1. Wednesday January 14

2. Hand-in Todays Homework
Page
Page
We will look at friction, air resistance.
Open book quiz.
Review and in class problems on Friday
Test on Monday

3. Review: Newton’s Laws
Let’s review Newton’s three laws together

4. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? The relationship between an object's mass (m), its acceleration (a), and the applied force F is F=ma. Acceleration and force are vectors. This law requires that the direction of the acceleration vector is in the same direction as the force vector. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

5. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? For every action there is an equal and opposite reaction. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

6. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

7. Which of Newton's three laws does the following example illustrate
Which of Newton's three laws does the following example illustrate? If you have a hockey puck sliding along a table, it will eventually come to a stop. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

8. Which law states the need to wear seatbelts
Which law states the need to wear seatbelts? A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: none of the above

9. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? The relationship between an object's mass (m), its acceleration (a), and the applied force F is F=ma. Acceleration and force are vectors. This law requires that the direction of the acceleration vector is in the same direction as the force vector. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

10. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? For every action there is an equal and opposite reaction. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

11. Which of Newton's Three Laws does the following statement satisfy
Which of Newton's Three Laws does the following statement satisfy? Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

12. Which of Newton's three laws does the following example illustrate
Which of Newton's three laws does the following example illustrate? If you have a hockey puck sliding along a table, it will eventually come to a stop. A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: All of the above

13. Which law states the need to wear seatbelts
Which law states the need to wear seatbelts? A: Newton's First Law B: Newton's Second Law C: Newton's Third Law D: none of the above

14. Section 4.4: Everyday Forces
Holt Physics
Chapter 4 Section 4
Pages

15. Everyday Forces
Weight – the magnitude of the force of gravity acting on an object

16. Fg = mg * Mass ≠ Weight Everyday Forces
Fg = force due to gravity (in Newtons)
m = mass of object (in kilograms)
g = acceleration due to gravity (-9.81 m/s2)
* Mass ≠ Weight

17. Everyday Forces
Normal Force – (Fn) – a contact force exerted by one object on another in a direction perpendicular to the surface of contact. On a horizontal surface, Fn = mg

18. Everyday Forces
Normal force diagrams-

19. Everyday Forces
Frictional Forces – Contact forces which oppose applied forces
These are the surfaces in contact at a microscopic level.

20. Everyday Forces Static friction - (Fs) - force exerted
on a motionless object by the
environment to
resist an
external force
attempting to
cause a change
in motion

21. Everyday Forces Kinetic friction – (Fk) – force
exerted on a moving object that
opposes
motion

22. * Fk < Fs due to surface adhesion between two surfaces in contact
Coefficient of friction (μ) – a ratio of frictional force to normal force between two objects

23. Coefficient of Friction
The coefficient of friction is a ratio of force of friction to the normal force acting between two objects.
-This completely depends on the objects in contact.
-Different experimental values have been calculated based on the materials in contact (page 136: table 4-7)

24. Coefficient of Friction Equations
Coefficient of static friction
μs = Fs,max Fn
Coefficient of kinetic friction
μk = Fk

25. Sample problem
Page 145 #35
95Kg clock initially at rest on a horizontal floor requires 650N force to set it in motion.
After the clock is in motion, a force of 560N keeps it moving with a constant velocity.
Find the coefficient of static and kinetic friction between the clock and the floor.

26. Everyday Forces Air resistance is a form of friction  as velocity
increases so does
air resistance

27. The four fundamental forces of Physics