Physics
Pulling Force
Pulling force refers to the force exerted when an object is being pulled in a particular direction. It is a type of mechanical force that acts in the opposite direction to the force applied to pull an object. Pulling force is a vector quantity, meaning it has both magnitude and direction.
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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.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 6 Force Forces are also described as a push or pull on an object. They can be due to phenomena such as gravity, magnetism, or anything else that might cause a mass to accelerate. In physics, a force is any influence that causes a free body to undergo an acceleration. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a vector quantity. Newton's second law, F=ma, can be formulated to state that an object with a constant mass will accelerate in proportion to the net force acting upon and in inverse proportion to its mass, an approximation which breaks down near the speed of light. Newton's original formulation is exact, and does not break down: this version states that the net force acting upon an object is equal to the rate at which its momentum changes. Related concepts to accelerating forces include thrust, increasing the velocity of the object, drag, decreasing the velocity of any object, and torque, causing changes in rotational speed about an axis. Forces which do not act uniformly on all parts of a body ________________________ WORLD TECHNOLOGIES ________________________ will also cause mechanical stresses, a technical term for influences which cause deformation of matter. While mechanical stress can remain embedded in a solid object, gradually deforming it, mechanical stress in a fluid determines changes in its pressure and volume.
eBook - PDFQuestioning the Universe
Concepts in Physics
- Ahren Sadoff(Author)
- 2008(Publication Date)
- Chapman and Hall/CRC(Publisher)
23 4 Forces 4.1 THE FUNDAMENTAL FORCES What is a force? One answer is that it is a push or a pull. A better answer, that we will find to be more useful, is that it is an interaction between two or more objects. For most of our discussion, two objects will suffice. Forces are no strangers to us since we interact with all sorts of things every day. Below is a list of forces I have compiled. Before reading my list, it would be instruc-tive for you to take out a piece of paper and make your own list. Hopefully you will come up with some not on my list. Gravity Electric Weak nuclear Strong nuclear Centrifugal Magnetic Centripetal Friction Wind force Contact force (between surfaces) Muscular force Chemical Atomic I am sure you have noticed that my list is arranged in columns or categories. Let us look at the last column first. Both items are, in fact, not forces at all, but adjec-tives describing the action of a particular force. A centrifugal force is any force that is directed outward from the center of a curve when an object is traveling in curved motion. Similarly, a centripetal force acts inward toward the center of the curve. Gravity is usually the force most people list first, as I have. It, of course, is very important to us since it keeps us bound to the earth and the earth to the sun. The second column contains many familiar forces under one heading. Why? Because all these seemingly different forces are all due to only one force. Electric and magnetic are not separate forces, but just different manifestations of what is known as the electromagnetic force (we will discuss this in more detail shortly). The force that holds the atom together is not some special new force, but is just due to the electri-cal attraction of the negatively charged electrons to the positively charged protons in the nucleus. Similarly, different atoms interact by the attraction or repulsion of the electrons and protons in one atom acting on the electrons and protons of another atom.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
15. A person has a choice of either pushing or pulling a sled at a constant velocity, as CYU Figure 4.2 illustrates. Friction is present. If the angle θ is the same in both cases, does it require less force to push or to pull the sled? θ θ CYU FIGURE 4.2 16. A box has a weight of 150 N and is being pulled across a horizontal floor by a force that has a mag- nitude of 110 N. The Pulling Force can point horizontally, or it can point above the horizontal at an angle θ. When the Pulling Force points horizontally, the kinetic frictional force acting on the box is twice as large as when the Pulling Force points at the angle θ. Find θ. 17. A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is (a) stationary, (b) accelerating upward, and (c) accelerating downward. Rank the forces required in these three situations in ascending order—that is, smallest first. 4.10 The Tension Force Forces are often applied by means of cables or ropes that are used to pull an object. For instance, Figure 4.25a shows a force T → being applied to the right end of a rope attached to a box. Each particle in the rope in turn applies a force to its neighbor. As a result, the force is applied to the box, as part b of the drawing shows. In situations such as that in Figure 4.25, we say that the force T → is applied to the box be- cause of the tension in the rope, meaning that the tension and the force applied to the box have the same magnitude. However, the word “tension” is commonly used to mean the tendency of the rope to be pulled apart. To see the relationship between these two uses of the word “tension,” consider the left end of the rope, which applies the force T → to the box. In accordance with Newton’s third law, the box applies a reaction force to the rope. The reaction force has the same magnitude as T → but is oppositely directed. In other words, a force − T → acts on the left end of the rope.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 2 Force Forces are also described as a push or pull on an object. They can be due to phenomena such as gravity, magnetism, or anything that might cause a mass to accelerate. Force SI symbol: F SI unit: newton Derivations from other quantities: F = m · a In physics, a force is any influence that causes a free body to undergo a change in speed, a change in direction, or a change in shape. Force can also be described by intuitive concepts such as a push or pull that can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate, or which can cause a flexible object to deform. A force has both magnitude and direction, making it a vector quantity. Newton's second law, F=ma, can be formulated to state that an object with a constant mass will accelerate in proportion to the net force acting upon and in inverse proportion to its mass, an approximation which breaks down near the speed of light. Newton's original formulation is exact, and does not break down: this version states ________________________ WORLD TECHNOLOGIES ________________________ that the net force acting upon an object is equal to the rate at which its momentum changes. Related concepts to accelerating forces include thrust, increasing the velocity of the object, drag, decreasing the velocity of any object, and torque, causing changes in rotational speed about an axis. Forces which do not act uniformly on all parts of a body will also cause mechanical stresses, a technical term for influences which cause deformation of matter. While mechanical stress can remain embedded in a solid object, gradually deforming it, mechanical stress in a fluid determines changes in its pressure and volume.
