If there is nothing pushing on an object, it will not move. If there is nothing pushing on an object, it will not stop. The List:

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2 If there is nothing pushing on an object, it will not move. If there is nothing pushing on an object, it will not stop. The List: No Push No Go No Push No Stop No Push No Speed Up No Push No Slow Down No Push No Turn

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4 a force always acts in a certain direction ex. if you push something, the force is in the direction of the push

5 What different types of forces are there? Force of Gravity Force of Friction Air Resistance Normal Force

6 The first person to realize the relationship was Sir Isaac Newton

7 An object at rest will stay at rest, and an object in motion will stay in motion at constant velocity, unless acted upon by an unbalanced force.

8 Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless. These pumpkins will not move unless acted on by an unbalanced force.

9 Once airborne, unless acted on by an unbalanced force (gravity and air fluid friction), it would never stop!

10 Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

11 Another way to think about it: If you are in a car at a stop light, and the driver speeds up really fast, where do you tend to go? If you are driving and come to a quick stop, which way do you tend to go? If you spin a bucket on a rope, in what direction will the bucket go if the line is cut?

12 What is a force? This is the push or pull on an object that either gets the object moving, makes it stop, or makes it turn. It is measured in the units of Newtons (N) What does unbalanced mean? This means that, if you add all the pushes and pulls together, there is a overall push/pull in one direction

13 When we look at forces, we will break them into forces working in the same plane. This means all vertical forces can be added and all horizontal forces can be added Which forces can be added together in the diagram? D) 10 N A) 10 N C) 10 N B) 10 N

14 What happens if the forces do not add to 0? These are unbalanced forces, and this creates an acceleration in the object. What is the size of the unbalanced force? D) 10 N A) 10 N C) 10 N B) 40 N

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16 When you are performing calculations, you should always look at a drawing of the situation. We do this using an FBD or Free body diagram An FBD uses arrows to describe the forces acting on the body and in which direction.

17 10 N 10 N 10 N 5 N This is an FBD of a situation. You need to resolve the forces into their x and y components If there are forces in the same plane, they can be added and subtracted from each other In this example, F y = 0, and F x = -5N or 5N [W]

18 What happens if the forces are not in just the x or y? Break each force into an x and a y component, then find the sum. This is done using trigonometry (sine and cosine).

19 Net force (resultant force): a vector produced when 2 or more forces act on a single object. Calculated by adding the force vectors together. Also described as the overall force acting on an object

20 What different things can you think of that will affect how fast an object will accelerate? How hard the object is pushed (force) the bigger the force the bigger the acceleration How much mass the object has NOT ITS WEIGHT

21 Mass The amount of matter that is in an object. This amount never changes, no matter where you are. It is measured in kilograms (kg) Weight This value changes depending on where you are. It is a force, so it is measured in Newtons (N)

22 Don t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 m/hour.

23 No, he also came up with the following The rate of change in an objects velocity (acceleration) in directly proportional to the force applied, and inversely proportional to the mass of the object. This is called Newton s Second Law.

24 The net force of an object is equal to the product of its mass and acceleration, or F=ma.

25 Newton also gave us a formula that allows us to calculate the force being applied to an object F = ma Where: F is the force m is the mass of the object a is the acceleration of the object

26 When mass is in kilograms and acceleration is in m/s/s, the unit of force is in newtons (N). One newton is equal to the force required to accelerate one kilogram of mass at one meter/second/second.

27 How much force is needed to accelerate a 1400 kilogram car 2 meters per second/per second? Write the formula F = m x a Fill in given numbers and units F = 1400 kg x 2 meters per second/second Solve for the unknown 2800 kg-meters/second/second or 2800 N

28 If mass remains constant, doubling the acceleration, doubles the force. If force remains constant, doubling the mass, halves the acceleration.

29 We know that objects with different masses accelerate to the ground at the same rate. However, because of the 2 nd Law we know that they don t hit the ground with the same force. F = ma 98 N = 10 kg x 9.8 m/s/s F = ma 9.8 N = 1 kg x 9.8 m/s/s

30 1. What acceleration will result when a 12 N net force applied to a 3 kg object? A 6 kg object? 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec?

31 1. What acceleration will result when a 12 N net force applied to a 3 kg object? 12 N = 3 kg x 4 m/s/s 2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s 2. Determine the mass. 16 N = 3.2 kg x 5 m/s/s 3. How much force is needed to accelerate a 66 kg skier 1 m/sec/sec? 66 kg-m/sec/sec or 66 N 4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec/sec? 9800 kg-m/sec/sec or 9800 N

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33 Calculate the force on a 12 kg object if it accelerates at 3.4 m/s 2? F = m a F = (12 kg)(3.4 m/s 2 ) F = 40.8 N F = 41 N (sig figs) Calculate the acceleration of a 1.79x10 3 N force acting on a 743 kg object. F = m a a = F/m a = 1.79x10 3 N/743 kg A = 2.41 m/s 2

34 For every action, there is an equal and opposite reaction.

35 According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.

36 There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces.

37 Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. In turn, the water reacts by pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards).

