Physics
Normal Force
The normal force is the force exerted by a surface to support the weight of an object resting on it. It acts perpendicular to the surface and prevents objects from passing through it. In equilibrium, the normal force is equal in magnitude and opposite in direction to the force of gravity acting on the object.
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11 Key excerpts on "Normal Force"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 4 Non-Fundamental Forces 1. Normal Force F N represents the Normal Force In physics, the Normal Force (occasionally N ) is the component, perpendicular to the surface of contact, of the contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall. In a static situation it is just enough to balance the forces acting on the object, such as the force with which the object pushes against the surface and friction. In another common situation, if an object hits the surface with some speed, and the surface can withstand it, the Normal Force provides for a rapid deceleration, with the speed depending on the flexibility of the surface. If the object is soft, the part on the side of the surface will tend to decelerate more rapidly, the part on the other side can do that more gradually, and the layer in between is compressed, deforming the object. The Normal Force is one of the basic concepts in mechanics, the branch of physics concerned with the behaviour of physical bodies when subjected to forces or displa-cements. ________________________ WORLD TECHNOLOGIES ________________________ Equations Weight ( W ), the frictional force ( F r ), and the Normal Force ( F n ) impacting a cube. Weight is mass ( m ) multiplied by gravity ( g ). In a simple case such as an object resting upon a table, the Normal Force on the object is equal but in opposite direction to the gravitational force applied on the object (or the weight of the object), that is, N = mg , where m is mass, and g is the gravitational field strength (about 9.81 Newtons/kilogram on Earth). The Normal Force here represents the force applied by the table against the object that prevents it from sinking through the table, and requires that the table is sturdy enough to deliver this Normal Force without breaking.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 4 Non-Fundamental Forces 1. Normal Force F N represents the Normal Force In physics, the Normal Force (occasionally N ) is the component, perpendicular to the surface of contact, of the contact force exerted by, for example, the surface of a floor or wall, on an object, preventing the object from entering the floor or wall. In a static situation it is just enough to balance the forces acting on the object, such as the force with which the object pushes against the surface and friction. In another common situation, if an object hits the surface with some speed, and the surface can withstand it, the Normal Force provides for a rapid deceleration, with the speed depending on the flexibility of the surface. If the object is soft, the part on the side of the surface will tend to decelerate more rapidly, the part on the other side can do that more gradually, and the layer in between is compressed, deforming the object. The Normal Force is one of the basic concepts in mechanics, the branch of physics concerned with the behaviour of physical bodies when subjected to forces or dis-placements. ________________________ WORLD TECHNOLOGIES ________________________ Equations Weight ( W ), the frictional force ( F r ), and the Normal Force ( F n ) impacting a cube. Weight is mass ( m ) multiplied by gravity ( g ). In a simple case such as an object resting upon a table, the Normal Force on the object is equal but in opposite direction to the gravitational force applied on the object (or the weight of the object), that is, N = mg , where m is mass, and g is the gravitational field strength (about 9.81 Newtons/kilogram on Earth). The Normal Force here represents the force applied by the table against the object that prevents it from sinking through the table, and requires that the table is sturdy enough to deliver this Normal Force without breaking.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
The next section discusses the component that acts parallel to the surface. The perpendicular component is called the Normal Force. Definition of the Normal Force The Normal Force F N B is one component of the force that a surface exerts on an object with which it is in contact—namely, the component that is perpendicular to the surface. Figure 4.13 shows a block resting on a horizontal table and identifies the two forces that act on the block, the weight W B and the Normal Force F N B . To understand how an inan- imate object, such as a tabletop, can exert a Normal Force, think about what happens when you sit on a mattress. Your weight causes the springs in the mattress to compress. As a result, the compressed springs exert an upward force (the Normal Force) on you. In a similar manner, the weight of the block causes invisible “atomic springs” in the surface of the table to compress, thus producing a Normal Force on the block. Newton’s third law plays an important role in connection with the Normal Force. In Figure 4.13, for instance, the block exerts a force on the table by pressing down on it. Con- sistent with the third law, the table exerts an oppositely directed force of equal magnitude on the block. This reaction force is the Normal Force. The magnitude of the Normal Force indicates how hard the two objects press against each other. If an object is resting on a horizontal surface and there are no vertically acting forces except the object’s weight and the Normal Force, the magnitudes of these two forces are equal; that is, F N 5 W. This is the situation in Figure 4.13. The weight must be balanced by the Normal Force for the object to remain at rest on the table. If the magnitudes of these forces were not equal, there would be a net force acting on the block, and the block would accelerate either upward or downward, in accord with Newton’s second law.