2. F = ma

3. “The Force” “An energy field created by all living things. It surrounds us, penetrates us, and binds the galaxy together.” “An energy field created by all living things. It surrounds us, penetrates us, and binds the galaxy together.” The Force has two components: The Force has two components: Light side Light side Dark side Dark side

4. The Real Force Something that causes an object’s motion to change (causes acceleration). Something that causes an object’s motion to change (causes acceleration). A “push” or a “pull.” A “push” or a “pull.” Common Examples of forces: Gravity fields, pushing on something, compressing a spring, a magnetic field, tension, friction, and the “normal” force. Common Examples of forces: Gravity fields, pushing on something, compressing a spring, a magnetic field, tension, friction, and the “normal” force. Units are Newtons (N) Units are Newtons (N)

5. Which of the following is an example of a force? a)Your weight b)A magnet pulling on another magnet c)A bully pushing you down the stairs d)A rope pulling a cartful of turnips e)All of the above f)None of the above

6.  Types of  Forces FieldFieldField Balloon bending stream of waterBalloon bending stream of water Projectile MotionProjectile Motion Magnetic fieldsMagnetic fields Contact Contact Me slapping you upside the head Me slapping you upside the head Baseball bat on a baseball Baseball bat on a baseball

7. Easily forgotten Forces!! Easily forgotten Forces!! Important contact force: FRICTION Acts in the opposite direction of motion Acts in the opposite direction of motion Produces HEAT Produces HEAT AIR RESISTANCE is a form of FRICTION!! AIR RESISTANCE is a form of FRICTION!! SLOWS MOTION SLOWS MOTION Can be desired (tires on road) or undesired (skates on ice) Can be desired (tires on road) or undesired (skates on ice)

8. Easily forgotten forces!! Important field forces: GRAVITY and Magnetic Fields Opperate at a distance (don’t need to “touch”) Opperate at a distance (don’t need to “touch”) Decreases with the distance between objects. Decreases with the distance between objects. WEIGHT is a FORCE caused by gravity WEIGHT is a FORCE caused by gravity F weight = mass x gravity F weight = mass x gravity As gravity changes, WEIGHT changes, NOT MASS As gravity changes, WEIGHT changes, NOT MASS

9. As a meteor passes the earth our gravity causes its path to bend. Another meteor passes us and its path is not bent nearly as much. Which meteor is closer to the earth? a)The first meteor b)The second meteor c)What meteor? d)Yes

10. So I’m cruising around Belton in my awesome car when I see a dog in the middle of the road! What is the main force that lets me stop my car so the doggy can live? a)Gravitational Force b)Electric Force c)Frictional Force d)Magnetic Force e)THE Force

11. Force is a vector Has magnitude and direction Has magnitude and direction Amount of force makes a difference Amount of force makes a difference Little push vs. big shove Little push vs. big shove Earth gravity vs. moon gravity Earth gravity vs. moon gravity Direction makes a difference Direction makes a difference Push vs. Pull Push vs. Pull Thrust vs. Drag Thrust vs. Drag Forces “add” to give a net force. Forces “add” to give a net force. Net force determines what an object will do. Net force determines what an object will do.

12. The law of inertia: An object at rest will stay at rest unless acted upon by an outside force. An object in motion will stay in motion unless acted upon by an outside force.

14. Galileo’s Unique Idea Objects don’t need a force to keep moving! Objects don’t need a force to keep moving! Every object naturally wants to maintain its state of motion or rest Every object naturally wants to maintain its state of motion or rest INERTIA! (resistance to change in motion) INERTIA! (resistance to change in motion) Refined by Newton in 1800’s: Refined by Newton in 1800’s:

15. Basic Info: Inertia Inertia depends on: Inertia depends on: Mass Mass Shape/Mass Distribution of object- rotational inertia Shape/Mass Distribution of object- rotational inertia Solid Cylinder (like a wheel of cheese,) Solid Cylinder (like a wheel of cheese,) Hoop (like a bicycle tire) Hoop (like a bicycle tire) Inertia does NOT depend on: Inertia does NOT depend on: Velocity/Speed of object Velocity/Speed of object It takes the same amount of force to speed a bus up as to slow it down! It takes the same amount of force to speed a bus up as to slow it down!

