What are the dependent and independent variables?

What are the independent and dependent variables of my experiment?

• Hypothesis: If I continually release LN2 (liquid nitrogen) from a pressurized tin can, and I do this for three separate experiments of 5, 10, and 15 seconds, than I believe that the temperature will decrease because... So my question is, what are my independent and dependent variables? These are the variables I am confused over: 1. The temperature of the can. < D 2. The Liquid Nitrogen < I 3. The time period that I release the nitrogen. <D Do I have two dependent variables? What should I put as my independent and dependent variables? Am I approaching this wrongly? Thank you for help.

• Answer:

  I don't fully understand the hypothesis but think of experiments as such: You want to measure a quantity or test a relationship. You then want to determine how successful you've been in measuring the quantity or investigate the correctness of the relationship. Here your experiment involved pressure, temperature, volume and time so it is certainly testing a thermodynamic relationship. Your first question is does varying the time nitrogen is released for change the temperature. Your second question is, what is the relationship between time released and temp. change Your third is, what is the validity of this proposed relationship You might then try to predict the temp. change for 20seconds with a calculated 'uncertainty' You only want one variable for a fair test. You are choosing how long the nitrogen will be released for- this is the independent variable and will be plotted on the x-axis because YOU are changing it. Everything else will be a dependent variable, or simply not related. I think here the only other dependent variable is the temp. of the can. Remember there is uncertainty inherent in all measurements, you may not get 5seconds exactly etc, the stop clock cannot read 5 seconds to infinite precision etc, the temp in the room may effect the readings...