Mass and Speed and Acceleration! Oh My!
This past week in class we did some physics-type experiments… some of my most hated moments in high school were in physics. Trying to learn all the equations and plugging them into each other? Not a fun day for me… Blowing things up and making rockets though? Way more me. This experiment was much more simple in comparison though, just a pulley system where we calculated things like acceleration, mass, battery discharge, speed, power level, etc.
To get all of these numbers, we took the pulley system (a pole, with a NXT arm, with a string going to the top where there was another wheel) and added weights to the string at the top. First we left the same weights on there, which was .2 kg of mass. With this we changed the power level 4 times to get some different results. We then did the opposite where we left the power level at 50 and changed the mass 4 times. You can see the results in the picture below.
The following graphs will show what we ended up comparing and what those results were. Many of these results are obvious things that we see on a daily basis but don’t really think about. Like if a girl who was 15 were to try and pull a piano across the city by hand vs. Bruno Mars, a grown man doing it in his music video. Obviously Bruno (A grown man with more weight and strength) could do it, well he could do it easier at least, than the 15 year old girl that weighs no more than 120 lbs. All of these results will be common sense when you look at and think about them.
When comparing the acceleration to the power level, we saw an increase. This graph to to the left shows that with the trendline obviously moving up rather than down. When we increased the power level on the motor, the acceleration increased as well. This is becuase something will accelerate faster if there is more power behind it.
Next we compared the acceleration to Mass (w/fixed power level). This showed us that when you increase the mass of something, the slower the acceleration will be, as the trendline shows in its decreasing motion. Somewhat like the graph above, but with mass now, obviously if you add more mass to something its going to take longer to start moving. Like in that Freddie Munez movie on the Disney Channel when we were 10, he put weights into his box car and it went slower.
In this graph, we see that the trendline is increasing again like the first one. This shows that when we increased the power level from 25 to 55 the power used increased too. This is something that more obvious than the rest. If you are going to make something go faster or more powerful, in this case the motor pulling the weights, than the power that is needed to do this will also increase. Like when we try to heat our apartment, the bill goes up an arm and a leg when we increase the heat becuase the heater needs more power to the system to heat the apartment more.
This last graph goes along with the one from above where we showed that the higher the power level, the more power is needed behind it. This, however, shows it differently. Instead, now we have increased the mass in increments. Like above, when you increase the power level, the power used increases, here though, it is when you increase the mass. The more something weighs, the harder it is to pull/push, and the more power you’ll have to put into it. Now that I explained that, we can get into the actual point here.. When you use more power (even if the power level stays the same more power is needed becuase of the mass increase), that motor uses more of its battery to back that power used. So here we increased the mass and it used more of the battery becuase that little NXT arm couldn’t pick up .2kg all that easily, it needed some extra help with power, using more battery.
These graphs are pretty easy to understand just by looking at them, even without my wordy explanations. If you just look at them and think about it, you can see it. With that, you could easily look back onto your day and pretty much use any of these rules we just showed to explain things that happened. Like why that T bus took forever to go when the light went green, but that line of little smart cars next to you all hit their pedals and moved like the speed of light. If you didn’t get it… Its becuase that T bus had more weight in it and took longer to accelerate. Well now you’re all ready to explain your daily complaints in a scientific way and why you’ll never pull up behind a T bus in Boston again!