Welcome to Physics 100: Physics for Society

1. Welcome to Physics 100: Physics for Society Course website: http://faculty.wiu.edu/p-wang

2. Introduction to the syllabus • Word puzzle:Physics 100 is a GPA accelerator if and only if you P_ _ _ _ _ _ _ _ _ _. Answer: P A R T I C I P A T E.

3. Chapter 1 The Laws of Motion, Part 1 August 20: Skating−Newton’s first law of motion

4. Observations about the facts on skating: Movie: Ice skating −“Push … hold.” • When you’re at rest on a level surface, • without a push, you remain stationary. • with a push, you start moving to that direction. • When you’re moving on a level surface, • without a push, you coast steady and straight. • with a push, you change your direction or speed.

5. Question 1: Why does a stationary skater remain stationary? Demo: Tablecloth

6. Question 2: Why does a moving skater continue moving? Thought experiment: Galileo’s inclined planes

7. Physics concept: Inertia • A body at rest tends to remain at rest • A body in motion tends to remain in motion Newton’s first law of motion: (Start version) An object that is free of external influences moves in a straight line and covers equal distances in equal times. Note: A stationary object also obeys this law.

8. Question: • Why is Newton’s first law of motion not so apparent to us in our everyday life? • Real-world complications mask simple physics • Solution: minimize or overwhelm complications • To demonstrate inertia: • Work on level ground (minimize gravity influence) • Use wheels, ice, or air support (minimize friction) • Work fast (overwhelm friction) • Use vacuum (remove air resistance)

9. Read: Ch1: 1 Homework: Ch1: E(E means Exercise)3,6. Due: August 31

10. August 22: Skating − Newton’s second law of motion

11. Physical quantities: • Position– an object’s location Avectorquantity has magnitudeand direction. The magnitude of position is called distance. • Velocity – the change in position with time The magnitude of velocity is called speed. • Force – a push or a pull

12. Newton’s first law of motion: (Start version review) An object that is free of external influences moves in a straight line and covers equal distances in equal times. Now let us use physical terms: Newton’s first law of motion An object that is not subject to any outside forces moves at a constant velocity. Essence of Newton’s first law: There is no force needed in order to keep your velocity.

13. Questions: • How does a skater start or stop moving? • He needs a push or pull to start or stop. • How does a skater respond to a push? • He changes his velocity. • Do all skaters respond equally to equal pushes? • Kids respond more quickly than adults do.

14. More physical quantities: • Mass – measure of an object’s inertiaEverything has a mass. • Acceleration – change in velocity with time.Acceleration is a vector which has the same direction as the force causing it.Deceleration is actually a type of acceleration.

15. Examples of acceleration: • A car is getting into the highway. • A car is going to a stop sign. • A car is shifting to the left to pass another car. • An elevator is leaving the first floor. • A ball is dropping from a window. • A cart is running down an incline. • The moon is circling the earth. • However, an object that is stationary or has a constant velocity is not accelerating.

16. Net force – sum of all the individual forces exerted on an object. Relation between net force, mass and acceleration: Cause Effect Resistance or in algebra,

17. Newton’s second law of motion An object’s acceleration is equal to the net force exerted on it divided by its mass. That acceleration is in the same direction as the net force. Demo: Hammer, blocks, and hand

18. Question: You are given two black bottles, one empty and the other with water in it. How do you distinguish them without lifting them? Question: A 5-Newton (N) force is applied on a cart with 10-kilogram (kg) of mass. What is the acceleration of the cart? Answer:

19. Read: Ch1: 1 Homework: Ch1: E8;P(P means Problem)1 Due: August 31

20. August 24: Skating − Measurement and units

21. Newton’s second law of motion An object’s acceleration is equal to the net force exerted on it divided by its mass. That acceleration is in the same direction as the net force. Question: How do we calculate the net force if an object receives more than one forces? Answer: Because forces are vectors, we must find the net force using the rule of addition of vectors.