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
Figure 4.13 shows a block resting on a horizontal table and identifies the two forces that act on the block, the weight W → and the Normal Force F N → . To understand how an inanimate object, such as a tabletop, can exert a Normal Force, think about what happens when you sit on a mattress. Your weight causes the springs in the mattress to compress. As a result, the compressed springs exert an upward force (the Normal Force) on you. In a similar manner, the weight of the block causes invisible “atomic springs” in the surface of the table to compress, thus producing a Normal Force on the block. Newton’s third law plays an important role in connection with the Normal Force. In Figure 4.13, for instance, the block exerts a force on the table by pressing down on it. Consistent with the third law, the table exerts an oppositely directed force of equal magnitude on the block. This reaction force is the Normal Force. The magnitude of the Normal Force indicates how hard the two objects press against each other. If an object is resting on a horizontal surface and there are no vertically acting forces except the object’s weight and the Normal Force, the magnitudes of these two forces are equal; that is, F N = W. This is the situation in Figure 4.13. The weight must be balanced by the Normal Force for the object F N W FIGURE 4.13 Two forces act on the block, its weight W → and the Normal Force F N → exerted by the surface of the table. 4.8 The Normal Force 93 to remain at rest on the table. If the magnitudes of these forces were not equal, there would be a net force acting on the block, and the block would accelerate either upward or downward, in accord with Newton’s second law. If other forces in addition to W → and F N → act in the vertical direction, the magnitudes of the Normal Force and the weight are no longer equal. In Figure 4.14a, for instance, a box whose weight is 15 N is being pushed downward against a table.
eBook - PDF- Robert Resnick, David Halliday, Kenneth S. Krane(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
This force is the Normal Force ex- erted on the book by the table. In this sense, the word “nor- mal” means “perpendicular”— the Normal Force exerted by a surface is always perpendicular to (or normal to) the surface. Even though the Normal Force shown in the free-body di- agram of Fig. 5-6b is equal and opposite to the weight, it is not the reaction force to the weight. The weight is the force of the Earth on the book, and its reaction force is the force exerted by the book on the Earth. The reaction force to the Normal Force is the downward force exerted by the book on the table; it would appear in a free-body diagram of the table. Remember that the action – reaction pairs of Newton’s third law never act on the same body, so the forces N and W that act on the book cannot be an action – reaction pair. If someone placed a hand on top of the book and pushed downward with a force P, the book would remain at rest. For an acceleration of zero, the net force on the book must be zero and so the total downward force must equal the total upward force N. The Normal Force must therefore increase as P increases, since Eventually, P could become large enough to exceed the ability of the N W P. W P T m(g a y ) (2.4 kg)(9.8 m/s 2 3.2 m/s 2 ) 31 N. a y 3.2 m/s 2 , T mg (2.4 kg)(9.8 m/s 2 ) 24 N. a y 0 table to provide the upward Normal Force, and the book would break through the tabletop. Tension and Normal Forces are examples of contact forces, in which one body exerts a force on another because of the contact between them. These forces originate with the atoms of each body — each atom exerts a force on its neighbor (which may be an atom of another body). A con- tact force can be maintained only if it does not exceed the interatomic forces within either of the bodies; otherwise the binding between atoms can be overcome and the string or the surface will split into pieces.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
