centripetal_Force_Lab.htm

Actually,I would like to just find out the relationship between time and radius supporting by data and deriving some kind of formula, like the one I kinda figure out for the first one about mass and time (t= 1/√m times √4radius pie square, which is derive from centripetal formula)

 

[gneill]

Thanks for the reply;
-Yes,The + 5cm/1 gram are uncertainties
-No,Excel cannot figure out any formula
-The experiment is not a pendulum, it is rather looks like: http://www.stmary.ws/high school/physics/home/lab/Centripetal_Force_Lab.htm

Actually,I would like to just find out the relationship between time and radius supporting by data and deriving some kind of formula, like the one I kinda figure out for the first one about mass and time (t= 1/√m times √4radius pie square, which is derive from centripetal formula)

Your uncertainties should probably look something like

R +/- 5cm
M +/- 1gm

To find your relationship between Radius and Period (for the second experiment), you'll have to write out the equation which equates the centripetal force with the weight of the counterweight, and isolate the desired terms. You may need to use another expression to express the velocity in terms of the period and radius.