16. Which of these objects has the greatest amount of inertia? a) A 0.5 mg cockroach. b) A 2.0 g lump of cheese. c) A 35 g ball of goo. d) A 15 kg baby goat e) A 300 kg circus freak on roller skates.

17. Net Force Net Income: How much money did you make after you counted up all profit and expense? Net Income: How much money did you make after you counted up all profit and expense? Net Force: How much force is there after all individual forces are added up? Net Force: How much force is there after all individual forces are added up?

18. What if… The net force acting on an object is zero? a) The object will slow to a stop. b) The object will begin to fall. c) The object’s motion will not change. d) The universe will open up and swallow the object. e) Time will stop for us but the object will grow old and smelly.

19. Fun Stuff Wear your seatbelt! Wear your seatbelt! Wear your seatbelt! Wear your seatbelt! Fun stuff Fun stuff Other one Other one Other one Other one

20. In other words…  You already know this! the important part is the Σ. This means “Sum” or “Net”

21. Net Force Net Income: How much money did you make after you counted up all profit and expense? Net Income: How much money did you make after you counted up all profit and expense? Net Force: How much force is there after all individual forces are added up? Net Force: How much force is there after all individual forces are added up?

22. MassAcceleration X

23. Typical Situations Which is easier to accelerate? Which is easier to accelerate? A tiny sports car? Or a ridiculously large and completely unnecessary SUV? A tiny sports car? Or a ridiculously large and completely unnecessary SUV? Your car has stalled in the middle of the road! Your car has stalled in the middle of the road! Easier to push it to the side by yourself? Or with friends? Easier to push it to the side by yourself? Or with friends? More mass requires more Force!

24. Don’t forget the Force Causes accelerations Causes accelerations Gravity leads to: Projectile Motion, and more projectile motion Gravity leads to: Projectile Motion, and more projectile motion “Pushes and Pulls” can also cause accelerations (like this). “Pushes and Pulls” can also cause accelerations (like this). Measured in Newtons (N) Measured in Newtons (N) The amount of force that causes a 1 kg mass to accelerate at 1 m/s 2 The amount of force that causes a 1 kg mass to accelerate at 1 m/s 2

25. Always make sure your mass is in kilograms (kg)! Force (N) = mass (kg) x acceleration (m/s 2 )

26. Calculate the following 1. 1. What force is required to push your 1,100 kg car with an acceleration of 0.5 m/s 2 ?

27. Calculate the following 2. 2. If a 10 N force is applied to an object that causes it to accelerate at 22 m/s 2, what is the mass of the object?

28. Calculate the following 3. 3. The net force on the propeller of a 3.2 kg model airplane is 7.0 N forward. What is the acceleration of the airplane?

29. Calculate the following 4. 4. A force is applied to a 1.5 kg ball that causes it to accelerate from rest to a velocity of 4.5 m/s in 0.5 seconds. What is the magnitude of the force? Remember: F net = ma and a = (V f -V i )/t

30. Calculate the following 5. 5. A 12 kg box starts from rest and slides down a frictionless ramp. If the gravitational force pulling it down the ramp is 35 N, what is the final velocity of the box after 3.4 seconds?

31. For every action force there is an equal and opposite reaction force!!

32. These Two forces are known as an action/reaction pair.These Two forces are known as an action/reaction pair. Gravity acts on an object and the object acts with equal force.Gravity acts on an object and the object acts with equal force.

33. Newton’s Third Law Action-Reaction Pairs Action-Reaction Pairs The hammer exerts a force on the nail to the right. The hammer exerts a force on the nail to the right. The nail exerts an equal but opposite force on the hammer to the left. The nail exerts an equal but opposite force on the hammer to the left.

34.  The simplest example: If the girl pushes on the boy which one of them will move? Which one will have a greater acceleration?

35. Gravity “Gravitational Force” Force which is exerted by any object with mass. Force which is exerted by any object with mass. Earth’s gravitational force is measured as F g = mg, g = 9.8m/s 2 Earth’s gravitational force is measured as F g = mg, g = 9.8m/s 2 Direction is always down Direction is always down Designated F g Designated F g sometimes called weight sometimes called weight

36. Gravitational Force Newton’s Law of Universal Gravitation Newton’s Law of Universal Gravitation The amount of force is directly proportional to the mass of each of the objects. The amount of force is directly proportional to the mass of each of the objects. The gravitational force between two objects decreases as the distance between them (r) increases! This is an inversely proportional relationship! The gravitational force between two objects decreases as the distance between them (r) increases! This is an inversely proportional relationship! Don’t worry, we wont be using this equation yet! Don’t worry, we wont be using this equation yet!

