Physics
Newton's Laws
Newton's Laws of Motion are fundamental principles in physics. The first law states that an object at rest will remain at rest, and an object in motion will remain in motion unless acted upon by an external force. The second law describes how the force acting on an object is related to its mass and acceleration. The third law states that for every action, there is an equal and opposite reaction.
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11 Key excerpts on "Newton's Laws"
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler, Heath Jones, Matthew Collins, John Daicopoulos, Boris Blankleider(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Collectively they are called ‘Newton’s laws of motion’ and provide the basis for understanding the effect that forces have on an object. Because of the importance of these laws, a separate section will be devoted to each one. 4.2 Newton’s first law of motion LEARNING OBJECTIVE 4.2 Define Newton’s first law of motion. The first law To gain some insight into Newton’s first law, think about the game of ice hockey (figure 4.2). If a player does not hit a stationary puck, it will remain at rest on the ice. After the puck is struck, however, it coasts on its own across the ice, slowing down only slightly because of friction. Since ice is very slippery, there CHAPTER 4 Forces and Newton’s laws of motion 79 is only a relatively small amount of friction to slow down the puck. In fact, if it were possible to remove all friction and wind resistance, and if the rink were infinitely large, the puck would coast forever in a straight line at a constant speed. Left on its own, the puck would lose none of the velocity imparted to it at the time it was struck. This is the essence of Newton’s first law of motion. Newton’s first law of motion An object continues in a state of rest or in a state of motion at a constant velocity (constant speed in a constant direction), unless compelled to change that state by a net force. FIGURE 4.2 The game of ice hockey can give some insight into Newton’s laws of motion. In the first law the phrase ‘net force’ is crucial. Often, several forces act simultaneously on a body, and the net force is the vector sum of all of them. Individual forces matter only to the extent that they contribute to the total. For instance, if friction and other opposing forces were absent, a car could travel forever at 30 m/s in a straight line, without using any gas after it had come up to speed. In reality gas is needed, but only so that the engine can produce the necessary force to cancel opposing forces such as friction.
eBook - PDF- Paul Peter Urone, Roger Hinrichs(Authors)
- 2012(Publication Date)
- Openstax(Publisher)
Newton’s second law of motion is more than a definition; it is a relationship among acceleration, force, and mass. It can help us make predictions. Each of those physical quantities can be defined independently, so the second law tells us something basic and universal about nature. The next section introduces the third and final law of motion. 4.4 Newton’s Third Law of Motion: Symmetry in Forces There is a passage in the musical Man of la Mancha that relates to Newton’s third law of motion. Sancho, in describing a fight with his wife to Don Quixote, says, “Of course I hit her back, Your Grace, but she’s a lot harder than me and you know what they say, ‘Whether the stone hits the pitcher or the pitcher hits the stone, it’s going to be bad for the pitcher.’” This is exactly what happens whenever one body exerts a force on another—the first also experiences a force (equal in magnitude and opposite in direction). Numerous common experiences, such as stubbing a toe or throwing a ball, confirm this. It is precisely stated in Newton’s third law of motion. Newton’s Third Law of Motion Whenever one body exerts a force on a second body, the first body experiences a force that is equal in magnitude and opposite in direction to the force that it exerts. This law represents a certain symmetry in nature: Forces always occur in pairs, and one body cannot exert a force on another without experiencing a force itself. We sometimes refer to this law loosely as “action-reaction,” where the force exerted is the action and the force experienced as a consequence is the reaction. Newton’s third law has practical uses in analyzing the origin of forces and understanding which forces are external to a system. We can readily see Newton’s third law at work by taking a look at how people move about. Consider a swimmer pushing off from the side of a pool, as illustrated in Figure 4.9. She pushes against the pool wall with her feet and accelerates in the direction opposite to that of her push.
