2. Aristotle 4 th Century Natural Motion Up or down Violent Motion Pushed or pulled 2.3 Newton’s 1 st Law

3. Nicholas Copernicus (Mikolaj Kopernik) 1473-1543 De Revolutionibus Earth goes around the Sun Feared Persecution 2.3 Newton’s 1 st Law

4. Galileo Galilei 1564-1642 Force is a push or pull Friction is the force between materials- caused by irregularities in surface Inertia 2.3 Newton’s 1 st Law Galileo explains his discoveries to the pope

5. Inertia Inertia (ih NUR shuh) is the tendency of an object to resist any change in its motion. 2.3 Motion and Forces It will keep moving at the same speed and in the same direction unless an unbalanced force acts on it.

6. Inertia The velocity of the object remains constant unless a force changes it. 2.3 Motion and Forces If an object is at rest, it tends to remain at rest. Its velocity is zero unless a force makes it move.

7. Galileo Galilei: Spheres on inclines 2.3 Newton’s 1 st Law Horizontal Surface: How High: Without Friction With Friction

8. Newton's Laws of Motion The British scientist Sir Isaac Newton (1642–1727) was able to state rules that describe the effects of forces on the motion of objects. 2.3 Motion and Forces These rules are known as Newton's law's of motion.

9. Newton's First Law of Motion Newton's first law of motion is that an object stays at rest or stays at a constant velocity unless acted upon by a net force 2.3 Motion and Forces This law is sometimes called the law of inertia. ( you might know this as an object at rest stays at rest, an object in motion stays in motion unless acted upon by an unbalanced force)

10. Newton's First Law of Motion Newton's first law of motion is that an object stays at rest or stays at a constant velocity unless acted upon by a net force 2.3 Motion and Forces Does this law pertain to moving objects, objects at rest or both?

11. Forces Push or pull Can be At-a-distance Contact 2.3 Motion and Forces

12. Unbalanced Forces 2.3 Motion and Forces The forces are considered to be unbalanced forces because the forces do not cancel each other perfectly.

13. Unbalanced Forces The students are pushing on the box in the same direction. 2.3 Motion and Forces These forces are combined, or added together, because they are exerted on the box in the same direction.

14. Balanced Forces The net force on the box is zero because the two forces cancel each other. Forces on an object that are equal in size and opposite in direction are called balanced forces. 2.3 Motion and Forces

15. Possible Motions 2.3 Motion and Forces What are the possible motions for an object with Unbalanced forcesBalanced Forces

16. Newton's First Law of Motion 2.3 Motion and Forces Demonstrations Table cloth http://www.stevespanglerscience.com/content/science-video/tablecloth-trick http://images.google.com/imgres?imgurl=http://www.boingboing.net/images/ricardocloth.jpg&imgrefurl=http://www.boing boing.net/2007/12/19/old-table-cloth- tric.html&usg=__wHCnH5iUI2NuMys86fXQ6wWUU4g=&h=200&w=296&sz=24&hl=en&start=6&tbnid=Y6wH3E H6oHOE-M:&tbnh=78&tbnw=116&prev=/images%3Fq%3Dtablecloth%2Btrick%26gbv%3D2%26hl%3Den Seatbelts http://www.youtube.com/watch?v=knCgF8K8xcY&feature=channel

17. 2.3 Question 1 A force is a push or pull. Forces, such as the force of the atmosphere against a person’s body, are not always noticeable. A force is a __________. Section Check Answer

18. 2.3 Question 2 When are forces on an object balanced? Section Check Answer When forces are equal in size and opposite in direction, they are balanced forces, and the net force is zero.

19. 2.3 Question 3 Inertia is __________. Section Check A. the tendency of an object to resist any change in its motion B. the tendency of an object to have a positive acceleration

20. 2.3 Section Check C. The tendency of an object to have a net force of zero. D. The tendency of an object to change in speed or direction.

21. 2.3 Answer Inertia is the tendency of an object to resist any change in its motion. An unbalanced force must act upon the object in order for its motion to change. Section Check

22. Newton’s second law of motion states that a net force results in an acceleration Newton’s Second Law 3.1 Newton’s Second Law

23. Unbalanced Forces net force is the combination of forces acting on an object F Newtons 3.1 Motion and Forces When two students are pushing with unequal forces in opposite directions, a net force occurs in the direction of the larger force.

