The physics of the Powertower. So as previously mentioned in another blog, on the Saturday practices we do stations. One of the stations is doing sprints with THE POWERTOWER. What’s a Powertower you ask? Well if you have ever been to the pool and seen those giant red buckets attached to the metal frame thingy, that’s the Powertower. I’ve included a picture because I’m guessing none of you know what I’m talking about.

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Anyways we fill the buckets with water and a belt is hooked up to a pulley system so when we swim with the belt on, we lift the bucket. The station we do involves us sprinting 10.5 yards for time while pulling the weight of the bucket. We have a time range that we are supposed to be in and if we are under the range, we increase the weight.

So initially I wanted to try to calculate a reasonable power ratio for myself while on the Powertower station. Unfortunately I underestimated the complexity of doing this. Even if I neglect the fact that the string has mass, the pulley has mass and the pulley system has friction (the pulley system is fairly complex and probably has a fair amount of friction) I still wouldn’t be able calculate my power. I would need my acceleration off the wall and my drag force experienced at my max velocity. The acceleration I figured I could estimate, but I realized that I couldn’t accurately calculate my drag force which I needed to find the average force I applied during my swim.

Then I realized I could just calculate the power through the power tower alone which is far simpler and actually realistic to calculate. I swam 10.5 yards in 5.9 seconds while carrying 65 pounds. This is equivalent to 9.6 m and 289.13 newtons. Because of the pulley system the bucket doesn’t raise it self by 1 meter for each meter I swim forward. Instead swimming 9.6m only lifts the bucket .8m. The force used to lift the bucket is the weight of the bucket + mass*acceleration. Using kinematics, I calculate the acceleration to be .0459 m/s^{2} and thus the net force to be 1.36 Newtons. The total force is therefore 290.5. Since Power is Force * Distance / time, the Power ratio is 290.5 Newtons * .8 m / 5.9 seconds = 39.4 watts. Just to put this in perspective, a typical light bulb’s power ratio is around 60 watts (I think). Although my actual power rating would be much higher, the power through the power tower is just a small fraction of my power ratio.