February 9, 2011

Hey grade 12's, excuse my late post, I had trouble logging onto the student web mail on the Daniel Mac website.

During yesterday's class we discussed deriving formulas from position-time graphs. There is 2 types of graphs where you can derive equations from.

Graph 1:

This graph has a linear relationship and only focuses on one velocity meaning the velocity is constant. We use the equation v=d/t for this graph.

Graph 2:


This graph has a power relationship because it focuses on more than one velocity meaning the velocity is changing.

The formulas we derive in class are coming from the power relationships.
Example:


If given a graph like this, you can derive equations from it.
First find the area of the red rectangle, the formula for finding the area is (length)(width) which in this case is (velocity)(time).
Second find the area of the blue triangle, the formula for that is 1/2(base)(height) which in this case the base is acceleration and the height is (time)²
After completing that, you add the two together,
d = v₁t + (1/2)at² and you got your displacement formula!

**PLEASE REMEMBER** If given a question that starts off with something like this: An object starts at rest and it reaches a certain speed, it has two velocities not one. So don't use the formula v=d/t!!

You need to know how to derive equations from the graphs, so please read your notes or ask others or Ms K. for help if you don't understand! We also corrected the worksheet that we were given to on Monday, we also received a Study Guide and two other worksheets on Acceleration.

Next scribe is THOMAS, his post should be posted later on tonight. :)