physics

Lab_Letter_Guidelines.docx

Lab Letter Guidelines

PURPOSE: Regardless of what STEM field you work in or what your particular job is, you will regularly have to write reports, technical documents, etc. Employers highly value the ability to articulate and communicate how data leads you to a particular conclusion in addition to your technical credentials (Lab Analyses and Letters). Additionally, the audience you write for may not always have a technical background, so learning to write for a variety of audiences is important (Lab Letters). Like any other skill, it only improves with practice and hard work. My goal is to give you opportunities to build your skills as you progress through your scientific education.

The lab letter provides an opportunity to:

· practice communicating scientific ideas in a less formal setting than a typical lab report.

· practice communicating scientific concepts to a non-technical audience.

· revisit the concepts in the lab activity, thereby strengthening the new neural connections forming in your brain.

ASSIGNMENT: The lab letter is a summary of a lab activity we do in class written for a non-physicist. This non-physicist is not fictitious; you will compose and send a letter to a friend, family member, significant other – someone in your life for which you would like to share a little about the physics you are learning.

A good lab letter will:

· be written in the tone of an email. (This means you are conversational, and yet you still need to use correct grammar.)

· describe the experimental set-up/procedure in sufficient detail for a person unfamiliar with physics to understand. Pictures are not required, but they can go a long way in helping someone understand the set-up.

· describe results and their physical significance clearly and correctly.

· have correct grammar and spelling.

· summarize the results (usually a graph) and explain what they mean/what you learned, focusing on the physical interpretation rather than the numbers.

· answer three questions that connect the lab to reality:

· - Why did we do this?

· - What is the greater purpose?

· - How does this tie into your everyday life?

SUMBISSION: Email the letter to your recipient and include Drs. Schoene and Daane on the email. Please include “Lab Letter #,” with the appropriate number in the subject line.

GRADING: We will use an improvement-based grading method to determine the final score for the lab letters. This means if the lab letters show improvement over the quarter, the score for the last lab letter will become the overall score for all the lab letters. If the lab letters do not improve over the quarter, all the scores will be averaged (standard grading method). If a lab letter is not submitted, the lab letter scores will be averaged as well. Improvement-based grading reflects that good written communication is a skill that improves over time, rather than something students are expected to do well from the beginning of the class.

Please see rubric online in the canvas assignment for more information!

Example Lab Letter (I am sorry the pictures are missing!)

Hi Mom,

I am writing to tell you about some cool physics we did in our class recently.

First, here is the setup:

Our experiment is called Balancing a Ruler. We started with a 100 cm ruler, with a set under the 65 centimeter mark. We set this up on a table. This had the ruler offset to one side, meaning it is not balanced. We have created a lever, with a long end and a short end. We next placed a 250 gram weight on the short end, at the 75 cm mark. Note that this is 10 cm from the fulcrum. This weight caused the lever to tilt, until the short end rested on the table, and the long end hung in the air. You may want to check out the picture below to help illustrate the setup.

Next, we used various weights (6 in total) placed on the long end of the ruler, to balance the ruler so that neither end touched the table. First up, we tried a 30 gram weight. We placed this on the long end, and adjusted its position until balance was achieved. We found the ruler balanced with the 30 gram weight 42.3 cm from the fulcrum. The results are shown in the table and graph below.

We found some pretty neat patterns here.

First, notice on the graph, we see that as the weight increased, the distance from the fulcrum decreased. So, more weight used to achieve balance results in less distance out from the fulcrum. We learned that this is called an inverse relationship between weight added and the distance from fulcrum – I think of this as inverse because, as one goes up, the other goes down.

An interesting thing happened when we used the 250 gram weight, we achieved balance at 5.5 cm away from the fulcrum. This is interesting, because the weight on the short end is also 250 grams, but it is 10 cm away from the fulcrum. Why did that happen? This is because the long end and short end of the ruler have different weights. The long end of the ruler weighs more than the short end, and affects the balance. What we observed is a lever. The longer the lever, the less force is required to move it. Moving the weight away from the fulcrum created a longer lever, so less weight (force) was required to achieve balance. Moving the weight towards the fulcrum created a shorter lever, so more weight (force) was needed! So the ruler factored into the balance more than I originally thought.

Another interesting principle can be seen in the data. On the graph you can see that as our curved line approaches either axis line, it seems to “line up” or become parallel with the axis. If we were to continue this experiment with additional trials to gain more data, we can predict the line would continue in the same manner. In fact, the curved line will never cross either axis. On the graph this would be called an asymptote. An asymptote is a line placed on the graph representing a value that our data will approach but never equal. We call this a “limit” of the data. This means that no matter how far from the fulcrum we move, we will always need to add a weight to achieve balance! The weight required will never be zero, although it will get very close to zero. Imagine the lever lengthened equally in both directions. We could go as far out on the long end as we choose, but as long as the ruler keeps the same proportionality, we will always have to add weight to achieve balance. The short end will always rest on the table with zero additional weight.

On the other end of the spectrum, as we use a heavier and heavier weight, we move closer to the fulcrum. The weight must be on the long end of the ruler to result in balancing the lever. We could use a weight of several kilograms, but we will never achieve balance unless the weight is moved away from the fulcrum. Weight will always need to be a distance away from the fulcrum, even though this distance will become very small.

This experiment showed some cool (and logical) principles at work. We were able to set up and conduct an experiment, collect data and create a graphical representation. Our findings revealed an inverse relationship between weight added and distance from the fulcrum. We also found that there are limits to how small the weight could become to achieve balance, and how close to the fulcrum we could move the weight to achieve balance. I feel like because of this lab, I better understand inverse relationships, which are far more common than I ever thought about before. For example, we use this particular one all the time when carrying a tray of dishes, or using a seesaw, or even a baby’s mobile balancing above their crib. I have a feeling this inverse relationship will come in handy when studying more concepts in physics this year.

Big Hugs –

A student