Overview The Laws of Motion

Directed Reading for Content Mastery Overview The Laws of Motion Directions: Fill in the blanks using the terms listed below. force inertia momentum sliding conservation of momentum gravitational ma mv opposite weight centripetal downward I. Newton s First Law A. defined as: an object in motion stays in motion unless acted upon by a net B. is the tendency of an object to resist a change in motion. II. Newton s Second Law A. defined as: net force acting on an object causes the object to accelerate in the direction of the net force; F = B. types of forces 1. occurs between any two objects. a. is the gravitational force exerted on an object by Earth. b. An object that is shot or thrown follows a path because of the force of gravity pulling it. 2. causes an object to move in a circle. II. Newton s Third Law A. defined as: to every action force there is an equal and reaction force B. : a property a moving object has because of its mass and velocity; p = C. : momentum transfers from one object to another with the total momentum being conserved The Laws of Motion 19

Directed Reading for Content Mastery Section 1 The First Two Laws of Motion Section 2 Gravity Directions: In the blank at the left, write the letter of the term that correctly completes each statement. 1. Every object in the universe exerts a force on every other object. This force is called. a. friction b. gravity 2. The measure of the gravitational force exerted by Earth on an object is the object s. a. weight b. mass 3. The amount of gravitational force between two objects depends on their. a. color and density b. mass and distance 4. Weight is measured in units called. a. newtons b. kilograms 5. The greater an object s, the stronger the gravitational force on it. a. mass b. velocity 6. Mass is measured in units called. a. newtons and kilonewtons b. grams and kilograms 7. A weight reading on a scale shows the exerted by the scale. a. upward force b. downward force 8. Earth exerts a stronger gravitational force than the moon because Earth has more. a. mass b. density 9. The masses of your hand and your notebook are quite small, so the force of attraction between them is. a. zero b. weak 10. An object transported from the surface of Earth to the surface of the Moon has its weight. a. decreased b. stay the same 20 The Laws of Motion

Directed Reading for Content Mastery Section 3 The Third Law of Motion Directions: Choose the term from the list below that is best described by each statement. Write the term to the left of each statement. momentum reaction Newton s third law of motion conservation of momentum velocity mass action 1. When one object exerts a force on a second object, the second object exerts a force that is equal in size and opposite in direction. 2. The backward kick of a rifle that is fired is an example of a(n) force. 3. The total amount of momentum of a group of objects does not change unless outside forces act on the objects. 4. Air rushing out of the neck of a balloon causes the balloon to move. The air that comes from the balloon is an example of a(n) force. 5. In the equation p = m v, p represents. 6. Momentum has direction because has direction. 7. Momentum is a property a moving object has because of its and velocity. Directions: Think for a minute about Newton s third law of motion. Can you remember any event when you experienced this law? If so, draw a diagram below to show the action-reaction forces. If you can t remember an event that you experienced, think up one and draw it below. 8. The Laws of Motion 21

Directed Reading for Content Mastery Key Terms The Laws of Motion Directions: Determine whether the italicized term makes each statement true or false. If the statement is true, write the word true in the blank. If the statement is false, write in the blank the term that makes the statement true. 1. Objects fall toward Earth at a rate of 9.8 m/s 2 because of centripetal force. 2. F = ma represents Newton s second law of motion. 3. Acceleration toward the center of a curved or circular path is called gravitational acceleration. 4. In p = mv, p represents position. 5. The force of gravity acting upon an object is the object s mass. 6. Inertia is the tendency of an object to resist a change in its motion 7. To every action force there is an equal and opposite reaction force is the law of conservation of momentum. 8. According to the law of conservation of momentum, momentum lost equals momentum gained. 9. The force keeping a ball on a string moving in a circle is inertia. 10. Anything that is thrown or shot through the air is weightless. 11. According to the third law of motion, an object at rest will stay at rest unless acted upon by a net force. 22 The Laws of Motion

Name Date Class Chapter Review The Laws of Motion Part A. Vocabulary Review Directions: In the space at the left, write the term from the list that correctly completes each statement. gravity weight distance newtons momentum inertia Newton s second law of motion projectile centripetal force Newton s third law of motion centripetal acceleration Newton s first law of motion conservation of momentum 1. The phrase to every action there is an equal and opposite reaction is. 2. The tendency of an object not to change its motion is its. 3. A ball thrown across a football field is an example of a(n). 4. When an object moves in a circle, acts to accelerate the object toward the center of that circle. 5. When a car travels around a curve in the road, helps to keep the car traveling in a curved path. 6. An object at rest stays at rest because of. 7. A net force acting on an object causes the object to accelerate in the direction of the force; this is. 8. A property of a moving object resulting from its mass and velocity is. 9. According to the, when a bowling ball strikes the pins, the momentum lost by the bowling ball is equal to the momentum gained by the pins. 10. is the force that every object in the universe exerts on every other object. 11. An object s is the measure of the force of gravity on that object. 12. The amount of gravitational force between two objects depends on their masses and the between them. 13. Weight is measured in units called, while mass is measured in units called grams and kilograms. Assessment The Laws of Motion 37