24. Mass NOT Volume  IS  Number of atoms  Measured in kilograms  Related to inertia  M kg 3.1 Motion and Forces

25. Newton’s second law of motion states that an unbalanced force results in an acceleration Newton’s Second Law 3.1 Newton’s Second Law F net m a

26. Net Forces 3.1 Motion and Forces Large mass vs. Small mass

27. What is gravity? Gravity is an attractive force between any two objects that depends on the masses of the objects and the distance between them. 3.2 Gravity

28. The gravitational force exerted on an object is called the object’s weight. 3.2 Gravity Weight Symbol: W Unit : Newton

29. Mass  IS  Number of atoms  Measured in kilograms  Related to inertia  Symbol: M  Unit: kg 3.2 Motion and Forces

30. Close to Earth’s surface, the acceleration of a falling object in free fall is about 9.8 m/s 2. 3.2 Gravity Earth’s Gravitational Acceleration This acceleration is given the symbol g and is sometimes called the acceleration of gravity.

31. 3.2 Gravity Weight Because the weight of an object on Earth is equal to the force of Earth’s gravity on the object, weight can be calculated from this equation: W m g

32. The table shows how various weights on Earth would be different on the Moon and some of the planets. 3.2 Gravity Weight and Mass

33. What happens on the Moon if you drop a feather and hammer? http://er.jsc.nasa.gov/seh/feather.html 3.2 Gravity Hammer and Feather

34. 3.2 Gravity Weightlessness and Free Fall at 400-km altitude the force of Earth’s gravity is about 90 percent as strong as it is at Earth’s surface. So an astronaut with a mass of 80 kg still would weigh about 700 N in orbit, compared with a weight of about 780 N at Earth’s surface.

35. If you and the scale were in free fall, then you no longer would push down on the scale at all. 3.2 Gravity Floating in Space The scale dial would say you have zero weight, even though the force of gravity on you hasn’t changed.

36. The amount of air resistance on an object depends on the speed, size, and shape of the object. Air Resistance 3.1 Newton’s Second Law Air resistance, not the object’s mass, is why feathers, leaves, and pieces of paper fall more slowly than pennies, acorns, and apples.

37. As an object falls, the downward force of gravity causes the object to accelerate. Terminal Velocity 3.1 Newton’s Second Law However, as an object falls faster, the upward force of air resistance increases. This causes the net force on a sky diver to decrease as the sky diver falls.

38. The terminal velocity is the highest speed a falling object will reach. Terminal Velocity 3.1 Newton’s Second Law The terminal velocity depends on the size, shape, and mass of a falling object. Happens when Weight = air resistance

39. 3.1 Section Check Question 1 A. acceleration B. momentum C. speed D. velocity Newton’s second law of motion states that _________ of an object is in the same direction as the net force on the object.

40. 3.1 Section Check Answer The answer is A. Acceleration can be calculated by dividing the net force in newtons by the mass in kilograms.

41. 3.1 Section Check Question 2 A. joule B. lux C. newton D. watt The unit of force is __________.

42. 3.1 Section Check Answer The answer is C. One newton = 1 kg · m/s 2

43. 3.1 Section Check Answer Friction results from the sticking together of two surfaces that are in contact. Question 3 What causes friction?

44. 3.2 Gravity Centripetal Force An unbalanced force that cause a change in direction is a centripetal force.

45. Anything that moves in a circle is doing so because a centripetal force is accelerating it toward the center. 3.2 Gravity Centripetal Force and Traction

46. 3.2 Gravity Centripetal Force and Traction This centripetal force is the frictional force between the tires and the road surface. This centripetal force is the sides of the washer

47. Newton’s Third Law Newton’s third law of motion describes action-reaction pairs this way. When one object exerts a force on a second object, the second one exerts a force on the first that is equal in strength and opposite in direction. 3.3 The Third Law of Motion

48. Action and Reaction When a force is applied in nature, a reaction force occurs at the same time. When you jump on a trampoline, for example, you exert a downward force on the trampoline. 3.3 The Third Law of Motion Simultaneously, the trampoline exerts an equal force upward, sending you high into the air.

49. Action and Reaction Forces Don’t Cancel According to the third law of motion, action and reaction forces act on different objects. Thus, even though the forces are equal, they are not balanced because they act on different objects. 3.3 The Third Law of Motion

50. For example, a swimmer “acts” on the water, the “reaction” of the water pushes the swimmer forward. Thus, a net force, or unbalanced force, acts on the swimmer so a change in his or her motion occurs. 3.3 The Third Law of Motion Action and Reaction Forces Don’t Cancel

51. Rocket Propulsion In a rocket engine, burning fuel produces hot gases. The rocket engine exerts a force on these gases and causes them to escape out the back of the rocket. By Newton’s third law, the gases exert a force on the rocket and push it forward. 3.3 The Third Law of Motion

52. 3.3 Section Check Question 1 According to Newton’s law, the second object exerts a force on the first that is equal in strength and opposite in direction. According to Newton’s third law of motion, what happens when one object exerts a force on a second object? Answer

53. Force Pressure Area http://www.stevespanglerscience.com/content /science-video/the-can-crusherhttp://www.stevespanglerscience.com/content /science-video/the-can-crusher 3.3 The Third Law of Motion Pressure = Force/ Area F P A