[R] Using uniroot on c(0, 1) when the function does not change sign in this interval?

[mviljamaa]

How can I use uniroot to find a root in the interval (0,1) when my 
function does not change sign in this interval.

I've tried plugging in some values and seems like e.g. f(50) < 0 and 
then I can pick c(0,50). But this sounds really weird, given that I need 
to find a root in (0,1).

So what are my options? Perhaps another function?