Chapter Review (continued) Part B. Concept Review 1. In the diagram at the right, a satellite is shown orbiting Earth. Add three arrows to the diagram to indicate the effects of a. inertia, b. gravity, and c. the path you predict results from the effects of inertia and gravity. Label the arrows a, b, and c. Satellite 2. Complete the diagrams below by indicating the path of the ball in each situation. Orbit path a. The ball is placed on the edge of a table and allowed to fall to the floor. b. The ball is rolled rapidly across the table and falls onto the floor. 3. The balls in the figure above have the same mass. If the balls are dropped from the table at the same time, which ball will hit the floor first? Assessment 4. If a 2-kg ball is thrown through the air at 20 m/s, what is the momentum of the ball? 5. Why would a flat sheet of paper and a wad of paper with the same mass not fall through the air at the same rate? 6. When is something weightless? 7. A toy train with a mass of 2 kg moving at 10 m/s collides with a 2-kg toy train that is stationary. If the two trains couple, what will be their speed after impact? 38 The Laws of Motion

Name Date Class Chapter Test The Laws of Motion I. Testing Concepts Directions: For each of the following, write the letter of the term or phrase that best completes each statement or answers each question. 1. The downward force exerted on an object falling through air is. a. terminal velocity c. gravity b. momentum d. weightless 2. When an object moves in a circular path, it accelerates toward the center of the circle as a result of. a. terminal velocity c. centripetal force b. momentum d. friction 3. The statement to every reaction there is an equal and opposite reaction is. a. the law of conservation of momentum c. Newton s second law of motion b. Newton s first law of motion d. Newton s third law of motion 4. In the equation, p = mv, p represents. a. momentum b. friction c. inertia d. velocity 5. Momentum is expressed in units of. a. kg m b. kg m/s c. N d. m/s 2 6. An object that is in free fall seems to be. a. weightless c. speeded up by air resistance b. slowed by air resistance d. not moving 7. The relationship among mass, force, and acceleration is explained by. a. Newton s first law of motion c. Newton s third law of motion b. Newton s second law of motion d. the conservation of momentum 8. When two objects collide, their momentum after the collision is explained by. a. Newton s first law of motion c. Newton s third law of motion b. Newton s second law of motion d. the conservation of momentum 9. A feather will fall through the air more slowly than a brick because of. a. gravity b. air resistance c. inertia d. momentum 10. In the absence of air, a penny and a feather dropped from the same height will. a. fall at different rates c. fall at the same rates b. float d. not have momentum 11. The amount of gravitational force between objects depends on their. a. frictional forces c. inertia b. speed and direction d. masses and the distances between them 12. The path of a projectile is. a. straight b. always vertical c. always horizontal d. curved Assessment The Laws of Motion 39

Chapter Test (continued) 13. The motion of an object parallel to Earth s surface is. a. horizontal b. vertical c. weightlessness d. momentum 14. If a 300-N action force is exerted to the right, the reaction force will be. a. 300 N to the right c. 300 N to the left b. 600 N to the right d. 600 N to the left 15. When a force is exerted on an object, an equal and opposite force is exerted by the object. These forces are referred to as. a. centripetal forces c. gravitational forces b. friction forces d. action-reaction forces 16. Acceleration due to gravity is. a. 98 m/s 2 b. 9.8 m/s 2 c. 9.8 m/s d. 0.98 m/s 17. A real car moving at 10 km/h has more momentum than a toy car moving at the same rate because. a. its mass is greater c. it moves faster b. its mass is less d. of friction 18. An object attached to a string that is being swung in a clockwise circular path is shown. Assume the string breaks at point A. In which direction will the object be traveling an instant later? Point A Assessment a. b. c. d. 19. According to Newton s second law of motion,. a. F = mv b. F = ma c. F = pv d. F = pa 20. The inertia of an object depends on its. a. momentum b. speed c. mass d. weight 21. Gravity is one of basic forces. a. two b. three c. four d. five 22. A car rounding a curve is subject to force. a. rolling b. static c. centripetal d. gravitational 40 The Laws of Motion

Chapter Test (continued) II. Understanding Concepts Skill: Designing an Experiment 1. How could you use two equal-sized pieces of paper to show how air resistance affects objects of different shapes? Skill: Making and Using Tables 2. Complete the table below by calculating the missing values. Object Mass Velocity Momentum A B C D 10 kg 25 m/s 25 m/s 300 kg m/s 25 kg 300 kg m/s 25 m/s 500 kg m/s 3. Use the information in the table above to answer the following questions. a. Which object has the greatest momentum? b. Which object has the least momentum? c. How does the momentum of object B compare with the momentum of object C? d. Why is the momentum for object B greater than the momentum for object A? e. What factor causes object D to have a greater momentum than object C? Skill: Concept Mapping 4. In an events chain concept map showing what happens when a bowling ball strikes the pins, how does the momentum of the bowling ball change at the time of impact? 5. What happens to the momentum of the pins at impact? Assessment The Laws of Motion 41

