Prof. T and most professional physicists care a lot about units. If you have a dimensionful integral you can’t do, that is bad. If you can turn the integral to something with overall units times a dimensionless integral (which is a number like ) that isn’t so bad.
Suppose, for example, the integral integral you are trying to compute is an integral over position:
(B.1) |
where has units of length. Then times a dimensionless number, which turns out to be . You should be able to show the without doing any integrals, by simply switching the integration variable from the dimensionful variable to a dimensionless variable (the position in units of ). Here are the steps
(B.2) | ||||
(B.3) | ||||
(B.4) | ||||
(B.5) |
where is an order one constant. I think that we can agree that
(B.6) |
shows a great deal more insight than Eq. (B.1).
The fact that the proportionality constant is doesn’t seem so important11 1 This value of follows by a change of variables, defining in Eq. (B.4)., and I would be happy with as a result. Finding requires doing a dimensionless integral, which is the only kind of integral you should ever try to do!