INTRO VIDEO REVIEW QUIZ

Transcription

1 DEVIL PHYSICS BADDEST CLASS ON CAMPUS PRE-DP PHYSICS INTRO VIDEO Newton's Third Law of Motion REVIEW QUIZ 1. What is force? 2. Name Newton s First Law of Motion. 3. What is inertia? 4. What is the chemistry definition of mass and what is the physics definition of mass? 5. How does weight differ from mass? 6. Newton s Second Law of Motion is best described by an equation. What is that equation? 7. What does the in the above equation mean?

2 8. What is the SI unit for force and what is it composed of? 9. What is Newton s Third Law of Motion? REVIEW QUIZ Answers 1. What is force? Any kind of push or pull on an object 2. Name Newton s First Law of Motion. Every body continues in its state of rest or of uniform speed in a straight line unless acted on by a nonzero net force. Or A body at rest tends to remain at rest, and a body in motion tends to remain in motion. 3. What is inertia? The tendency of a body to maintain its state of rest or of uniform motion in a straight line. 4. What is the chemistry definition of mass and what is the physics definition of mass? Chemistry the amount of matter in an object Physics the measure of inertia of a body

3 5. How does weight differ from mass? Weight is a force equal to the mass of an object times the acceleration due to gravity acting on the object. 6. Newton s Second Law of Motion is best described by an equation. What is that equation? 7. What does the in the above equation mean? The vector sum of all forces. 8. What is the SI unit for force and what is it composed of? Newton (N), kg m/s 2 9. What is Newton s Third Law of Motion? Whenever one object exerts a force on a second object, the second exerts an equal and opposite force on the first. Or, For every action, there is an equal and opposite reaction. LESSON 4-7: Solving Problems with Newton s Laws: Vector Forces and Free-Body Diagrams

4 1. Transition. In the last lesson/chapter we learned: a) SC.912.P.12.3: Interpret and apply Newton's three laws of motion. High b) Know that the SI unit for force is the Newton (N) and that it is derived from the units kg m/s 2 2. Lesson Objectives. By the end of this class you should be able to: a) SC.912.P.12.3: Interpret and apply Newton's three laws of motion. High b) Use vector addition to find the net force on an object and relate it to the resultant acceleration. c) Draw free-body/force diagrams of an object or collection of objects. d) Use free-body/force diagrams to analyze forces on an object. e) Appreciate how pulleys can reduce the amount of force required to lift an object. Difference Between 4-1 to 4-6 and 4-7??? Forces Are Not Necessarily In The Same Direction!!! 3. Vector Forces and Free-Body Diagrams

5 a) Newton s Second Law,, says that the acceleration of an object is proportional to the net sum of the vector forces acting on the object. What will be the acceleration on the box below? 100 N 70 kg 100 N R 100 N 100 N

6 4. Free-Body Diagram or Force Diagram a) When solving these types of problems, it is extremely important to draw free-body diagram for each object and analyze the forces acting on that object. b) Free-body diagrams only show the forces acting on the object. c) When objects are in contact with each other, they will exert a reaction force on each other in equal and opposite directions F 21 m 1 g F T2 m 2 g 2 m 1 g

7 m 2 g m 1 g m T g F FT /2 F FT /2 d) Free-body/Force diagrams are especially helpful in seeing the advantages of using pulleys F T 100kg F T mg F T F T F T F T 100kg mg Problem Solving Process (Pg 91)

8 Example 4-9 A person exerts 40.0N of force by pulling a rope which is at a 30.0 angle to the horizontal on a box with a mass of 10.0kg. Calculate: a. the acceleration of the box b. the magnitude of the upward force exerted by the table on the box Process Step Illustration 1. Draw a sketch 40N 30 10kg 2. Draw a free-body diagram F N F V 10kg F H F W 3. Resolve vectors into components 40N 30 F V F H

9 4. Apply Newton s second law to each component direction separately F N 10kg F V F H F W Vertical Horizontal

10 5. Solve equations for unknowns Vertical Horizontal XX Period STOPPED HERE SUMMARY 1. Objectives. Are you able to: a) SC.912.P.12.3: Interpret and apply Newton's three laws of motion? High b) Use vector addition to find the net force on an object and relate it to the resultant acceleration?

11 c) Draw free-body/force diagrams of an object or collection of objects? d) Use free-body/force diagrams to analyze forces on an object? e) Appreciate how pulleys can reduce the amount of force required to lift an object?

12 LESSON 4-7: HOMEWORK Physics 1 Honors: #23-34