Chapter Test (continued) III. Applying Concepts Directions: Do the following calculations. Show your work in the spaces provided. 1. What is the force of an object with a mass of 12 kg and an acceleration of 4 m/s 2? 2. Calculate the acceleration of a 25-kg object that is moved with a force of 300 N. 3. What is the mass of an object that is accelerating at 15 m/s 2 when a force of 3000 N is exerted? IV. Writing Skills Directions: Answer the following questions using complete sentences. 1. Two objects that have the same mass are dropped from the top of a 20-m high building. One object is larger and flatter than the other object. Explain why the larger, flatter object hits the ground last. Assessment 2. What are two examples of gravitational force in your daily life? 3. How is mass different from weight? 42 The Laws of Motion

1 Reinforcement The First Two Laws of Motion Directions: Use the equation F = m a to solve the following problems. Show your calculations in the spaces provided. 1. How much force is needed to accelerate a 1000-kg car at a rate of 3 m/s 2? 2. If a 70-kg swimmer pushes off a pool wall with a force of 250 N, at what rate will the swimmer accelerate from the wall? 3. A weightlifter raises a 200-kg barbell with an acceleration of 3 m/s 2. How much force does the weightlifter use to raise the barbell? 4. A dancer lifts his partner above his head with an acceleration of 2.5 m/s 2. The dancer exerts a force of 200 N. What is the mass of the partner? Directions: Answer the following questions on the lines provided. 5. What does Newton s second law of motion state? 6. What two factors affect the rate of acceleration of an object? 7. What is inertia? 8. Explain how Newton s first law can be derived from Newton s second law. The Laws of Motion 27

2 Reinforcement Gravity Directions: Answer the following questions on the lines provided. 1. What is gravity? 2. What are two things that the amount of gravitational force between two objects depends on? 3. Why does Earth exert a stronger gravitational force than the Moon? 4. If an object weighs 40 N on Earth, would it weigh more than 40 N on the Moon? Explain. Directions: Use the diagrams below to complete the following questions. A Dry road Icy road 5. What is the centripetal force that allows a car to move around a sharp curve in a roadway? 6. Draw an arrow on the bottom diagram to show the movement of the car if the centripetal force of the road and car is not enough to overcome the car s inertia when it reaches point B. 7. Explain how you know the car is accelerating when it reaches point A in the first diagram. B 28 The Laws of Motion

3 Reinforcement The Third Law of Motion Directions: Use the illustrations to answer the following questions. Figure A Figure B 1. Draw an arrow on Figure A to show the direction the cannon will move when the cannonball is fired. 2. Draw arrows on Figure B to show the direction the oars must move to propel the boat forward. 3. Does the arrow you drew on Figure A represent an action force or a reaction force? 4. Do the arrows you drew on Figure B represent an action force or a reaction force? 5. If the force that propels the cannonball forward is 500 N, how much force will move the cannon backward? Explain. Directions: Solve the following problems. 6. What is the momentum of a 2-kg toy truck that moves at 10 m/s? 7. What is the momentum of a 2000-kg truck that moves at 10 m/s? 8. Which truck has more momentum? Why? The Laws of Motion 29

1 Enrichment Friction and the Curve Ball The curve ball was invented by a young pitcher named Arthur Candy Cummings. Although Cummings first threw the curve ball during a game while pitching for the Brooklyn Excelsiors in 1867, he actually invented his technique many years before. As a boy, Cummings loved baseball and practiced his pitching on the beach near his New England home. He threw clam shells instead of a baseball and found that by holding and releasing the shells in a certain way he could make them curve. Did it really curve? The Baseball Hall of Fame gave Cummings the title inventor of the curve ball. In his historical performance, Cummings snapped his wrist at the exact moment when he released the ball. This caused it to arch and fly past the batter to land in the catcher s mitt. People couldn t believe it. Nobody knew for sure whether the ball really curved or just looked like it did. More than 100 years later in 1982, the Massachusetts Institute of Technology (MIT) proved once and for all that a baseball thrown like Cummings threw it does, indeed, curve. Why does it curve? It s all about friction. The snap action of the pitcher s wrist puts a spin on the ball. And that spin changes the friction between the air and the ball. After it s thrown, parts of the ball experience more air friction and parts of the ball experience less. A curved path results from the ball moving toward the least amount of friction. Specifically, one movement of the pitcher s wrist when the ball is released causes a top spin, making the top of the ball move forward against the air (more friction) and the bottom move in the same direction as the air (less friction). Like any curve ball, the ball curves toward the least amount of friction: downward. Spin It Sideways In addition to topspin, a pitcher s wrist can also produce a counter-clockwise spin or a clockwise spin. When a curveball is thrown by a right-handed pitcher, the ball spins counterclockwise. The right side of the baseball experiences less air friction, and the ball curves to the left, or away from a right-handed hitter. When a curveball is thrown by a left-handed pitcher, the ball spins clockwise. The left side of the baseball experiences less air friction, and the ball curves to the right, or away from left-handed batters. 1. What effect might the stitches on a baseball have on the path of a baseball? 2. Do you think a baseball curves better at the top of a high mountain or down on a flat plain? Explain. 3. Describe how the type of spin given to a baseball by a pitcher influences the path of the baseball. 30 The Laws of Motion