A lab experiment was performed to find the centripetal force on a rotating body which measured mass(m), frequency(n), and radius(r). It was found that Fc=4Π2n2mr. How do I write an expression for the uncertainty of the centripetal force? Thank you
Let δn, δm, and δr be the uncertainties of n, m, and r, respectively. Then the error propagation law tells us that the relative uncertainty of the product F=4Π2n2mr is
δF/F = 2 δn/n + δm/m + δr/r,
from which you can find δF.
Note: a constant factor (4Π2) does not contribute to the relative uncertainty, whereas the exponent 2 in n² becomes a factor of 2 in the relative uncertainty.
Alternatively, you can compute the total differential of F,
dF = (∂F/∂n) dn + (∂F/∂m) dm + (∂F/∂r) dr
= (8Π2nmr) dn + (4Π2n2r) dm + (4Π2n2m) dr.