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Types of force?

Whitney Matthews

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Daniel King on November 18, 2019

Type of Force (and Symbol) . Description of Force Given by the, but investigated in the inertnet DIVINE CALAMA . The applied Force F of the application . Applied force is a force that is applied to an object, a person or another object. If a person is pushing a desk across the room, then there is an applied force acting upon the object. The applied force is the force exerted on the table by the part of the person. . The Force of gravity (also known as Weight) F grav . The force of gravity is the force with which the earth, moon, or other massively large object attracts another object towards itself. By definition, this is the weight of the object. All objects upon earth experience a force of gravity that is directed "downward", toward the center of the earth. The force of gravity on earth is always equal to the weight of the object according to the equation: Fgrav = m * g where g = 9.8 N/kg (on Earth) and m = mass (in kg) (Caution: do not confuse weight with mass.) . Normal force F of the standard . The normal force is the support force exerted on an object that is in contact with another stable object. For example, if a book is at rest on a surface, then the surface exerts a force upward on the book with the aim of supporting the weight of the book. On occasions, a normal force is exerted horizontally between two objects that are in contact with each other. For example, if a person leans against a wall, the wall pushes horizontally on the person. . The friction Force F frict . The friction force is the force exerted by a surface as an object moves across it or makes an effort to move through it. There are at least two types of friction force-sliding and static friction. The thought is not always the case, the friction force often opposes the motion of an object. For example, if a book slides across the surface of a desk, then the desk exerts a friction force in the opposite direction to its motion. The friction of the results of the two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces. As such, friction depends upon the nature of the two surfaces and upon the degree in which they are pressed at the same time. The maximum amount of friction force that a surface can exert upon an object can be calculated using the following formula: F frict = µ • F a standard The force of friction is discussed in more detail later in this page. . The air Resistance, the Force F of air . Air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will frequently be neglected due to its negligible magnitude (and due to the fact that it is mathematically difficult to predict its value). It is more noticeable for objects that travel at high speeds (for example, a skydiver or a downhill skier) or for objects with large surface areas. The air resistance will be discussed in more detail in Lesson 3. . The tension Force F tens . The tension force is the force which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. The tension force is directed along the length of the wire and pulls equally on objects at opposite ends of the cables. . The spring Force F of the spring . The spring force is the force exerted by a compressed or stretched spring upon any object that is connected to it. An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position. For most springs (specifically, for those who are said to obey "Law of Hooke"), the magnitude of the force is directly proportional to the amount of stretch or compression of the spring. . The confusion of Mass and Weight A few further comments should be added about the single force that is a source of much confusion to many students of physics-the force of gravity. As mentioned above, the force of gravity acting on an object is sometimes referred to as the weight of the object. Many of the physics students confuse weight with mass. The mass of an object refers to the amount of matter that contains the object; the weight of an object is the force of gravity acting on the object. The mass is related to the amount of things that is there and weight is related to the attraction of the Earth (or any other planet) upon that stuff . The mass of an object (measured in kg) will be the same, regardless of where in the universe the object is located. The mass is never altered by location, the force of gravity, the speed or even the existence of other forces. For example, a 2-kg object has a mass of 2 kg whether it is located in the Earth, the moon, or Jupiter; its mass is 2 kg if it is moving or not (at least for the purposes of our study); and its mass is 2 kg whether it is being pushed or not. On the other hand, the weight of an object (measured in Newton) will vary according to where in the universe the object. The weight depends upon which planet is exerting the force and the distance of the object from the planet. Of weight, equal to the force of gravity, depends on the value of g - the gravitational field strength. On the surface of the earth g is 9.8 N/kg (frequency of approximately 10 N/kg). On the moon's surface, g is 1.7 N/kg Go to another planet, and there will be another g value. In addition, the value of g is inversely proportional to the distance from the center of the planet. So if we were to measure g at a distance of 400 km above the surface of the earth, then we have to find the value of g less than 9.8 N/kg (the nature of The force of gravity will be discussed in more detail later in the unit of The Physics Classroom.) Always be wary of the distinction between mass and weight. It is the source of much confusion to many students of physics. Sliding versus Static Friction As mentioned above, the friction force is the force exerted by a surface as an object moves across it or makes an effort to move through it. For the purpose of our study of physics in The Physics Class, there are two types of friction, force of static friction and sliding friction. The sliding friction results when an object slides across a surface. As an example, consider pushing a box across a floor. The floor surface offers resistance to the motion of the box. We often say that the floor exerts a friction force on the box. This is an example of a sliding friction force, since the results of the sliding motion of the box. If a car slams on its brakes and skids to a stop (without abs), there is a force of sliding friction exerted upon the car tires by the roadway surface. This friction force is also a sliding friction force because the car will slide on the surface of the road. Sliding friction forces can be calculated from knowledge of the friction coefficient and the normal force exerted on the object, the surface of sliding through. The formula is: Sliding F frict = μ • F standard, The symbol represents the coefficient of friction between the two surfaces. The coefficient value depends mainly on the nature of the surfaces that are in contact with each other. For the majority of the surface of the combinations, the friction coefficients show little dependence on other variables such as the area of contact, temperature, etc, The values have been experimentally determined for a variety of surface combinations and are often tabulated in technical manuals and handbooks. The values of μ provide a measure of the relative amount of adhesion or attraction of the two surfaces to each other. The more that surface molecules tend to adhere to each other, the greater the coefficient values and the greater the friction force. Friction forces can also exist when the two surfaces are not sliding across each other. Such friction forces are referred to as static friction. Static friction occurs when the surfaces of two objects are at rest relative to one another and a force exists on one of the objects to set in motion with respect to another object. Suppose you were to push with 5-Newton of force on a large box to move it across the floor. The box can stay in place. A force of static friction that exists between surfaces of the floor and the box to prevent the box is put in motion. The force of static friction balances the force exerted on the box that the stationary box remains at rest. When exerting 5 Newton of applied force on the box, the static friction force has a magnitude of 5 Newton. Suppose that you push with 25 Newton of force on the large box and the box still remain in place. Static friction now has a magnitude of 25 Newton. Then, suppose that to increase the force to 26 Newton and the box finally budged from its resting position and set in motion throughout the floor. The box-floor surfaces were able to provide up to 25 Newton of static friction force to match your applied force. However, the two surfaces were not able to provide 26 Newton of static friction force. The amount of static friction resulting from the adhesion of any two surfaces has an upper limit. In this case, the static friction force spans the range from 0 to Newton (if there is no force on the box) 25 Newton (if you click on the box with 25 Newton of force). This relationship is often expressed as follows: F frict-static ≤ μ frict-static • F standard The symbol μ frict-static represents the coefficient of static friction between the two surfaces. As the coefficient of sliding friction, this coefficient depends on the types of surfaces that are trying to pass through each other. In general, the values of the coefficients of static friction are higher than the values of the coefficients of sliding friction for the two surfaces. Therefore, it usually takes more force to budge an object into motion than it does to maintain the motion once it has started. The meaning of each of these forces listed in the table above has to be thoroughly understood for success during this unit. Ultimately, you must be able to read a verbal description of a physical situation and know enough about these forces to recognize their presence (or absence) and the construction of a free body diagram that illustrates the relative magnitude and the direction.


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