Wednesday January 14

Hand-in Todays Homework Page 139 1-4 Page 144-145 23-29 We will look at friction, air resistance. Open book quiz. Review and in class problems on Friday Test on Monday

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

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

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

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

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

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

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

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

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

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

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

Section 4.4: Everyday Forces Holt Physics Chapter 4 Section 4 Pages 133-141

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

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

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

Everyday Forces Normal force diagrams-

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

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

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

* 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

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)

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

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.

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

The four fundamental forces of Physics https://www.youtube.com/watch?v=a-6skWBuHaE