# Day 64: My Mess from Yesterday Successfully clean up

Yesterday I explained how I totally screwed up my first mod class in a failed attempt to develop N1L.  As I mentioned last time, I opened the class by stating that we needed to start over because I had made a rather huge mistake. At that point most of the mod oners had their interest piqued.  I explained that I thought I could develop this new idea better, but because I had not used the equipment to work it through, but had only worked ii through in my mind I made a glaring omission/mistake.  I apologized and we moved on.

Here was the set-up I used.

Imagine the ‘cart’ was really two dynamics cart attached with the velcro.  Mounted on each was a WDSS set up to measure the forces.  (Sorry, forgot to take picture). The task from the handout  was to use both tension forces to get the cart to move to the right with a constant velocity.  Yes, most said to try it by making the right side force bigger.  I gathered the data and it showed constant acceleration (I should have snapped a screen shot).  The next step was to try even sized tensions.  Here is the data:

Pretty nice data showing that balanced forces create constant velocity.

The next task was to get the cart to move to the right slowing down, stop for an instant then get faster to the left.  We talked about I would not be able to change tensions mid-way (which helped some kids) so they tried the left side force bigger.  Here is the data:

Again, nice data showing that unbalanced forces cause a change in velocity (or acceleration).  Put the two ideas together and we can say the only way to change the velocity on an object (or to make it accelerate) is with unbalanced forces… balanced forces will not change the velocity so if it started at a constant velocity of 0 m/s it will stay ….. you know the rest… Boom N1L.

In hindsight, I should have added an acceleration graph to show that the acceleration is in the same direction as the bigger force.

General Physics:

After a bit more stack-o-graph practice, we started in on the Phan Cart predictions.  Just like we did with the Advanced class, we will use the actual graphs to practice solving constant acceleration problems using v-t graphs.