Mass of the Meter Stick Lab

In this Lab, we were tasked in finding the mass of a given meter stick by using our knowledge of balance and torques. We were told to use a meter stick and a lead weight that weighs 100g. Once we had done our calculations, we would check the mass we got by actually weighing the meter stick and comparing the numbers. So we began....

Step 1:
First we did some demonstrations in order to better our understanding of torques, and to bestow on us the tools we need to find this information(the mass of the meter stick).

Here are the demos we did:

These exercises really helped us figure out the information we needed to gather and compile. We began to learn how to use the information we had to find more information.

Step 2: 

We began to plan after doing these demos. The demos were written in to solidify our ideas about balancing, but the planning was all vocal. We started to set it up and talk through way we might be able to calculate the mass.

Step 3:

Steps 2 and 3 bled together because trying out ways to find the mass were simultaneously our plans for doing them. The planning and the doing were not separate but we did them at the same time.

What we tried was a lot of writing numbers down and figuring out how they fit together. This is what finally worked:

We started by finding the Center of Gravity for the stick without the weight on it by balancing it on the edge of the table. It didn't end up being 50cm, it ended up being 50.3 cm. Then we added the weight to the end and tried to find the Center of Gravity again. That number we found was 28.7 cm.

Then we had to figure out what to do with those numbers. We knew that the meter stick was balancing, and when things are balanced, it is because their clockwise torque and counterclockwise torques are equal. We set up the equation that we set up in the demos to use the lever arms and force on one side to find the force on the other side.

clockwise torque=counterclockwise torque
Force * Lever Arm = Force * Lever Arm

Then we plugged in using .98 N instead of 100g for the weight because it needs to be in Newtons to be a force. We knew that 50.3 cm was still the center of gravity, so we subtracted 28.7 from 50.3 to find the lever arm of the side of the stick resting on the table. We got 21.6 cm, and used it as the lever arm for that side of the equation.

(.98) * (28.7) = (F) * (21.6) 

We found that the force on the right side(aka the entire meter stick, because we used that Center of Gravity) was 1.3 Newtons.
We converted that into mass using the w=mg equation because what we found with the torque equation was the weight of the meter stick. We use that equation to convert it to mass, which is what we are looking for and what we will measure. We found that the mass was 130g.

When we weighed it it was actually 120g. So we were off by ten grams which is kind of a bummer and void of satisfaction. Oh well, we learned about Physics anyway.

Here is a picture of our field notes:

Here is a Drawing of what is going on:

Resource Blog

Torque resource:

This resource is a Khan Academy tutorial/introduction to Torque. I found this video surprisingly informative because I had only seen a couple of science Kahn Academy videos but did not find them incredibly helpful. The ability to draw and animate movement by use of the medium he uses helps the effectiveness of teaching. It does teach the information a little bit differently from the video Ms. Lawrence made which is similar in style which may be confusing, however, it may also be very helpful. I found it helpful.

Link:

Introduction to torque: An introduction to torque


Center of Mass/Gravity resource: 

This page is a blog post on a blog I hadn't heard of but is apparently made by or funded by PBS. This source integrates torque in as well which helps to relate them. The flow of the post is intuitive and east to follow, and it begins with an example to strengthen understanding through real-life. Over all I found this source very helpful.

Link:

http://www.pbs.org/opb/circus/classroom/circus-physics/center-mass/