Physics
Mechanical Power
Mechanical power refers to the rate at which work is done or energy is transferred in a mechanical system. It is the product of force and velocity, representing the amount of work done per unit of time. In physics, mechanical power is measured in watts and is a fundamental concept in understanding the performance of machines and mechanical systems.
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6 Key excerpts on "Mechanical Power"
eBook - ePub- Jeffrey W. Bloom(Author)
- 2010(Publication Date)
- Routledge(Publisher)
This loss of energy to systems is important in our understandings of energy in ecological systems, which was discussed in Section 3. Work and Power Work, from a physics perspective, involves using energy to apply a force to move some object a specific distance. Work equals force times distance: (W = f × d). The most common unit that is used for work is a joule, named after James Joule (1818–1889), a British physicist: 1 joule = the force of 1 Newton applied over a distance of 1 meter. Work is involved in our walking and running, in driving, moving furniture, lifting weights, and all kinds of activities that require moving some sort of object a distance in some direction. • Example: You push a box 5 m across the floor using a 20 Newton force: REMEMBER: 1 Newton = mass × 1 m/sec 2 20 N × 5 m = 100 joules Let’s say this took you 6 seconds to complete. If you repeated this task in 3 seconds, it will still be the same amount of work, but you will have used twice as much power, which brings us to the next concept. Power has to do with increasing the speed at which work is done. The term watt (named after James Watt, a Scottish inventor 1736–1819) is used as the unit for power that has to do with the speed with which work is done. Although we commonly associate the term “watt” with the power of light bulbs, it is the scientific term used for power in general. The other term commonly used to describe power, especially in cars and tools with motors, is horsepower. Interestingly, the term “horsepower” was also coined by James Watt. He found that when experimenting with horses, his horses were able to pull 22,000 lb of coal the distance of 1 ft in 1 minute, but later changed it to 33,000 ft-pounds per minute. One horsepower is equivalent to the electrical horsepower of 746 watts
eBook - PDF- Michael Brumbach(Author)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Power is a measurement of the rate of doing work. The amount of work can be calculated by the formula, Work 5 Force 3 Dis-tance (W 5 FD), where the force is measured in pounds (or kilograms) and the distance is measured in feet (or meters). To determine the power a machine must de-liver, it is necessary to know the speed at which the work must be accomplished. The formula for power is Power 5 Work/Time (P 5 W/T), where work is measured in foot-pounds and time is measured in minutes (min). Horsepower Horsepower (hp) is the common unit of measure-ment of Mechanical Power in the English system. In early times, water was pumped from mines by horses pulling and turning a wheel at the end of a shaft to drive a pump. Later, horses were replaced by the steam engine. Steam engines are rated as having the power of a certain number of horses (horsepower). It was determined that an aver-age horse could do work at the rate of 33,000 foot-pounds (44,740 joules) per minute. This means that the average horse can move 1000 pounds (453.6 ki-lograms) through 33 feet (10.058 meters) in 1 min-ute. The mathematical formula for horsepower is hp 5 ft 1b / min 33,000 (Eq. 3.1) Example 1 A machine can place 50,000 lb (22,680 kg) of scrap metal onto a truck 10 ft (3.048 m) high in 5 min. What horsepower is the machine capable of delivering? P I E FIGURE 3–1 Power law triangle. Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 30 CHAPTER 3 Combining like terms gives: P 5 E 2 R This results in Equation 3.3. Equation 3.4 is also a combination of two for-mulas.
eBook - PDF- Stephen Lee(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
Energy, work and power I like work: it fascinates me. I can sit and look at it for hours. Jerome K. Jerome 9.1 Energy and momentum When describing the motion of objects in everyday language the words energy and momentum are often used quite loosely and sometimes no distinction is made between them. In mechanics they must be defined precisely. For an object of mass m moving with velocity v : ● Kinetic energy 1 2 mv 2 (this is the energy it has due to its motion) ● Momentum m v . Notice that kinetic energy is a scalar quantity with magnitude only, but momentum is a vector in the same direction as the velocity. Both the kinetic energy and the momentum are liable to change when a force acts on a body and you will learn more about how the energy is changed in this chapter. You will meet momentum again in Chapter 10. Q UESTION 9.1 This is a picture of a perpetual motion machine. What does this term mean and will this one work? 9 M C Escher’s ‘Waterfall’ © 2000 Cordon Art B.V. – Baarn – Holland. All rights reserved. 9.2 Work and energy In everyday life you encounter many forms of energy such as heat, light, electricity and sound. You are familiar with the conversion of one form of energy to another: from chemical energy stored in wood to heat energy when you burn it; from electrical energy to the energy of a train’s motion, and so on. The S.I. unit for energy is the joule, J. Mechanical energy and work In mechanics two forms of energy are particularly important. Kinetic energy is the energy which a body possesses because of its motion. ● The kinetic energy of a moving object 1 2 mass ( speed ) 2 . Potential energy is the energy which a body possesses because of its position. It may be thought of as stored energy which can be converted into kinetic or other forms of energy. You will meet this again on page 208. The energy of an object is usually changed when it is acted on by a force.