For two particles that are separated by a distance r and have masses m 1 and m 2 , the law states that the magnitude of this attractive force is as given in Equation 4.3. The direction of this force lies along the line between the particles. The con- stant G has a value of G 5 6.674 3 10 211 N ? m 2 /kg 2 and is called the universal gravitational constant. The weight W of an object on or above the earth is the gravitational force that the earth exerts on the object and can be calculated from the mass m of the object and the magnitude g of the acceleration due to the earth’s gravity, according to Equation 4.5. 4.8 The Normal Force The Normal Force F N B is one component of the force that a surface exerts on an object with which it is in contact—namely, the component that is perpendicular to the surface. The apparent weight is the force that an object exerts on the platform of a scale and may be larger or smaller than the true weight mg if the object and the scale have an acceleration a (1 if upward, 2 if downward). The apparent weight is given by Equation 4.6. 4.9 Static and Kinetic Frictional Forces A surface exerts a force on an object with which it is in contact. The component of the force perpendicular to the surface is called the Normal Force. The component parallel to the surface is called friction. The force of static friction between two surfaces opposes any impending relative motion of the surfaces. The magnitude of the static frictional force depends on the magnitude of the applied force and can assume any value up to the maximum specified in Equation 4.7, where m s is the coefficient of static friction and F N is the magnitude of the Normal Force. The force of kinetic friction between two surfaces sliding against one another opposes the relative motion of the surfaces. This force has a magnitude given by Equation 4.8, where m k is the coefficient of kinetic friction.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
CHAPTER4 Forces and Newton's Laws of Motion PREVIEW In this chapter you will begin the study of dynamics, that branch of physics which explains why objects accelerate. You will be introduced to the concept of force, and study Newton's laws of motion, which apply to all forces that occur in nature. You will learn how to construct free-body diagrams, and use them to analyze systems subject to such forces as gravity and friction. You will also apply Newton's laws of motion to solve a number of different problems. The applications will include both equilibrium and non-equilibrium problems. QUICK REFERENCE Important Terms Force The push or pull required to change the state of motion of an object, as defined by Newton's second law. It is a vector quantity with units of newtons (N), dynes (dyn), or pounds (lb ). Inertia The natural tendency of an object to remain at rest or in uniform motion at a constant speed in a straight line. Mass A quantitative measure of inertia. Units are kilograms (kg), grams (g), or slugs (sl). Inertial Reference Frame A reference frame in which Newton's law of inertia is valid. Free-Body Diagram A vector diagram that represents all of the forces acting on an object. Gravitational Force The force of attraction that every particle of mass in the universe exerts on every other particle. Weight The gravitational force exerted by the earth (or some other large astronomical body) on an object. Normal Force One component of the force that a surface exerts on an object with which it is in contact. This component is directed normal, or perpendicular, to the surface. Friction The force that an object encounters when it moves or attempts to move along a surface. It is always directed parallel to the surface in question. Tension The tendency of a rope (or similar object) to be pulled apart due to the forces that are applied at either end. Equilibrium The state an object is in if it has zero acceleration.
eBook - PDF- Paul Peter Urone, Roger Hinrichs(Authors)
- 2012(Publication Date)
- Openstax(Publisher)
• In equation form, Newton’s second law of motion is a = F net m . • This is often written in the more familiar form: F net = ma . • The weight w of an object is defined as the force of gravity acting on an object of mass m . The object experiences an acceleration due to gravity g : 164 Chapter 4 | Dynamics: Force and Newton's Laws of Motion This OpenStax book is available for free at http://cnx.org/content/col11406/1.9 w = mg. • If the only force acting on an object is due to gravity, the object is in free fall. • Friction is a force that opposes the motion past each other of objects that are touching. 4.4 Newton’s Third Law of Motion: Symmetry in Forces • Newton’s third law of motion represents a basic symmetry in nature. It states: 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 the first body exerts. • A thrust is a reaction force that pushes a body forward in response to a backward force. Rockets, airplanes, and cars are pushed forward by a thrust reaction force. 4.5 Normal, Tension, and Other Examples of Forces • When objects rest 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, N . • When objects rest on a non-accelerating horizontal surface, the magnitude of the Normal Force is equal to the weight of the object: N = mg. • When objects rest 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 ( w ⊥ ) and parallel ( w ∥ ) to the surface of the plane. These components can be calculated using: w ∥ = w sin (θ) = mg sin (θ) w ⊥ = w cos (θ) = mg cos (θ). • The pulling force that acts along a stretched flexible connector, such as a rope or cable, is called tension, T .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