37. The amount of gravitational force exerted on an object The amount of gravitational force exerted on an object 1 lb = 4.448 N1 N = 0.225 lb 1 lb = 4.448 N1 N = 0.225 lb MASS always the same (kg) WEIGHT depends on gravity (N) F W = mg F W (also W or F g ): weight (N) m:mass (kg) g:acceleration due to gravity (m/s 2 ) Weight and mass are two completely different things!!!

38. Would you weigh more on Earth or Jupiter? Would you weigh more on Earth or Jupiter? greater gravity greater weight greater mass Jupiter because... Jupiter because...

39. Weight Find your weight on different planets! Find your weight on different planets! First, find your mass in kilograms: take your weight and divide it by 2.2 (because 1 kg weighs 2.2 lbs) First, find your mass in kilograms: take your weight and divide it by 2.2 (because 1 kg weighs 2.2 lbs) Now, to find how many Newtons you weigh, take your mass (m) and multiply it by the gravitational acceleration (g). Remember: F=ma, or F W = mg Now, to find how many Newtons you weigh, take your mass (m) and multiply it by the gravitational acceleration (g). Remember: F=ma, or F W = mg g earth : 9.8 m/s 2 g earth : 9.8 m/s 2 g moon : 1.67 m/s 2 g moon : 1.67 m/s 2 g mars : 3.7 m/s 2 g mars : 3.7 m/s 2 g sun : 274.13 m/s 2 g sun : 274.13 m/s 2 g pluto : 0.42m/s 2 g pluto : 0.42m/s 2 To convert Newtons to Pounds, remember: 1 lb = 4.448 N To convert Newtons to Pounds, remember: 1 lb = 4.448 N

40. What is the weight of a 60 kg person on earth? a)5.8 N b)58 N c)588 N d)5880 N e)60 kg f)None of the above

41. What is the weight of a 60 kg person on the moon? (g m = 1.67 m/s 2 ) a)1 N b)10 N c)100 N d)1000 N e)1.67 N

42. Force of Normal The force that a surface exerts on an object. The force that a surface exerts on an object. Force is always in a direction perpendicular to the surface the object or system is in contact with Force is always in a direction perpendicular to the surface the object or system is in contact with Usually a balancing force when an object is in contact with another object Usually a balancing force when an object is in contact with another object Designated F N or N Designated F N or N

43. Force of Normal - Example Let’s say the box in this diagram has a mass of 25 kg. Let’s say the box in this diagram has a mass of 25 kg. That means it has a weight of 245 N. That means it has a weight of 245 N. Since the ground is level, the Normal Force is going to be equal to the box’s weight, but the force is exerted in a different direction (up). Since the ground is level, the Normal Force is going to be equal to the box’s weight, but the force is exerted in a different direction (up).

44. Force of Normal - Example 2 That last one was easy! Let’s say this box is seated on an incline and still has a mass of 25 kg. That last one was easy! Let’s say this box is seated on an incline and still has a mass of 25 kg. The weight of the box (mg) is still directed straight down, but the Normal Force is at an angle, which makes it a little harder to find… The weight of the box (mg) is still directed straight down, but the Normal Force is at an angle, which makes it a little harder to find… F N = wcosθ F N = wcosθ

45. Force of Friction Static Friction is the force which keeps an object stationary Static Friction is the force which keeps an object stationary Kinetic Friction slows an object in motion Kinetic Friction slows an object in motion Force is dependent on surface type and pressure pushing the two objects together Force is dependent on surface type and pressure pushing the two objects together F f =  F N F f =  F N  is the coefficient of friction, and describes the “roughness” of a surface.  is the coefficient of friction, and describes the “roughness” of a surface. Force is directed opposite motion or expected motion Force is directed opposite motion or expected motion

46. Find the Force of Friction… For a 5 kg box that is being pushed across a table which has a µ of 0.655. :) For a 5 kg box that is being pushed across a table which has a µ of 0.655. :)

47. Find the Force of Friction… For the shoes of a 60 kg student as they walk across a floor with a µ of 0.654. For the shoes of a 60 kg student as they walk across a floor with a µ of 0.654.

