# HP Cycle 11

## 11/3 - 11/8

F 11/3

M 11/6

T 11/7

W 11/8

### 🟢 5: F 11/3 - friction recap

Today, if you haven't finished the friction lab, we'll start there for about 15 minutes. I will collect the Friction Lab worksheet Monday, November 6th, but you really should be able to finish it in class.

Then, we'll begin considering friction in our problems by reviewing the concepts that we should have taken away from the lab and then formalize the concepts in Friction Powerpoint. We'll also do some sample problems in the Friction Powerpoint.

If you have any questions about the material presented today, watch the video below. If there's any time remaining, you may start the problems from the next post.

Presentation: Friction Powerpoint

Homework: Quiz on Newton's 2nd Law problems (including elevator problems) PLUS friction Monday, November 13th (marking period 1)!

### 🟩 5: M 11/6 - 📖 MP friction problems

Today, we'll finish going through the Friction PowerPoint if we haven't finished last time. Then, we'll work on on friction problems collaboratively. Work on problems from Chapter 5 in your textbook in 📖 Mastering Physics "Ch 5.5 - friction problems": #27, 29, 31, 32, 71, 73.

In addition, I would like for you to show all of your work on one problem which you will submit in person in class on Wednesday, November 8th. Your full solution should include:

At least 1 free body diagram, if not more.

Indicate sign convention.

State Newton's 2nd Law in equation form, indicating positive and negative forces. Do this vertically and horizontally.

State the known relationship between friction and normal force, and also the relationship between mass and force of gravity.

Manipulate with algebra to get the unknown variable in terms of known variables.

Plug in numbers to get a final numerical answer. Express all answers in 3 sig figs.

Not every part needs all of these, but make sure all of the above appear somewhere in your solution. You will be graded on your ability to communicate the solution clearly in addition to getting the correct numerical answer. Please make sure to stay in variable and only plug in numbers in the very last step.

THE QUESTION:

A 5kg block is placed on a rough surface initially at rest.

a) It takes 10 Newtons to get the block to start moving. What is the coefficient of static friction?

b) With the block initially at rest, what happens when a force of 8 N is applied to the block. Explain your reasoning.

c) Suppose a force greater than 10 N is applied to get the block to just start moving and after that, a force of 7 N is required to keep it moving at constant velocity. What is the coefficient of kinetic friction?

d) Suppose a force of 15 N is applied to the block. What is the acceleration of the block?

Optional Extra Practice: #11-17 on page 2 of Big Newton's Law Packet. SOLUTIONS to pp 1-2 of Packet.

Homework: Finish 📖 Mastering Physics by Tuesday, November 7th at 10pm. Also, submit your write up to the above problem at the beginning of class on Wednesday, November 8th. I recommend that you finish earlier (tonight) so that you can ask questions before the next quiz. Quiz on Newton's 2nd Law problems (including elevator problems) PLUS friction Monday, November 13th (marking period 1)!

### 💚 5: W 11/8 - Newton's 3rd Law

Today, we will start to explore Newton’s Third Law through interactive lecture and demonstrations. The law states, “If two bodies interact, the magnitude of the force exerted on object 1 by object 2 is equal to the magnitude of the force simultaneously exerted on object 2 by object 1, and these two forces are opposite in direction.” The important thing to remember is that action-reaction forces act on different objects!

Presentation: Newton's 3rd Law Presentation

Homework: Quiz on Newton's 2nd Law problems (including elevator problems) PLUS friction next class - Monday, November 13th (marking period 1)! Watch the following videos as a review of Newton's 3rd Law: