Newton’s Laws Outline Before we start……. Lets review!!!!!! If someone dropped a bowling ball and a racquet ball from a height of 3m, which would easier for you to catch? Why? Which would hurt more walking or running into a door? Why? Force A ____________________or _____________________ that starts, stops, or changes the direction of an object. The unit for measuring force is a _____________________________, named after Sir Isaac Newton the scientist who explained how forces and motion relate to each other (better known as Newton’s Three Laws of Motion, which we will be covering shortly). They are represented by the size and length of ________________________ Large Force Medium Force Small Force Forces transfer _______________ to an object. Let’s list some forces on the lines below. _________________________ ___________________________ _________________________ ___________________________ _________________________ ___________________________ _________________________ ___________________________ _________________________ ___________________________ _________________________ ___________________________ Forces can act in all ______________________ as well as acting ______________________ each other. Forces act on any object with mass at _______ times. Drawing Forces (aka Free-Body Diagrams) Arrows are used to represent force Ffriction strength and direction. The bigger the (Air Resistance) arrow, the stronger the force. Fnormal Fapplied Ffriction Fgravity Fgravity Now draw force diagrams for the following items in the space below 1. Airplane Types of forces for diagramming. 2. Boat Normal Lift Air Resistance (drag) 3. Car Applied Buoyancy 4. Bicycle Friction Gravity Friction Balanced & Unbalanced Forces __________________ __________ are equal in size but opposite in direction, resulting in no motion. __________________ __________ are unequal in size, resulting in motion. Place your hands together and push. Is this a balanced force? How do you know? Place your hands facing away from your chest and push. Is this a balanced force? How do you know? _______ ___________ is the amount of force left over after 2 forces combine or collide with each other. Forces in the same direction add. + = EXAMPLE: Pushing a car Forces in opposite directions subtract. EXAMPLE: Tug of War + = Calculate the net force in the problems below: 1. net force = _______ 2. net force = _______ 3. net force = _______ 4. net force = _______ Any object, no matter how ________________ will have ___________________bumps that are not noticeable to us because they are so small. __________________ is a force that opposes motion. It comes from objects rubbing against one another. Type of Friction Definition Examples If a feather and a coin were dropped from the same height at exactly the same time, which would hit the ground first? Why? What about in the absence of air resistance? Why? What about skydivers … how do they control the speed of their descent? Lets think!!!!!!!!!!!! If you raced a small mass against a large mass on a flat surface, what mass do you think would win? Why? What about down a ramp? Newton’s First Law of Motion ________________________________________________________ ________________________________________________________ ________________________________________________________ THINK/PAIR/SHARE - - What are some of the outside forces that can change motion, either allowing objects to stay at rest or stop them from moving? ___________________________________________ What can we do about these outside forces that affect our motion? For example, how can we get rid of friction? Materials that reduce friction are called _____________________. Friction can _______________ be eliminated. Examples: 1. _______________________ 2. _______________________ 3. _______________________ 4. _______________________ MORE EXAMPLES OF NEWTON’S 1ST LAW: What happens to an uncovered drink when a car abruptly starts/stops/turns? What happens to an unbelted car occupant during a front – end collision? Why can some people pull a tablecloth out from under dishes without knocking anything over? ________________________is the tendency of an object to resist any change in motion. It is completely dependent upon _______________________ The more __________________ the more ___________________. EXAMPLES: A bicycle rider is no longer pedaling, but the bike keeps moving forward, why? What forces act on the bike to slow it down? Which would have more inertia … Bowling ball or golf ball? Car or airplane? Gallon of milk or a 12 ounce soda? Newton’s Second Law of Motion _____________________________________________________________ _____________________________________________________________ Newton understood that _________________, __________________, and ________________________ are related. He showed that the motion of an object changes when an outside force is applied (1 st law). He also showed that knowing the mass and the acceleration of an object, you could calculate its force (2nd law). Today this observation has been restated as the SECOND LAW OF MOTION, the net force on an object equals its mass times its acceleration _____________________= ______________X __________________ If the force remained constant and mass increased, acceleration would __________________. and mass decreased, acceleration would __________________. If the mass remained constant … and acceleration increased, the force would ____________________. and acceleration decreased, the force would ____________________. EXAMPLE: Walking versus running into a wall ! Example Word Problems 1. How much force is needed to accelerate a 20 kg crate by 3m/s/s? 1. mass = _______________________ 2. acceleration = __________________ 3. force = _______________________ How much force must be added to the 2. push it with 120 N of force? 1. mass = _______________________ 2. acceleration = __________________ 3. force = _______________________ What is the force applied to each cart? a = 2.5 m/s2 a = 1.5 m/s2 Use your formula!!!!!! 30.0 kg 30.0 kg How much force would you need 20.0 kg To add to the cart on the right if they are to have the Acceleration (m/s2) same acceleration? 100 kg 200 kg This is a graph of force versus acceleration for a dog sled race. As the force increases so does the Force (N) acceleration. What can you conclude about how mass effects acceleration from the graph? How would the addition of another dog effect the acceleration of the sled? Newton’s Second Law of Motion can also be used to calculate an object’s weight. WHY? Because we know that your weight is calculated by the acceleration of gravity (9.8 m/s/s) X whatever your mass is. Each planet has a different acceleration of gravity because gravity is dependent upon the size of the planet. So how would your weight differ from planet to planet? ___________________________________________________ ___________________________________________________ All objects accelerate at 9.8 m/s/s. However all falling objects are affected by __________________________, which can cause different objects to actually fall faster. When one object stops accelerating because of air resistance, the object has reached its ______________________ _______________________. What types of objects would probably reach terminal velocity very quickly as the fall? ___________________________________________________ Falling objects also experience __________________________. While an object is in freefall, the weight of the object is zero. This is because there is nothing to ____________ _______________ on the falling object. This leads us into the third law of motion. Newton’s Third Law of Motion When one object exerts a force upon a second object, the second object exerts and equal and opposite force upon the first object … OR … ________________________________________________________ ________________________________________________________ When you sit on a chair, your body exerts a force on that ______________, the chair in turn exerts a force on your_______________. This is why you do not fall through the chair. When you place a book on a table, the book exerts a force on that____________________, the table in turn exerts a force on the _______________________. In the example of the balloon, the force propelling the balloon is equal and opposite to the force of the air leaving the balloon. Apply Newton’s Three Laws of Motion DIRECTIONS: Use your group, your textbooks, your notes, and your prior knowledge of Newton’s Three Laws of Motion to answer the following questions IN COMPLETE SENTENCES. Part A: Newton’s First Law of Motion and Friction 1. Recall or find Newton’s First Law of Motion and write it here. 2. Newton’s first law is sometimes called the “Law of Inertia”. Write the definition of inertia below. What is inertia solely dependent upon? 3. If Newton’s first law is true, then, consider the following questions and try to answer them: a. Why won’t a book slide forever if I give it a push across the floor? b. Why do I need a gas pedal in my car? Can’t I just give my car a little push and it will roll forever? c. What force is acting on the book and car to slow them down? 4. Imagine a place in space, far from all gravitational and frictional forces. Suppose that an astronaut throws a rock. The rock will: (Circle your answer.) a. gradually stop. b. continue in motion in the same direction at constant speed. 5. In space, in a weightless environment, would it require a force to set an object in motion? Explain your answer. 6. Ben Too Close is being chased through the woods by a bull moose which he was attempting to photograph. The enormous mass of the bull moose is extremely intimidating. Yet, if Ben makes a zigzag pattern through the woods, he will be able to use the large mass of the moose to his own advantage. Explain this in terms of inertia and Newton's first law of motion. 7. A marble dropped into a bottle of liquid soap quickly reaches a terminal velocity. What is the acceleration of the marble just before it hits the bottom of the container? Part B: Newton’s 2nd Law of Motion 1. State Newton’s 2nd Law of Motion and write the formula that explains Newton’s 2nd Law. Define each variable in the formula. 2. What two factors affect the rate of acceleration of an object according to Newton’s 2nd Law? 3. According to Newton’s 2nd Law, what happens to the acceleration of a rocket if the net force is doubled? 4. Find Acceleration. a. What is the acceleration of a 500kg corvette if the net force on the corvette is 2,000N? b. What is the acceleration of a 1,000kg car if the net force on the car is 3,000N? c. The net horizontal force on a 50,000kg railroad boxcar is 4,000N. What is the acceleration of the boxcar? d. A fully equipped astronaut has a mass of 150kg. If the astronaut has a weight of 555N standing on the surface of Mars, what is the acceleration due to gravity on Mars? 5. Find the Net Force. a. What is the net force needed to accelerate a 50.0 kg bowling ball at 2.0m/s2? b. A skydiver with a mass of 80.0 kg is accelerating at 4.0 m/s2. What is the force of the air resistance acting on the skydiver? c. An unbalanced force gives a 2.00kg mass an acceleration of 5.00m/s2. What is the force applied to the object? d. A racing car has a mass of 710kg. It starts from rest and travels 120m in 3.0s. The car undergoes uniform acceleration during the entire 3.0s. What is the unbalanced force applied to the car? 6. Find the Mass. a. If a skydiver has a net force of 400N and an acceleration of 5m/s2, what is the mass of the skydiver? b. A child on roller blades accelerates at 5.0 m/s2, due to a horizontal net force of 18.0N. What is the mass of the child? c. An unbalanced force of 20N gives a stone an acceleration of 4.0m/s2. What is the mass of the stone? d. An unbalanced force of 25N is used to accelerate an object at a rate of 2.1m/s2. What is the mass of the object? Part C: Newton’s 3rd Law and Momentum 1. State Newton’s 3rd Law. 2. Explain how Newton’s 3rd Law is at work when you walk. 3. Or when you are just standing on the ground.
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