2. F = ma

3. When Making a sudden stop in your car, what pushes you into the seat belts? A. Nothing, your own motion does it B. Your seat C. Nothing, your seat belts just tighten D. The Force

4. “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

5. 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)

6. [Enter question here] 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 Which of the following is an example of a force?

7.  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

8. 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)

9. 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

10. [Enter question here] A.Gravitational Force B.Electric Force C.Frictional Force D.Magnetic Force E.THE Force 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?

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 net force. An object in motion will stay in motion unless acted upon by an outside net 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. [Enter question here] 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. Which of these objects has the greatest amount of inertia?

17. [Enter question here] A.Slow to a stop B.Travel in a parabola C.Continue in a straight line. D.Maintain constant speed. E.Both A and B F.Both C and D G.All of the above You pay a large amount of money to be sent to outer space. You finally reach a point where all the gravitational forces acting on you are close to zero. If you are traveling at the speed of light and then run out of fuel you will…..

18. 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?

19. [Enter question here] 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. What if… The net force acting on an object is zero?

20. I have a mass attached to the ceiling by a thread. There is also a thread attached at the bottom. If you pull the bottom string which will break first? A. Both at the same time B. The top one C. The bottom one D. Depends on how hard you pull it

21. 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!!!

22. 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...

23. Weight Find your weight on different places! Find your weight on different places! 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

24. [Enter question here] A.5.8 N B.58 N C.588 N D.5880 N E.60 kg F.None of the above What is the weight of a 60 kg person on earth?

25. [Enter question here] A.1 N B.10 N C.100 N D.1000 N E.1.67 N What is the weight of a 60 kg person on the moon? (g m = 1.67 m/s 2 )

26. Constant acceleration from gravity Galileo found that balls of different masses fell at the same rate. Galileo found that balls of different masses fell at the same rate. The force of gravity is stronger for more massive objects. The force of gravity is stronger for more massive objects. But it requires more force to accelerate a more massive object (inertia). But it requires more force to accelerate a more massive object (inertia). These two effects cancel each other out. These two effects cancel each other out.

27. 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

28. 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).

29. 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

30. 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

31. 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. :)

32. 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.

33. 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

34. What is the mass of a 294 N box A. 30 kg B. 2880 kg C. 294 N D. 66 lbs

35. 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.

36. 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!

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

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

39. 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.

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

41. 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?

42. 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?

43. 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?

44. 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.

45. The mass of a refrigerator that slides across a kitchen floor that has a µ of 0.245 and an applied frictional force of 300 N. A. 125 kg B. 1220 kg C. 73.5 kg D. 7.50 kg

46. Basic Info: balanced Forces Objects are balanced only if their net force is zero in both the vertical and horizontal directions Objects are balanced only if their net force is zero in both the vertical and horizontal directions Meaning all the forces in the x direction add up to zero AND all the forces in the y direction add up to zero Meaning all the forces in the x direction add up to zero AND all the forces in the y direction add up to zero All forces that act in a angle needs to be broken into components using trig. All forces that act in a angle needs to be broken into components using trig. Meaning using a right triangle with x and y components. Meaning using a right triangle with x and y components.

47. Vector Components In order to find the components of a vector (like force) you will need to use those timeless Trigonometric Functions. In order to find the components of a vector (like force) you will need to use those timeless Trigonometric Functions.

48. Vector Components So we have a person pulling a sled 30 o with respect to the horizontal at a force of 50 N. So we have a person pulling a sled 30 o with respect to the horizontal at a force of 50 N. We need to think of it like the sled being pulled vertically and horizontally at the same time, giving it both components. We need to think of it like the sled being pulled vertically and horizontally at the same time, giving it both components. Θ =30 o F=50N FyFy FxFx

49. Vector Components In order to calculate the components, we need to shift F y to make a right triangle. In order to calculate the components, we need to shift F y to make a right triangle. Then we can use trig functions to solve for F y and F x like they are sides of a right triangle. Then we can use trig functions to solve for F y and F x like they are sides of a right triangle. To solve for F x, we will use cosine because it is adjacent and we have the hypotenuse. To solve for F x, we will use cosine because it is adjacent and we have the hypotenuse. Θ =30 o F=50N FyFy FxFx

50. Vector Components To solve for v x, we will use cosine because it is the adjacent side and we have the hypotenuse. To solve for v x, we will use cosine because it is the adjacent side and we have the hypotenuse. To solve for v y, use the same process but with sine. To solve for v y, use the same process but with sine. Θ =30 o F=50m/s FyFy FxFx

51. F y equals? A. 43.3 N B. 25 N C. 28.9 N D. 50 N Θ =30 o F=50m/s FyFy

52. FBD Example 1 A 50 kg mass is suspended from two wires, as in the diagram below. What is the tension in the wires?

53. FBD Example 2 A 25.0 N picture is hanging from two wires. The wires make a 30˚ angle with the top of the picture. Calculate the tensional force on each wire.

54. A force of 60 N is applied to a rope to pull a sled across a horizontal surface at a constant velocity. The rope is at an angle of 30 above the horizontal. Calculate the magnitude of the component of the 60N force that is parallel to the horizontal surface. A. 60 N B. 30 N C. 52 N D. 35 N

55. A force of 60 N is applied to a rope to pull a sled across a horizontal surface at a constant velocity. The rope is at an angle of 30 above the horizontal. Determine the magnitude of the frictional force. A. 60 N B. 30 N C. 52 N D. 18 N

56. How to draw a free-body diagram for an object on a ramp?

57. FBD example 3 A 20.0 kg block rests on a frictionless ramp, as in the diagram below. What is the tension in the string holding the block in place?

58. Formulas! 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

59. What is the coefficient of friction of a 30 kg box being pushed across a table in a constant speed with an applied force of 250 N. A. 1.176 B..12 C..850 D. 8.3

60. Even though the force of gravity on a less massive object is smaller, it still fall at the same rate as more massive objects because: Even though the force of gravity on a less massive object is smaller, it still fall at the same rate as more massive objects because: A. Air is pushing it down more. B. Because it has less resistance to changing it motion (inertia). C. Because it has more resistance to changing it motion (inertia). D. Magic

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

63. 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

64. 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?

65. 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!!

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