...meter stick...

Goal: To find the mass of a meter stick and a 100 g lead weight.

A 100g lead weight, is one individual circle from the image above

Step #1 was basically a demonstration to learn how to balance a meter stick on a table. We attempted this three different times, each time was very different.

In our first demo, the meter stick was not balanced on the edge of the table, which meant it had a torque because torque is lever arm times the force. We got results that looked like this:

Image from Notes

In our second demonstration, the meter stick was now balanced at the edge of the table. We figured out that the edge of the table and the center of gravity related because the center of gravity was sitting right on the edge of the table. It looked just like this:

Image from Notes

And then there was demonstration C; we added a 100g lead mass to the ruler and we had to balance the forces so that we could see the clockwise and counterclockwise torque. That looked like this:

Image from Notes

Step #2 was the "planning" stage before we got to do anything. We wrote down our initial plans to solve the challenge. This was what we came up with:

• w=mg
• torque=force*lever arm
• 100 g = 1 kg (this was for the lead weight)
• We would use w=mg to get any weight of the objects and we use the torque formula when we are balancing the stick and trying to find the clockwise torque.

Step #3: the real deal

This was the part when we used step #2 in order to try out the plan to see if it would work.

ATTEMPT #1

Our first attempt was putting the meter stick (100cm) at the 50 centimeter mark and putting the 100 gram weight on it...if you try this, it immediately falls. It does not balance because the lead weight exerts such a large force on one side only. As you can see in the image below, someone had to catch it because it would not have balanced on its own. Therefore, it failed.

Calculations:

w=mg

w=(.10)(9.8)

w=.98

torque=force*lever arm

torque=(9.8)(50)

THIS IS WRONG. Calculations failed because we did not try to balance the meter stick at all.

ATTEMPT #2

Our second attempt involved us putting the measuring stick on the table and putting the lead weight on it and keep shifting it around until it balanced perfectly. This procedure worked. Below you will see what it looked like:

In the image above, the red arrow represents the force that gravity is putting on this object. The yellow lines show the lever arm of the ruler which you will see when you look own to the calculations. The black dot is only showing that that is the center of gravity.

Calculations:

w=mg

w=(.10)(9.8)

w=.98kg

torque=force*lever arm

torque=(.98)(22.7)

**the way we got 22.7 was by subtracting 77.3 from 100 because that is the length of the lever arm from the meter stick

torque=22.25 Nm

This is not the final answer because we are trying to find the weight of the meter stick.

torque=force*lever arm

22.25=28F

Divide by 28 on both sides.

F= .79

Now that we have the force of the other side, we need to figure out the weight

w=mg

.79=m(9.8)

Divide by 9.8 on both sides

.081kg 

We must convert this back to grams and that gives us 81 grams. THIS IS THE WEIGHT OF THE RULER