22. Vector addition: Vector subtraction:

23. Measurement and units: • The SI unit (Systéme Internationale d’Unités) has been adopted as the standard unit system in physics. The three basic SI units in mechanics:

24. Merits of the SI units: • Different units for the same quantity are related by factors of 10, 100, 1000, … • There are only a few basic units (meter, kilogram, second for mechanics). • Examples: SI units 1 kilometer = 1000 meter 1 meter = 100 centimeter = 1000 millimeter 1 kilogram = 1000 gram English units 1 mile = 5280 feet = 1760 yard 1 foot = 12 inch 1 pound = 16 ounce

25. Derived units:

26. The SI units and the English units:

27. How to change a unit: • Example: 65 mile/hour = ? meter/second Answer:

28. Question: Your mass is 80 kilogram and you are standing on ice. Your friend starts to push you with a force of 10 Newton. What is your acceleration? Answer:

29. Read: Ch1: 1 Homework: Ch1: E9;P2 Due: August 31

30. August 27: Falling Balls − Gravity

31. Absence policies • Students are expected to attend all classes. Absences, including tardy or early leaving, are not permitted unless preapproved or in emergency. Students are responsible for materials presented in class and for changes to the schedule or plans which are announced in class. • For absences due to prearranged university business, such as travel of athlete teams and military activities, appropriate document should be submitted in the beginning of the semester. • In case of emergency you can leave at any time, however an appropriate document for the nature of the emergency is required afterward. • Email the instructor before other planned absences. Your email should describe the event that prevents you from coming to the class. Usually you will get a quick reply from the instructor if the absence is excused. If otherwise it is not approved, a reason will be given in the reply. • Absences are monitored by non-preannounced in-class quizzes or sign-in sheets. • Filing WIU OARS (Online Absence Reporting System) is not automatically treated as an approved absence.

32. Observations about the facts on falling balls: • When you drop a ball, it • begins at rest, but acquires downward speed. • covers more and more distance each second. • When you toss a ball straight up, it • rises to a certain height and comes briefly to a stop. • begins to descend, like a dropped ball. • A thrown ball travels in an arc.

33. Question 1: Why does a dropped ball fall downward? Gravity and weight • Gravity is a physical phenomenon that exerts a force on the ball. This force is the ball’s weight. • The earth’s gravity produces the ball’s weight. The weight points toward the earth’s center. • The ball’s weight causes it to accelerate downward.

34. Question 2: Do different balls fall at different acceleration? Weight and mass • An object’s weight is always proportional to its mass. • Near the surface of the earth,whichis called the “acceleration due to gravity”. weight = mass · acceleration due to gravity in algebra (Demo using weights and a spring scale)

35. Acceleration due to gravity • Why is the name? • weight/mass = force/mass = acceleration • Acceleration due to gravity is indeed an acceleration. • 9.8 Newton/kilogram = 9.8 meter/second2 • On the surface of the earth, all falling balls accelerate downward at • Therefore different balls fall at the same acceleration.

36. Question: Dr. Wang’s mass is 76.5 kilogram. What is his weight on the earth? What is his weight in the far space? If he falls down from a cliff, What is his acceleration?

37. More about gravity: the law of universal gravitation gravitational Near the surface of the earth,

38. Acceleration due to gravity (g) varies: • At mountains • Shape of the earth: oblate spheroidAt the equator (r = 6378 km), at the poles (r = 6357 km) • At the moon • Dig a deep hole?

39. Read: Ch1: 2 Homework: Ch1: P9,10. Due: September 7

40. August 29: Falling Balls − Projectile motion

41. PHYSICS TUTORING CENTER (Especially for your homework) Fall 2018, Currens Hall 515 They are prepared to help you. ALL FREE!

42. The velocity of a falling ball Observation:A falling ball accelerates downward. Its acceleration is a constant. Its velocity increases in the downward direction. Question:How do we calculate the velocity of an object which has a constant acceleration? unknown in algebra,

43. The position of a falling ball Observation:A falling ball accelerates downward steadily. Its altitude decreases ever faster. Question:How do we calculate the position of an object which is accelerating constantly? If the acceleration is constant, we can use “average velocity  time” to find the change of position. in algebra,

44. The position and velocity of a ball falling from rest Velocity: “ ̶ ” means downward. Position:

45. The position and velocity of a ball thrown upward Velocity: Position:

46. Throwing a ball at an angle Simplification of physics: A vector can be separated into its horizontal and vertical components. The two components follow Newton’s laws of motion independently. • In the vertical direction, the ball is falling. It goes up initially at viy. • In the horizontal direction, the ball coasts at vix. Gravity only affects the ball’s vertical motion: Movie: Projectile motion

47. Question: A hunter is shooting at a monkey far away on a tree with a gun. If the monkey knows a little physics, when he sees the flash from the gun, should he 1) stay still on the tree, or 2) jump down from the tree?

48. Read: Ch1: 2 Homework: Ch1: P11,12,13. Due: September 7

49. August 31: Ramps − Newton’s third law of motion

50. Bonus on Answering In-class Questions • This form is downloadable from our course website. • Please raise your hand before answering an in-calss question. • Please briefly record your oral answers when you are called by the instructor. • Please submit this form before each exam to get a bonus. • You get a bonus even if your answers are not correct.