I have access to a remote controlled submersible and I want to use it to do some physics with some students of mine. We are examining Newton's Laws. I intend to use spring scales to determine the mass of the sub and the max force the sub can exert by applying full forward thrust while reading a spring scale attached to the sub. We'll then have the sub push floating containers of various weights across a tank to record the times. We'll use Δx = ½ a (Δt)^2 and F=ma to calculate the acceleration for each trial and then compare the results. My issue is that this is good as far as it goes, but... 1. Δx = ½ a (Δt)^2 will yield bad data because acceleration won't be constant. 2. F=ma will yield bad data because we can't calculate the force of friction (drag) to determine the net force. I think it will be worth doing to get practice collecting data and making calculations as long as we discuss the previous two points, but I'm looking for some help in making the calculations a little more realistic. Any ideas?