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)
In reaction, the bumper pushes back on the tow bar. The reaction force is used by the mechanism in the tow bar to ‘push a brake pedal’ for the trailer. FIGURE 4.8 Some rental trailers include an automatic brake‐actuating mechanism. Mechanism for actuating trailer brakes 4.6 Types of forces: an overview LEARNING OBJECTIVE 4.6 Identify types of forces. Newton’s three laws of motion make it clear that forces play a central role in determining the motion of an object. In the next four sections some common forces will be discussed: the gravitational force (section 4.7), the normal force (section 4.8), frictional forces (section 4.9), and the tension force (section 4.10). In later chapters, we will encounter still others, such as electric and magnetic forces. It is important to realise that Newton’s second law is always valid, regardless of which of these forces may act on an object. One does not have a different law for every type of common force. Thus, we need only to determine what forces are acting on an object, add them together to form the net force, and then use Newton’s second law to determine the object’s acceleration. In nature there are two general types of forces, fundamental and nonfundamental. Fundamental forces are the ones that are truly unique, in the sense that all other forces can be explained in terms of them. Only three fundamental forces have been discovered: 1. gravitational force 2. strong nuclear force 3. electroweak force. The gravitational force is discussed in the next section. The strong nuclear force plays a primary role in the stability of the nucleus of the atom (see section 31.2). The electroweak force is a single force that manifests itself in two ways (see section 32.6). One manifestation is the electromagnetic force that elec- trically charged particles exert on one another (see sections 18.5, 21.2, and 21.8).
eBook - PDFApplied Mechanics
Made Simple
- George E. Drabble(Author)
- 2013(Publication Date)
- Made Simple(Publisher)
The first law gives us a definition of force: force is something which, by itself, produces an acceleration. This is the definition of force, and is clearly more satisfactory than the 'push or pull' we have had to accept so far. It only gives us a qualitative definition: it does not tell us how to measure force, but we shall find the answer to this problem in the second law. Let us now see how general the first law is in its application, and how it must have appeared to cut right across contemporary beliefs. It is natural to assume that a body which is not acted upon by a force would be in a state of rest: it is not so obvious to assume a possible state of motion in a straight line. All terrestrial experience of Newton's day must have pointed to other con-clusions. All bodies on the Earth, if set moving, came 'naturally' to rest. On the other hand, bodies apparently free from earthly interference (planets, for instance) were known to move in approximately circular paths. From the time of the Greeks, one school of thought accepted the 'natural' motion of bodies as circular. We now know that earth-bound bodies are subjected to fric-tional force, and that planets are subjected to gravitational force: both of 40 Applied Mechanics Made Simple these forces cause departure from straight-line uniform motion. In fact, perhaps the most exasperating aspect of Newton's theories is that no body ever observed has a 'natural' motion unaffected by force. There is an intri-guing and amusing dialogue on this topic between Newton and the artist, Kneller in G. B. Shaw's play, 'In Good King Charles's Golden Days'. It is perhaps typical of Newton's genius that he was able to perceive, without the benefit of direct observation, what the unforced motion of a body would be. Present-day students have less difficulty with this idea than those of an earlier age.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
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. 4.10 The Tension Force The word “tension” is commonly used to mean the tendency of a rope to be pulled apart due to forces that are applied at each end. Because of tension, a rope transmits a force from one end to the other. When a rope is accelerating, the force is transmitted undiminished only if the rope is massless. 