[cuongt]

well im about to do a prac and we have to know 3 factors that need to be constant and give reasons to why. well i know that the volume of water has to be the same for all, experimental conditions the same and same initial temp of water but i dont know why or even if i know these 3 r right.

thanx for help 

[xiankai]

elaborate on experimental conditions

[constant thinker]

Is this a lab? A theoretical situation? A pen and paper practice?

I don't see what context you're doing this "prac" (I'm assuming practice) is in.

Those do seam like 3 factors you'd want to keep constant. Remember in an experiment you want to decrease the number of variables. Your second factor seams pretty broad though. Water volume and initial temperature would be an experimental condition, at least to me I'd lump it in there. Pressure may be a factor you want to control.