GS 104 Lab Report: Data and Meaning
GS 104 EV Lab Report: Kinda Pisa
I) Force and Mass :
While forces are really familiar to us in our daily lives we still harbor incomplete understandings and ideas about forces. In this lab we will try to bring some of those incomplete ideas to the surface and explore them. The goal is for you to establish the conceptual relationship between force and mass that underlies Newton's Laws which collectively form one of the pillars of classical physics.
The experiment itself is fairly simple. You will place one of your lab partners in a rolling computer chair. Using a spring scale, which measures the amount of force being applied, you will pull them down the hallway in different ways while keeping track of the things like speed (velocity) and acceleration.
We will begin with a picture. As we (hopefully) discussed in class pictures are a critical part of the science communication process. This idea applies equally in math as affirmed by the following excerpt of a communication with Galileo Galilei who was a physicist and mathematician.
[A] mathematician, however great, without the help of a good drawing, is not only half a mathematician, but also a man without eyes.
Lodovico Cigoli to Galileo Galilei, 1611
In physics a picture which describes the forces we think are involved in some problem is called a freebody diagram. We will refer to it as a force picture for now. Make a rough sketch of the object you are interested in and indicate the direction of each force acting on the object and give it a clear label.
As you approach the task of doing the force picture (freebody diagram) consider the non-contact and contact forces which might be acting on the person and the chair collectively. For each force you put on your drawing list the two partners which "produce" the force. (If you ignore air resistance you will probably find 4 forces)
II) Data: You will be performing two different experiments. In each case you need to repeat the experiment with three different people sitting in the chair so that you can generate enough data to make a plot later. You may well find that you will have to repeat each part of the experiment to get consistent results. Keep track of all of your data as you do so.
Experiment I: You have some idea what it means to move with constant speed. What I want you to determine is what force do you need to apply (with the spring) to the person in the chair to KEEP them moving at a constant speed down the hall (give them a little push to get them going first)? Does this depend on the mass of the person in the chair?
Experiment II: The second experiment involves applying a constant force which is large enough to make the person in the chair speed up. From the data in your first experiment choose a force larger than that required to keep the "heaviest person" moving at a constant speed. Now the difficult part, apply that CONSTANT force to each of the different people in the chair and record how long it takes to speed up to a "fast walk". You will need to define what a fast walk means and try to reproduce it in each experiment. Again, record all your data for future use.
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IIIa) Plotting:
Experiment I: Plot the force required to maintain constant speed as a function of the mass of the person and the chair. The force will be in Newton's and the mass will be in kg. Some unit conversion may be necessary
Experiment II: Plot the time required to reach your target speed as a function of the mass of the person and the chair. The time will be in seconds and the mass will be in kg.
IIIb) Sloping:
Experiment I: From your plot determine the rate of change of the force with respect to mass. Show all of your calculations and be clear how it all relates to the data you took and plotted.
Experiment II: From your plot determine the rate of change of the acceleration time with respect to mass. Show all of your calculations and be clear how it all relates to the data you took and plotted.
IV) Analysis (What might it mean?):
The core process of science is to take the data and then sit down and look at it and see "what it says". You have some data and some relevant calculations about how people in chairs behave when pulled by forces. What does your data have to say about the following questions. Be careful, I'm not asking what you think the answer should be or what other experiences you have had suggest but specifically what the data you took in this lab has to say about the situation.
I) Does the force you needed to keep the person moving at constant speed depend on their mass? How strongly (you will need to figure out some why of expressing what you think this means)?
II) Does the time you need to get the person "up to speed" depend on their mass? How strongly?
III) Does your data suggest that the mass plays a bigger role in experiment I or II? How do you know this from the data?
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