4.11 Equilibrium Applications of Newton’s Laws of Motion An object is in equilibrium when the object has zero acceleration, or, in other words, when it moves at a constant velocity. The constant velocity may be zero, in which case the object is stationary. The sum of the forces that act on an object in equilibrium is zero. Under equilibrium conditions in two dimensions, the separate sums of the force components in the x direction and in the y direction must each be zero, as in Equations 4.9a and 4.9b. 4.12 Nonequilibrium Applications of Newton’s Laws of Motion If an object is not in equilibrium, then Newton’s second law, as expressed in Equations 4.2a and 4.2b, must be used to account for the acceleration. S F B 5 ma B (4.1) SF x 5 ma x (4.2a) SF y 5 ma y (4.2b) F 5 G m 1 m 2 r 2 (4.3) W 5 mg (4.5) Apparent weight 5 mg 1 ma (4.6) f s MAX 5 m s F N (4.7) f k 5 m k F N (4.8) SF x 5 0 (4.9a) SF y 5 0 (4.9b) SF x 5 ma x (4.2a) SF y 5 ma y (4.2b) FOCUS ON CONCEPTS Note to Instructors: The numbering of the questions shown here reflects the fact that they are only a representative subset of the total number that are available online. However, all of the questions are available for assignment via an online homework management program such as WileyPLUS or WebAssign. Section 4.2 Newton’s First Law of Motion 1. An object is moving at a constant velocity. All but one of the following statements could be true.
eBook - PDF- Paul Peter Urone, Roger Hinrichs(Authors)
- 2012(Publication Date)
- Openstax(Publisher)
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 . When a rope supports the weight of an object that is at rest, the tension in the rope is equal to the weight of the object: T = mg. • In any inertial frame of reference (one that is not accelerated or rotated), Newton’s laws have the simple forms given in this chapter and all forces are real forces having a physical origin. 4.6 Problem-Solving Strategies • To solve problems involving Newton’s laws of motion, follow the procedure described: 1. Draw a sketch of the problem. 2. Identify known and unknown quantities, and identify the system of interest. Draw a free-body diagram, which is a sketch showing all of the forces acting on an object. The object is represented by a dot, and the forces are represented by vectors extending in different directions from the dot. If vectors act in directions that are not horizontal or vertical, resolve the vectors into horizontal and vertical components and draw them on the free-body diagram. 3. Write Newton’s second law in the horizontal and vertical directions and add the forces acting on the object. If the object does not accelerate in a particular direction (for example, the x -direction) then F net x = 0 . If the object does accelerate in that direction, F net x = ma . 4. Check your answer. Is the answer reasonable? Are the units correct? 4.7 Further Applications of Newton’s Laws of Motion • Newton’s laws of motion can be applied in numerous situations to solve problems of motion. • Some problems will contain multiple force vectors acting in different directions on an object. Be sure to draw diagrams, resolve all force vectors into horizontal and vertical components, and draw a free-body diagram. Always analyze the direction in which an object accelerates so that you can determine whether F net = ma or F net = 0 .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
For example, consider a system consisting of an object that is being lowered vertically by a string with tension, T, at a constant velocity. The system has a constant velocity and is therefore in equilibrium because the tension in the string (which is pulling up on the object) is equal to the force of gravity, mg, which is pulling down on the object. ________________________ WORLD TECHNOLOGIES ________________________ System under net force A system has a net force when an unbalanced force is exerted on it, in other words the sum of all forces is not zero. Acceleration and net force always exist together. For example consider the same system as above but suppose the object is now being lowered with an increasing velocity downwards (positive acceleration) therefore there exists a net force somewhere in the system. In this case negative acceleration would indicate that | mg | > | T |. Strings in modern physics String-like objects in relativistic theories, such as the strings used in some models of interactions between quarks, or those used in the modern string theory, also possess tension. These strings are analyzed in terms of their world sheet, and the energy is then typically proportional to the length of the string. As a result, the tension in such strings is independent of the amount of stretching. 4. Pressure Pressure (the symbol: P ) is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure. Definition Pressure is an effect which occurs when a force is applied on a surface. Pressure is the amount of force acting on a unit area. The symbol of pressure is P . ________________________ WORLD TECHNOLOGIES ________________________ Formula Conjugate variables of thermodynamics Pressure Volume (Stress) (Strain) Temperature Entropy Chemical potential Particle number Mathematically: where: P is the pressure, F is the normal force, A is the area.
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