When dealing with an extense body, it is also necessary that the net torque in it is 0. There are two kinds of equilibrium: static equilibrium and dynamic equilibrium. Static equilibrium Static equilibrium was understood well before the invention of classical mechanics. Objects which are at rest have zero net force acting on them. The simplest case of static equilibrium occurs when two forces are equal in magnitude but opposite in direction. For example, an object on a level surface is pulled (attracted) downward toward the center of the Earth by the force of gravity. At the same time, surface forces resist the downward force with equal upward force (called the Normal Force). The situation is one of zero net force and no acceleration. Pushing against an object on a frictional surface can result in a situation where the object does not move because the applied force is opposed by static friction, generated between the object and the table surface. For a situation with no movement, the static friction force exactly balances the applied force resulting in no acceleration. The static friction increases or decreases in response to the applied force up to an upper limit determined by the characteristics of the contact between the surface and the object. A static equilibrium between two forces is the most usual way of measuring forces, using simple devices such as weighing scales and spring balances. For example, an object suspended on a vertical spring scale experiences the force of gravity acting on the object balanced by a force applied by the spring reaction force which equals object's weight. Using such tools, some quantitative force laws were discovered: that the force of gravity is proportional to volume for objects of constant density (widely exploited for millennia to define standard weights); Archimedes' principle for buoyancy; Archimedes' analysis of the lever; Boyle's law for gas pressure; and Hooke's law for springs.
eBook - PDF- Stephen Lee(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
Forces and Newton’s laws of motion Nature to him was an open book. He stands before us, strong, certain and alone. Einstein on Newton 2.1 Force diagrams The picture shows a crate of medical supplies being dropped into a remote area by parachute. What forces are acting on the crate of supplies and the parachute? One force which acts on every object near the earth’s surface is its own weight . This is the force of gravity pulling it towards the centre of the earth. The weight of the crate acts on the crate and the weight of the parachute acts on the parachute. The parachute is designed to make use of air resistance . A resistance force is present whenever a solid object moves through a liquid or gas. It acts in the opposite direction to the motion and depends on the speed of the object. The crate also experiences air resistance, but to a lesser extent than the parachute. Other forces are the tensions in the guy lines attaching the crate to the parachute. These pull upwards on the crate and downwards on the parachute. All these forces can be shown most clearly if you draw force diagrams for the crate and the parachute. 2 Figure 2.1: Forces acting on the crate Figure 2.2: Forces acting on the parachute Force diagrams are essential for the understanding of most mechanical situations. A force is a vector: it has a magnitude, or size, and a direction. It also has a line of action . This line often passes through a point of particular interest. Any force diagram should show clearly ● the direction of the force ● the magnitude of the force ● the line of action. In figures 2.1 and 2.2 each force is shown by an arrow along its line of action. The air resistance has been depicted by a lot of separate arrows but this is not very satisfactory. It is much better if the combined effect can be shown by one arrow. When you have learned more about vectors, you will see how the tensions in the guy lines can also be combined into one force if you wish.
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)
CHAPTER 4 Forces and Newton’s laws of motion 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. INTRODUCTION The Wellington Cable Car has been carrying passengers high above the city for more than a century. Its funicular design sees separate cars traverse the straight inclined track from opposite ends. Each car’s weight balances the other, effectively neutralising the effect of gravity pulling down the 1 in 5 slope. In this way, the centrally located driving wheel only has to pull against the much smaller forces of friction and rolling resistance over the 600-metre journey. In this chapter we examine the relationship between forces and Newton’s laws of motion, and how these apply in clever designs such as a funicular railway. 1 4.1 The concepts of force and mass LEARNING OBJECTIVE 4.1 Discuss the concepts of force and mass. In common usage, a force is a push or a pull, as the examples in figure 4.1 illustrate. In football, a player tackles against his opponent. The tow bar attached to a speeding boat pulls a water skier. Forces such as those that push against the football player or pull the skier are called contact forces, because they arise from the physical contact between two objects. There are circumstances, however, in which two objects exert forces on one another even though they are not touching. Such forces are referred to as noncontact forces or action‐at‐a‐distance forces.
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