DAY 45
Goals: SWBAT...
1. Define the Friction Force.
2. Distinguish between static and kinetic friction
3. Solve friction problems
4. Find the coefficient of friction between objects in the classroom.
WARM-UP
1. Take the laminated "Paxton Patterson" Activity Reference book off your desk, close it, and lay it on it's back. Use one finger only, and Gently try to slide it across your desk. Then answer the following:
A. Which required a greater force, getting the book moving, or keeping it moving?
B. Think about the brief moment when you got the book moving - what happened right then that you could use as evidence to prove your answer in "A" above.
C. Draw a FBD showing the forces felt by the reference book.
D. Put the book away.
E. What tool could you use to prove your answer from part B?
CLASSWORK: (for each CW activity, think about which goal you are meeting. Also, which activity helps you achieve that goal?)
1. R.Q. (5min)
2. Kahoot
3. Friction Notes
a. Definition
b. Symbols
4. Students create an FBD model based on the following info:
- Scenario: A boy is exerting a 25-N horizontal force (to the right) on a 36-N box that's sliding at a constant velocity on a cement sidewalk. What is the coefficient of kinetic friction between the sidewalk and box?
- revise - how many forces are acting on the box?
- revise - are the x-forces in equilibrium? Yes or no? What does that mean for the magnitude (length) of your vector arrows? What about the y-forces?
5. Hands On Activity: Finding Ff Static and Kinetic (30min)
- You will be using the friction force and normal force to calculate the coefficient of static friction for multiple tubs of varying masses. A larger coefficient indicates a stronger friction force (AKA, a larger resistance to movement), and a smaller coefficient indicates a weaker friction force (AKA, a smaller resistance to movement)
- Which goal from above connects to this activity?
Instructions:
1. Record the tub number and mass of your tub in kg
2. Calibrate your spring scale to 0g.
3. Set up your system. Attach the spring scale to the hole on your tub. Move the tub to the end of the table.
4. Using the spring scale, apply a gentle pulling force to the tub. Record the maximum force you can apply WITHOUT the tub moving.
5. Repeat number 4 above, except this time get the tub to move at the slowest possible CONSTANT VELOCITY. Record the force
applied during the constant velocity phase.
6. Repeat steps 1-5 for a total of three tubs
7. Once you have data for three tubs, find the normal force of each tub, then find the coefficient of kinetic friction for each tub. Use the example on pg 128 if you get stuck.
Homework:
Read Example Problem #3, pg 128
Complete pg 128 17-21. For number 21, you'll need to use the data from the table on page 129.
Questions? Shoot me a message (preferred) on the Remind App, or email me j.alexander@tch.birminghamcharter.com.
Goals: SWBAT...
1. Explain why an object moving in a circle at a constant speed is accelerated.
2. Describe how centripetal acceleration depends upon the object’s speed and the radius of the circle.
3. Identify the force that causes centripetal acceleration.
WARM-UP & HW Check
1. Write the two equations for centripetal acceleration:
2. Use the ac equation that includes v and r to answer the following:
A. What happens to the magnitude of acceleration if the velocity increases?
B. Decreases?
C. What happens to the magnitude of acceleration if the radius increases?
D. Decreases?
3. You're in a car traveling on a straight freeway at a constant velocity of 70mph. The freeway curves to the right, and you turn the steering wheel right to follow the road.
A. Which way does the car go? (straight, right, or left)
B. Which way does the car accelerate?
C. Which way does your body go?
D. Which way does your body feel like it's accelerating?
E. Which way does your body want to go?
F. Why does your body go the direction it does?
CLASSWORK: (for each CW activity, think about which goal you are meeting. Also, tell me how the activity helps you achieve that goal)
1. 6.1 Quiz
2. Review W/U
3. HW Review
4. Practice: (Use Example Problem #2 (pg 155) as an example)
Solve pg 166 61-67
Answers & Hints:
61: a: 9.59m/s2 b: 5.90x103 N
62: 71m/s2 Fc = 5.0x102 N
63. a: towards center b: r=5.0cm: 0.61m/s2 r=10.0cm: _____m/s2 r=15.0cm: ______m/s2
c: _________ force between the _____ & ______ d: _____________
64: no hints...
65: hint: use Ff=μkFN and recall that FN = mg for a flat surface.
66: Hint: The sum of the forces in the "Y" equals zero, therefore Fg + Fc = 0
67: .....
HOMEWORK:
Homework for Wednesday:
Watch the following: http://www.flippingphysics.com/skateboarding.html
http://www.flippingphysics.com/introduction-to-relative-motion.html
If the velocity of the Prius was 11m/s North, and the velocity of the Minivan was 22m/s South, what would the vpm be? Show your work.
Read pg 157-158. Reading Quiz 6.3 on Wednesday
Solve pg 159 22-25 (these are pretty quick/easy)
Final Exams will be given back Wednesday, and Corrections will be due Monday
CH6 Test Friday 1/29
Bring: 1pg sheet notes; Equation Sheet. Pencil for Scantron Problems.