48. Tension Force applied by a string or cable when the object or system is hanging Force applied by a string or cable when the object or system is hanging Direction can be variable Direction can be variable A force of tension is described as F T or T A force of tension is described as F T or T

49. Basic Info: Force Diagrams Definition: A Diagram that shows all the forces acting on a body Definition: A Diagram that shows all the forces acting on a body Does NOT include forces exerted by the body! Does NOT include forces exerted by the body! Forces are drawn as vectors. Forces are drawn as vectors.

50. Free Body Diagram Simple drawing of all forces working on an object or system Simple drawing of all forces working on an object or system Use a box to represent the object or system Use a box to represent the object or system All forces move away from the box. All forces move away from the box. Remember: gravity will always affect an object and so Fg will always be in a F.B.D! Remember: gravity will always affect an object and so Fg will always be in a F.B.D!

51. Diagram the forces acting on a car stuck in a traffic jam. Diagram the forces acting on a car stuck in a traffic jam.

52. Diagram the forces acting on a car driving on IH-35. Diagram the forces acting on a car driving on IH-35.

53. Basic Info: Unbalanced Forces Objects that are NOT in equilibrium Objects that are NOT in equilibrium Will accelerate! Will accelerate! Objects in equilibrium will not accelerate (inertia) Objects in equilibrium will not accelerate (inertia) Net force required to speed up, slow down, turn, etc. Net force required to speed up, slow down, turn, etc. Demos: Demos: Frictionless Track at an angle- Remember Forces are Vectors and can have 2 components!! Frictionless Track at an angle- Remember Forces are Vectors and can have 2 components!!

54. Which of these situations shows balanced forces? Which will accelerate? AB C D: all of them E: none of them

55. 1. As a 1150 kg car is driving on the highway the engine is supplying a force of 900 N. The total force of friction (including air resistance and the internal friction of the engine) is 460 N. What is the net force on the car in the direction of motion?

56. 2. A 5 kg box slides across a table that has a coefficient of friction of 0.236. If the force applied to the box is 25 N, what is the net force acting on the box in the direction of motion?

57. 3. A force of 150 N is applied to a 15 kg wood block to make it slide across a piece of sandpaper. a) What is the force of normal acting on the wood block? b) What is the force of friction acting on the wood block if the μ of the sandpaper is 0.995? c) What is the net force acting on the wood block? d) What is the acceleration of the block?

58. 4. A 8 kg block of cheese is sitting on a ramp with a 30 o incline and a µ of 0.745. Draw a force diagram showing all the forces acting on the cheese.

59. Formulas! Fnet = ma Fnet = ma W = mg W = mg F f = μF N F f = μF N F net = F A – F f F net = F A – F f Object on a flat surface: Object on a flat surface: F N = Weight F N = Weight Object on an incline: Object on an incline: F N = Wcosθ F N = Wcosθ F A = Wsinθ F A = Wsinθ

61. Car Collision More than one Object = more than one diagram Forces exerted on car Forces exerted on wall

62. Here is a force diagram for a car travelling on the highway. Is the car speeding up? If the driver takes his foot off of the gas what force causes him to slow down? A B C D D: all of them E: none of them

63. Key Term: Equilibrium When Net Force = 0 When Net Force = 0 Acceleration = 0 Acceleration = 0 Velocity doesn’t change Velocity doesn’t change could be moving! could be moving! could be sitting still! could be sitting still! Can an object be in equilibrium if only one force acts upon it?

64. Rocket exerts a downward force on the Gasses in its combustion chamber. The ground/gases exert an equal and opposite force that propels the rocket up Student question: But wait!! Don’t these forces look balanced?!? Why does the rocket accelerate?!? Mr. Jehl’s answer: You are exactly right!! The tricky part is that this picture doesn’t show an accurate force diagram!! A good diagram only shows Forces acting ON an object!!!! Let’s fix it!!

65. Watch these videos, then see how many examples of newton’s laws you can you find?