eBook - PDF- Daniel Kleppner, Robert Kolenkow(Authors)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
NEWTON’S LAWS 2 2.1 Introduction 48 2.2 Newtonian Mechanics and Modern Physics 48 2.3 Newton’s Laws 49 2.4 Newton’s First Law and Inertial Systems 51 2.5 Newton’s Second Law 51 2.5.1 Mass 52 2.5.2 Force 53 2.6 Newton’s Third Law 54 2.6.1 Fictitious Forces 57 2.7 Base Units and Physical Standards 59 2.7.1 Time 60 2.7.2 Length 61 2.7.3 Mass 61 2.7.4 Systems of Units 62 2.8 The Algebra of Dimensions 63 2.9 Applying Newton’s Laws 64 2.10 Dynamics Using Polar Coordinates 72 Problems 77 48 NEWTON’S LAWS 2.1 Introduction Our goal in this chapter is to understand Newton’s laws of motion. New-ton’s laws are simple to state and they are not mathematically complex, so at first glance the task looks modest. As we shall see, Newton’s laws combine definitions, observations from nature, partly intuitive concepts, and some unexamined assumptions about space and time. Newton’s pre-sentation of his laws of motion in his monumental Principia (1687) left some of these points unclear. However, his methods were so successful that it was not until two hundred years later that the foundations of New-tonian mechanics were carefully examined, principally by the Viennese physicist Ernst Mach. Our treatment is very much in the spirit of Mach. Newton’s laws of motion are by no means self-evident. According to Aristotle, the natural state of bodies is rest: bodies move only when a force is applied. Aristotelian mechanics was accepted for two thousand years because it seemed intuitively correct. Careful reasoning from ob-servation and a great leap of imagination were needed to break out of the Aristotelian mold. Analyzing physical systems from the Newtonian point of view re-quires e ff ort, but the payo ff is handsome. To launch the e ff ort, this chap-ter is devoted to presenting Newton’s laws and showing how to apply them to elementary problems.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Collectively they are called “Newton’s laws of motion” and provide the basis for understanding the effect that forces have on an object. Because of the importance of these laws, a separate section will be devoted to each one. 4.2 | Newton’s First Law of Motion The First Law To gain some insight into Newton’s first law, think about the game of ice hockey (Figure 4.2). If a player does not hit a stationary puck, it will remain at rest on the ice. After the puck is struck, however, it coasts on its own across the ice, slowing down only slightly because of friction. Since ice is very slippery, there is only a relatively small amount of friction to slow down the puck. In fact, if it were possible to remove all friction and wind resistance, and In order to successfully land the planetary rover, Curiosity, on the surface of Mars, NASA scientists and engineers had to take into account many forces, such as the thrust from the “sky crane” rocket en- gines, the tension in its towing cables, air resistance, and the weight of the rover due to the gravity on Mars, just to name a few. This chapter will discuss how forces influence the motion of objects. 4 | Forces and Newton’s Laws of Motion Chapter | 4 © Stocktrek Images 79 LEARNING OBJECTIVES After reading this module, you should be able to... 4.1 | Discuss the concepts of force and mass. 4.2 | Define Newton’s first law of motion. 4.3 | Define Newton’s second law of motion. 4.4 | Apply Newton’s second law of motion in two dimensions. 4.5 | Apply Newton’s third law of motion. 4.6 | Identify types of forces. 4.7 | Define Newton’s law of universal gravitation. 4.8 | Solve problems using the normal force. 4.9 | Solve problems involving friction. 4.10 | Solve problems involving tension. 4.11 | Apply Newton’s first law to equilibrium problems. 4.12 | Apply Newton’s second law to nonequilibrium problems.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
Collectively they are called “Newton’s laws of motion” and provide the basis for understanding the effect that forces have on an object. Because of the importance of these laws, a separate section will be devoted to each one. 4.2 | Newton’s First Law of Motion The First Law To gain some insight into Newton’s first law, think about the game of ice hockey (Figure 4.2). If a player does not hit a stationary puck, it will remain at rest on the ice. After the puck is struck, however, it coasts on its own across the ice, slowing down only slightly because of friction. Since ice is very slippery, there is only a relatively small amount of friction to slow down the puck. In fact, if it were possible to remove all friction and wind resistance, and 4 | Forces and Newton’s Laws of Motion © Stocktrek Images In order to successfully land the planetary rover, Curiosity, on the surface of Mars, NASA scientists and engineers had to take into account many forces, such as the thrust from the “sky crane” rocket en- gines, the tension in its towing cables, air resistance, and the weight of the rover due to the gravity on Mars, just to name a few. This chapter will discuss how forces influence the motion of objects. Chapter | 4 LEARNING OBJECTIVES After reading this module, you should be able to... 4.1 | Discuss the concepts of force and mass. 4.2 | Define Newton’s first law of motion. 4.3 | Define Newton’s second law of motion. 4.4 | Apply Newton’s second law of motion in two dimensions. 4.5 | Apply Newton’s third law of motion. 4.6 | Identify types of forces. 4.7 | Define Newton’s law of universal gravitation. 4.8 | Solve problems using the normal force. 4.9 | Solve problems involving friction. 4.10 | Solve problems involving tension. 4.11 | Apply Newton’s first law to equilibrium problems. 4.12 | Apply Newton’s second law to nonequilibrium problems. 70 if the rink were infinitely large, the puck would coast forever in a straight line at a constant speed.