38 Flying gracefully through the air, birds depend on Newton s third law of motion. As the birds push down on the air with their wings, the air pushes their wings up and gives them lift.

39 Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. In turn, the air reacts by pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). Action-reaction force pairs make it possible for birds to fly.

40 The baseball forces the bat to the left (an action); the bat forces the ball to the right (the reaction).

41 Consider the motion of a car on the way to school. A car is equipped with wheels which spin backwards. As the wheels spin backwards, they grip the road and push the road backwards.

42 The reaction of a rocket is an application of the third law of motion. Various fuels are burned in the engine, producing hot gases. The hot gases push against the inside tube of the rocket and escape out the bottom of the tube. As the gases move downward, the rocket moves in the opposite direction.

43 So long as the forces are balanced on an object, is there motion? The answer is YES, but why is this true? N2L says that there needs to be an unbalanced force to have an acceleration, NOT motion Be careful how you interpret the law!!

44 force of attraction between all objects in the universe the larger an object s mass, the greater the gravitational force

45 the greater the distance between two objects, the smaller the gravitational force the force of gravity decreases by the amount equal to one divided by the distance (d) squared 1/d 2

46 Using his own laws, Newton created a Universal Law of Gravitation that applies to everything in the Universe. Every particle attracts every other particle with a force that is proportional to the square of the distance between them.

47 If you perform unit analysis on the previous formula, you will find that they do not match, something is missing, they are not the units of force. It wasn t until Cavendish worked on it, that the constant was found, and the equation can be used. The constant was called the Gravitational Constant, G.

48 This lead the formula to change to the following: Example: Calculate the force of gravitational attraction between a 2.00 kg mass and a 5.00 kg mass separated by a distance of 3.00 m.

49 Ever had butterflies in your stomach if you moved really fast up or down on an elevator? What do you think happens to the weight the floor of the elevator sees as you move up or down? Does the weight stay the same, get bigger or smaller?

50 If you stand on an scale that measures Newtons in an elevator the following will happen Stopped or constant velocity: you will read your weight Moving up with an acceleration: the scale will read a larger weight (you feel heavier) Moving down with an acceleration: the scale will read a smaller weight (you feel lighter)

51 How do we prove these using calculations? Moving up: W = F g + F a Moving down: W = F g F a

52 Moving up: your weight seems to shift down and you feel heavier. You are experiencing added weight due to the acceleration of the elevator upwards Moving down: you feel a little lighter because you are experiencing a loss of weight due to the downward acceleration. Are there any exceptions you can think of?

53 What happens to your weight on the scale if the cable is cut? Are you accelerating at the same rate as that of gravity?

54 Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force? It s a force we sometimes cannot see friction.

55 Objects on earth, unlike the frictionless space the moon travels through, are under the influence of friction.

56 What is this unbalanced force that acts on an object in motion? There are four main types of friction: Sliding friction: ice skating Rolling friction: bowling Fluid friction (air or liquid): air or water resistance Static friction: initial friction when moving an object

57 Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of the presence of a force - that force being the force of friction - which brings the book to a rest position.

58 In the absence of a force of friction, the book would continue in motion with the same speed and direction - forever! (Or at least to the end of the table top.)

59 Friction force that opposes the motion of an object the force of friction works in the opposite direction of the force of motion

60 Sliding Friction the source of friction is the contact between two surfaces, at least one of which is in motion

61 Air Resistance friction results from air pushing on an object as it is moving

62 Rolling Friction friction between two surfaces that are not in constant contact ex. wheels

63 friction makes motion possible friction also makes it hard to move objects reducing friction makes it easier to move objects

64 by changing sliding friction into rolling friction by using lubricants Lubricants substances that reduce friction

65 We have all talked about friction, but what is it really? Friction is the force between objects in contact and parallel to contact surfaces There are 2 types of friction Static the friction where surfaces are stationary (book on a desk). Kinetic the friction between 2 surfaces that are in motion (tires on pavement)

66 There are different types of kinetic friction, and each have their own name depending on the situation Sliding friction affects sleds Rolling friction affects cars, bicycles etc. Fluid friction affects a boat moving through the water or a plane through the air Surface area does not affect friction

67 We can calculate the force of friction acting on an object. F f = mf N Where: F f = Force of Friction m s or m k = Coefficient of Friction (static or Kinetic) F N = Normal Force (the force applied at a right angle to a surface)