# F15 Mechanics Week 3

Day 1: Vectors in the four lenses, proving energy formulas.

Day 2: Springs and potential energy graphs.

All Week!!!: the United Nations University/Cal Poly Disaster by Drought Summit, right here at Cal Poly. Are you going to some talks? I am! I’m going check out a talk Tuesday about poverty and climate change, but there are talks all week.

Before Class

During Class

• Big Exam #2 – Midterm #1 is NEXT WEEK TUESDAY. If you hand in formula sheet with exam, I’ll check your formula sheet and make sure that everything is correct and relevant. Make sure it reflects your understanding.

After Class

Day 3: Friction and potential energy graphs PS #3 is posted
Before Class
-Hey! somehow LON-CAPA got messed up yesterday (by me). So, if you were unable to do the problems, don’t worry. I’m working on it.
– Attention! – I don’t have a video for friction. Please read a few pages in your book.**

• Friction – read section 5.1, but don’t read example 5.1 because we do inclined planes (two dimensional problems) after the first midterm.

Goals:

• Dynamics: Friction is a force = to the product of the coefficient of friction and the normal force between two bodies.
• Dynamics and momentum: Friction acts in the opposite direction of the relative motion of the two bodies exchanging momentum. So say, you are spinning your car’s tires when the light turns green. The tires are moving backwards relative to the ground. This pushes the tires forward and the ground backwards. You can see this especially when some of the road gravel flies backwards.
• Energy: Friction turns kinetic energy or mechanical work into heat energy. In the above example, the tires and road get hot. In drag racing, the cars melt some rubber down on the starting pad by spinning their tires.

During Class

• Discuss Projects

After Class

Day 4: Elastic Collisions, PS #3 is posted. I added a 4th problem Thursday morning.

Before Class
Read section 8.4 in the text and the previous sections to provide background – 8.3 may be new to you and worth the look. You can solve the elastic collision with the simultaneous equations as they do in example 8.4, conserving both momentum and energy. However, you could also solve this by drawing pictures as I do in the Educanon video posted for today.

During Class
More examples of elastic collisions

After Class