eBook - PDFSystemic Yoyos
Some Impacts of the Second Dimension
- Yi Lin(Author)
- 2008(Publication Date)
- Auerbach Publications(Publisher)
More specifically, after introducing the new figurative analysis method, we will have a chance to generalize all three laws of motion so that external forces are no longer required for these laws to work. As what is known, these laws are one of the reasons why physics is an exact science. It can be expected that these generalized forms of the laws will be equally applicable to social sciences and humanity areas as their classic forms in natural science. To this end, please consult the remaining chapters in this book. The presentations in this chapter and the following two chapters are based on Lin (2007). 4.1 The Second Stir and Newton’s First Law of Motion Newton’s first law says that an object will continue in its state of motion unless compelled to change by a force impressed upon it. This property of objects, their natural resistance to changes in their state of motion, is called inertia. Based on the theory of blown-ups, one has to address two questions not settled by Newton in his first law: Question 4.1. If a force truly impresses on the object, the force must be from outside of the object. Then, where can such a force be from? Question 4.2. This problem is about the so-called natural resistance of objects to changes in their state of motion. Specifically, how can such a resistance be considered natural? Newton’s Laws of Motion n 53 It is because uneven densities of materials create twisting forces that fields of spinning currents are naturally formed. This end provides an answer and explana-tion to Question 4.1. Based on the yoyo model (Figure 1.1), the said external force comes from the spin field of the yoyo structure of another object, which is a level higher than the object of our concern. The forces from this new spin field push the object of concern away from its original spin field into a new spin field. If there were not such a forced traveling, the said object would continue its original movement in its original spin field.
eBook - PDFApplied Mathematics
Made Simple
- Patrick Murphy(Author)
- 2014(Publication Date)
- Butterworth-Heinemann(Publisher)
If a boy runs forward with a velocity ν carrying a plastic windmill of mass m, the linear momentum of the windmill is mv regardless of the direction in which the windmill is rotating about its centre. Since linear momentum is the product of a mass (kilogrammes) and a velocity (metres per second), it follows that the unit of momentum is kilo-gramme metre per second (abbreviated to k g m s 1 ) . For example, if each wheel of a car has a mass of 10 kg, the momentum of each wheel when the car is travelling with a velocity of 15 m s 1 is 150 kg m s 1 . If the total mass of the car and occupants is 1000 kg, the momentum of the car and occupants is 15000 k g m s -1 . Newton's Laws of Motion may be stated as follows: 1. Every body will continue in a state of rest or uniform motion in a straight line unless acted upon by an external applied force. 2. The rate of change of motion is proportional to the applied force and takes place in the direction of that force. 3. T o each action there is an equal and opposite reaction. The third law has already been discussed in Chapter One (page 9). It is not possible to give a proof of these laws, but there is a great deal of experimental evidence for assuming their truth. The assumption that the laws are true is borne out by the fact that the motions of the stars and planets have been, and are, computed with a high degree of accuracy which is constantly confirmed by astronomical observations. The time and place of eclipses and tides throughout the world are all officially noted and predicted in the Nautical Almanac; again the overall accuracy of the forecasts convinces us that the laws are valid for all such practical purposes. (2) The First Law The first law provides the definition of force which we have already quoted in Chapter One: 'force is that which tends to change the state of rest or uniform motion of a body'. It should be noted that it is the resultant force on the body which is being discussed in each case.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Newton’s first law indicates that a state of rest (zero velocity) and a state of constant velocity are completely equivalent, in the sense that neither one requires the application of a net force to sustain it. The purpose served when a net force acts on an object is not to sustain the object’s velocity, but, rather, to change it. Inertia and Mass A greater net force is required to change the velocity of some objects than of others. For instance, a net force that is just enough to cause a bicycle to pick up speed will cause only an imperceptible change in the motion of a freight train. In comparison to the bicycle, the train has a much greater tendency to remain at rest. Accordingly, we say that the train has more inertia than the bicycle. FIGURE 4.1 The arrow labeled F → represents the force that acts on (a) the football player, (b) the water skier, and (c) the cliff diver. F David Dermer/Diamond Images/Getty Images (a) F age fotostock/SuperStock (b) F Ikon Images/SuperStock (c) Scott Gardner/AP/Wide World Photos FIGURE 4.2 The game of ice hockey can give some insight into Newton’s laws of motion. 82 CHAPTER 4 Forces and Newton’s Laws of Motion Quantitatively, the inertia of an object is measured by its mass. The following definition of inertia and mass indicates why Newton’s first law is sometimes called the law of inertia: DEFINITION OF INERTIA AND MASS Inertia is the natural tendency of an object to remain at rest or in motion at a constant velocity. The mass of an object is a quantitative measure of inertia. SI Unit of Inertia and Mass: kilogram (kg) The SI unit for mass is the kilogram (kg), whereas the units in the CGS system and the BE system are the gram (g) and the slug (sl), respectively. Conversion factors between these units are given on the page facing the inside of the front cover. Interactive Figure 4.3 gives the typical masses of various objects, ranging from a penny to a supertanker.
