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S-24 I can explain the relationship between weight, gravity, and friction Define the following terms A. Weight B. Gravity C. Friction S-25 I can describe different kinds of force. What does friction normally do to a moving object? What would be different in the world if there was not friction? Chapter 12 Newton’s Laws SPS8 Students will determine relationships among force, mass, and motion. b. Apply Newton’s three Laws to everyday situations. c. Relate falling objects to gravitational force. d. Explain the difference in mass and weight. 12.1 Forces How do forces affect the motion of an object? What the four main types of friction? How do gravity and air resistance affect a falling object? In what direction does Earth’s gravity act? 12.1 Force 12.1 Forces How do forces affect the motion of an object? Force – a push or a pull on an object Forces cause changes in velocity Acceleration - change the objects speed or direction Measured Scale, Force Sensor Unit – measured in Newton’s (N) A medium apple will apply a force of about 1 N 12.1 Force 12.1 Forces How do forces affect the motion of an object? Forces are vectors so they are drawn using arrows (show magnitude and direction) Net Force – the overall force acting on an object after all the forces are combined Balanced forces – the net force is zero, no acceleration Unbalanced forces – objects accelerate 12.1 Force 12.1 Forces What are the four main types of friction Friction – a force that opposes the motion of objects that touch as they move past each other Four Types Static Friction – when objects aren’t moving Sliding Friction – when objects are sliding past each other 12.1 Force 12.1 Forces What are the four main types of friction Rolling Friction – allows movement forward, but not side to side Fluid Friction – when an object is moving through a fluid ▪ Fluids are liquids or gases – anything that flows ▪ Air resistance is a form of fluid friction 12.1 Force 12.1 Forces How does gravity and air resistance affect a falling object Gravity – the force of attraction between any two objects with mass Earth’s gravity points toward the center of the earth – pulls anything with mass Called weight 12.1 Force 12.1 Forces How does gravity and air resistance affect a falling object When an object is falling, two forces act on it What do you think they are? ▪ Weight ▪ Air Resistance Air Resistance Objects will accelerate because of gravity until they reach a terminal velocity – the speed at which the weight and air resistance are equal For example – terminal Gravity speed of a raindrop is about (Weight) 9 m/s Human – 76 m/s S-26 I can describe different kinds of force. Name and describe the four types of friction. S-27 I can describe different kinds of force. What is the difference between weight and mass. 12.2 Newton’s 1st and 2nd Laws of Motion How does Newton’s first law relate change in motion to a zero net force? How does Newton’s second law relate force, mass, and acceleration? How are weight and mass related? 12.1 Force 12.2 Newton’s 1st & 2nd Laws How does Newton’s first law relate change in motion to a zero net force Newton’s First Law of Motion The state of motion of an object does not change as long as the net force acting on the object is zero More commonly ▪ An object at rest remains at rest, and an object in motion remains in motion, unless acted on by an outside force. Sometimes called the law of inertia ▪ Inertia – the tendency of an object to resist a change in its motion 12.1 Force 12.2 Newton’s 1st & 2nd Laws How does Newton’s second law relate force, mass, and acceleration Newton’s Second Law of Motion The acceleration of an object is equal to the net force acting on it divided by the object’s mass. F ma F – Force in Newtons m – mass in kilograms a – acceleration in m/s2 Always in the same direction as the net force 12.1 Force 12.2 Newton’s 1st & 2nd Laws How does Newton’s second law relate force, mass, and acceleration b c Newton’s Second Law of Motion – Practice m F ma Problems a 4000 N 1000 kg a 4 2 A car with a mass of 1000 kg accelerates when s the traffic light turns green. If the net force on the car is 4000 N, what is the cars acceleration? Equation? Variables? Filled In Equation? Answer? m 1000 kg F 4000 N 12.1 Force 12.2 Newton’s 1st & 2nd Laws How does Newton’s second law relate force, mass, and acceleration d c e b Newton’s Second Law of Motion – Practice m ffffff F ma Problems FAnautomobile 1200 3.0 F with kg 400 N a mass of 1200 kg s 2 accelerates at a rate of 3.0 m/s2. What is the force acting on the automobile? Equation? Variables? Filled In Equation? Answer? m 1200 kg a 3.0 ms 2 12.1 Force 12.2 Newton’s 1st & 2nd Laws How does Newton’s second law relate force, mass, and acceleration d e Newton’s Second Law of Motion – Practice m ffffff F ma Problems 25 N m 0.5 m 50 kg A 25 N force accelerates a man on a scooter 2 at s and 0.5 m/s2. What is the mass of the man scooter? Equation? Variables? Filled In Equation? Answer? F 25 N a 0.5 ms 2 12.1 Force 12.2 Newton’s 1st & 2nd Laws How are weight and mass related Weight and Mass Weight the force of gravity acting on an object Its mass times acceleration due to gravity W mg W – Weight in Newtons m – mass in kilograms g – 9.80 m/s2 12.1 Force 12.2 Newton’s 1st & 2nd Laws How are weight and mass related Weight and Mass Mass is a measurement of the inertia of an object Weight is a measurement of the force of gravity acting on an object 12.3 Newton’s 3rd Law of Motion and Momentum What is Newton’s third law of motion? 12.1 Force 12.3 Newton’s 3rd Law What is Newton’s third law of motion Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. Identify the following action and reaction forces 12.1 Force 12.3 Newton’s 3rd Law What is Newton’s third law of motion Newton’s Third Law Action-Reaction pairs can cause motion The donkey pushes on the ground, the ground pushes the donkey forward Does the donkey push the ground backward? Action-Reaction pairs don’t cancel They don’t act on the same objects 12.4 Universal Forces What are the four fundamental forces? 12.1 Force 12.4 Universal Forces What are the four fundamental forces Electromagnetic Forces Associated with charged particles Electric Force – between two charged particles Negative and positive Opposites attract, like repels Magnetic Force – between other magnets and certain metals 12.1 Force 12.4 Universal Forces What are the four fundamental forces Strong Nuclear Force Act to hold the nucleus together Overcomes repulsion of positive protons with each other The strongest force over small (tiny, tiny) distances 12.1 Force 12.4 Universal Forces What are the four fundamental forces Weak Nuclear Force Involved in certain types of radioactive processes Active only over distances even smaller than the strong nuclear force 12.1 Force 12.4 Universal Forces What are the four fundamental forces Gravitational Force Between any two objects with mass Depends on the mass and the distance between the objects Very weak force Acts over very long distances