eBook - PDF- William Bolton(Author)
- 2016(Publication Date)
- Newnes(Publisher)
Energy 187 Machines A machine can be defined as a mechanical device which enables an effort force to be magnified or reduced or applied in a more convenient line of action, or the displacement of the point of application of a force to be magnified or reduced. The term effort is used for the input force, the term load for the output force. Whatever the form of the machine, energy is conserved. The force ratio or mechanical advantage is defined as the ratio of the load to effort: force ratio MA = effort The movement ratio or velocity ratio is defined as the ratio of the distance moved by the effort to the distance moved by the load: .· wr» distance moved by effort movement ratio VR = distance moved by load For an ideal machine where there are no frictional forces, the work done by the effort must equal the work done on the load, i.e. effort x distance moved by effort = load x distance moved by load Rearranging this gives load _ distance moved by effort effort distance moved by load MA = VR For a non-ideal machine there are some losses due to friction. The efficiency is defined as the ratio of the useful work done on the load to the work done by the effort: rc . . useful work done on the load efficiency = — work done by the effort The following are some examples of machines. Levers A lever can be used to change the size and/or the line of action of a force. There are three types of lever. One has the effort and load on opposite sides of the fulcrum (Figure 12.3a), e.g. scissors and pliers. Another has the effort and load on the same side of the fulcrum but with the effort at the greater distance (Figure 12.3b), e.g. a wheelbarrow. The third has the effort and load on the same side of the fulcrum but with the load at the greater distance (Figure 12.3c), e.g.
eBook - ePub- William Bolton(Author)
- 2012(Publication Date)
- Routledge(Publisher)
5 Energy transfer5.1 IntroductionThis chapter is concerned with the energy transfers that can occur with mechanical systems. Energy can be transferred from one form to another by work being done or by heat transfer. Here we restrict the discussion to transfers involving work. There are many forms that energy can take and in this chapter potential energy, linear and angular kinetic energy and strain energy are discussed and the principles applied to the solution of mechanical system problems.5.1.1 Conservation of energyThere is a basic principle that is used in all discussions of energy and that is that energy is never lost, it is only transformed from one form to another or transferred from one object to another. This is the principle of the conservation of energy. In any process we never increase the total amount of energy, all we do is transform it from one form to another.5.2 WorkThe principle of the conservation of energy is that energy is never created or lost but only converted from one form to another. In all such conversions, the total amount of energy remains constant.Work is said to be done when the energy transfer takes place as a result of a force pushing something through a distance (Figure 5.1 ), the amount of energy transferred W being the product of the force F and the displacement s of the point of application of the force in the direction of the force.Figure 5.1 WorkWith force in newtons and distance in metres, the unit of work is the joule (J) with 1 J being 1 N m.Work done by a constant force W = Fs [1] Consider the work done by a force F when the resulting displacement s is at some angle 0 to the force (Figure 5.2 ). We can look at this in two equivalent ways. We can consider the displacement in the direction of the force F is s cos θ and so the work done is:work done = F × s cos θ [2] Figure 5.2 An oblique forceAlternatively, we can consider the force component acting in the direction of the displacement. The force can be resolved into two components, namely F cos θ in the direction of the displacement and F sin θ at right angles to it. There is no displacement in the direction of the F sin θ component and so it does no work. Hence the work done by the oblique force is solely due to the F cos θ
- Alexander V. Dimitrov(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
2Conversion of Thermal Energy into Mechanical Work (Thermal Engines)Energy-related (power) technologies may be treated as a combination of engineering-technical methods of energy and work conversion employed to facilitate human life. They are divided into two main groups. The first group comprises technologies of heat conversion into another type of energy (mechanical, electrical, electromagnetic, etc.) while the second one comprises technologies of heat transfer, accumulation, and regeneration. Each thermal technology discussed herein will be illustrated by specific physical schemes and devices. We shall consider them in the following order:•Technologies of mechanical work performance (so called thermomechanical technologies) •Technologies of generation of electrical energy (thermoelectric technologies) •Technologies of heat transformation (regeneration and recuperation) •Technologies of heat transfer and collection (transfer and accumulation) •Technologies creating comfortable environment (air conditioning and ventilation)Thus, we will treat a certain technology as an object of study of respective scientific-applied research fields, on one hand, and we will follow the teaching programs on “Power engineering,” “Transport management” and “General mechanical engineering,” on the other hand.2.1 Evolution of Engine TechnologiesAs is known from physics, energy conversion follows a natural course, that is, energy of motion of macro- and microbodies (popular as mechanical energy) is converted into heat by mechanisms that are studied by tribology (including dry, semi-dry, viscous, or turbulent friction). No opposite transformation is observed in nature. Heat conversion into energy needed for the operation of machines and mechanisms was an impossible task for primitive people as well as for those living in slave-holding* and feudal†
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