eBook - PDF- Robert Resnick, David Halliday, Kenneth S. Krane(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
force acts. We then assign a mass m to a body by compar- ing the acceleration of that body with the acceleration of the standard body when the same force is applied to both. Finally, we develop force laws based on the properties of the body and its environment. Force thus appears in both the laws of motion (which tell us what acceleration an ob- ject will experience under the action of a given force) and in the force laws (which tell us how to calculate the force on a body in a certain environment). The laws of motion and the force laws together make up the laws of classical mechanics, as Fig. 3-1 suggests. This program of mechanics cannot be tested piecemeal. We must view it as a whole and judge its success based on the answers to two questions: (1) Does the program yield results that agree with experiment? (2) Are the force laws simple and reasonable in form? It is the crowning glory of classical mechanics that we can answer an enthusiastic “yes” to both of these questions. 3-2 NEWTON’S FIRST LAW Before Galileo’s time most philosophers thought that some influence or “force” was needed to keep a body moving. They thought that a body was in its “natural state” when it was at rest. For a body to move in a straight line at constant speed, for example, they believed that some external agent had to continually propel it; otherwise it would “naturally” stop moving. If we wanted to test these ideas experimentally, we would first have to find a way to free a body from all influ- ences of its environment or from all forces. This is hard to do, but in certain cases we can make the forces very small. If we study the motion as we make the forces smaller and smaller, we can get an idea of what the motion would be like if the external forces were truly zero. Let us place our test body — say, a block — on a rigid horizontal plane. If we let the block slide along this plane, we note that it gradually slows down and stops.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
F David Dermer/Diamond Images/Getty Images (a) F age fotostock (b) F Ikon Images/SuperStock (c) Scott Gardner/AP/Wide World Photos FIGURE 4.2 The game of ice hockey can give some insight into Newton’s laws of motion. 88 CHAPTER 4 Forces and Newton’s Laws of Motion When an object moves at a constant speed in a constant direction, its velocity is constant. Newton’s first law indicates that a state of rest (zero velocity) and a state of constant velocity are completely equivalent, in the sense that neither one requires the application of a net force to sustain it. The purpose served when a net force acts on an object is not to sustain the object’s velocity, but, rather, to change it. Inertia and Mass A greater net force is required to change the velocity of some objects than of others. For instance, a net force that is just enough to cause a bicycle to pick up speed will cause only an imperceptible change in the motion of a freight train. In comparison to the bicycle, the train has a much greater tendency to remain at rest. Accordingly, we say that the train has more inertia than the bicycle. Quantitatively, the inertia of an object is measured by its mass. The following definition of inertia and mass indicates why Newton’s first law is sometimes called the law of inertia: DEFINITION OF INERTIA AND MASS Inertia is the natural tendency of an object to remain at rest or in motion at a constant velocity. The mass of an object is a quantitative measure of inertia. SI Unit of Inertia and Mass: kilogram (kg) The SI unit for mass is the kilogram (kg), whereas the units in the CGS system and the BE system are the gram (g) and the slug (sl), respectively. Conversion factors between these units are given on the page facing the inside of the front cover. Interac- tive Figure 4.3 gives the typical masses of various objects, ranging from a penny to a supertanker.
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
The object experiences acceleration due to gravity. • Some upward resistance force from the air acts on all falling objects on Earth, so they can never truly be in free fall. Chapter 5 | Newton's Laws of Motion 253 • Careful distinctions must be made between free fall and weightlessness using the definition of weight as force due to gravity acting on an object of a certain mass. 5.5 Newton’s Third Law • Newton’s third law of motion represents a basic symmetry in nature, with an experienced force equal in magnitude and opposite in direction to an exerted force. • Two equal and opposite forces do not cancel because they act on different systems. • Action-reaction pairs include a swimmer pushing off a wall, helicopters creating lift by pushing air down, and an octopus propelling itself forward by ejecting water from its body. Rockets, airplanes, and cars are pushed forward by a thrust reaction force. • Choosing a system is an important analytical step in understanding the physics of a problem and solving it. 5.6 Common Forces • When an object rests on a surface, the surface applies a force to the object that supports the weight of the object. This supporting force acts perpendicular to and away from the surface. It is called a normal force. • When an object rests on a nonaccelerating horizontal surface, the magnitude of the normal force is equal to the weight of the object. • When an object rests on an inclined plane that makes an angle θ with the horizontal surface, the weight of the object can be resolved into components that act perpendicular and parallel to the surface of the plane. • The pulling force that acts along a stretched flexible connector, such as a rope or cable, is called tension. When a rope supports the weight of an object at rest, the tension in the rope is equal to the weight of the object. If the object is accelerating, tension is greater than weight, and if it is decelerating, tension is less than weight.
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