Convert MBH to kilowatt [kW] • Power Converter • Common Unit Converters • Compact Calculator • Online Unit Converters (2024)

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Overview

Power in physics is the ratio of work to time. Here, work refers to the amount of force F needed to move a body along the distance s. It could also be defined as the speed of energy transfer. In other words, power is an indicator of the machine’s capacity to do work.

Units

Power is measured in joules per second, or watts. Along with watts, horsepower as a unit is also used. Until the invention of engines, power was not measured formally, and there were no units associated with it. After the steam engine was invented, James Watt, an inventor and engineer, worked on improving it and on making it more efficient. Power is one indicator of efficiency — if a given engine is modified and its power output increases, so does its efficiency. To show the efficiency of the improved engine Watt suggested horsepower as a unit of power. Until the invention of engines, humans relied mainly on human and animal manual labor, so it was natural for Watt to compare the power output of the new steam engine with the power of horses, especially because not every mine where he marketed his steam engine used technology; some used only horses. Thus, having a standardized measure was useful for comparing the power output between different engines and horses. This measure was later used for other machines such as automobiles. Watt measured this unit of power by observing and evaluating the work of draft horses in a mill. One horsepower is equivalent to 746 watts. It is now believed that horses are not capable of working at this capacity for a long period of time, but the unit stays unchanged. Even though watts as a unit have existed nearly as long as horsepower, the latter is more commonly used in the automobile industry.

Power of Household Appliances

Household appliances generally have their power indicated on them. Light fixtures sometimes allow only light bulbs of or below a certain power, for example, 60 watts. This is because light bulbs with greater power may damage the lamp or the fixture due to the heat they produce. In household lighting, this problem may be solved by using lamps that are not incandescent, as those generally consume considerably less power for the same brightness output.

Most manufacturers are working on improving the efficiency of appliances, as well as light bulbs. The brightness or luminosity of a light bulb depends on power and the type of bulb. It is measured in lumens. Below is a comparison of the power of different light sources for home use, with luminous power information.

• 450 lumens:
• Incandescent: 40 watts
• Compact fluorescent: 9–13 watts
• LED: 4–9 watts
• 800 lumens:



12 W and 7 W fluorescent lamps

• Incandescent: 60 watts
• Compact fluorescent: 13–15 watts
• LED: 10–15 watts
• 1600 lumens
• Incandescent: 100 watts
• Compact fluorescent: 23–30 watts
• LED: 16–20 watts

It is evident from the comparison above that the LEDs require less power, thus they are more efficient in operation. A unit price for an LED light is still high compared to incandescent lights, but over the long-term use, it is cost-efficient. Some countries implemented or are planning to implement a ban on incandescent lights because of their low energy efficiency.

The power of household appliances differs by the maker and the model and they have different power while performing different types of work, but here are some examples of average and approximate values.



5050 LED strip. One LED consumes approximately 200 mW

• Residential split system air conditioners: 20–40 kilowatts
• Window air conditioners: 1–2 kilowatts
• Ovens: 2.1–3.6 kilowatts
• Washers and dryers: 2–3.5 kilowatts
• Dishwashers: 1.8–2.3 kilowatts
• Electric pots: 1–2 kilowatts
• Microwave ovens: 0.65–1.2 kilowatts
• Refrigerators: 0.5–1 kilowatt
• Toasters: 0.7–0.9 kilowatts



Power in Sports

Machines are not the only objects that can be evaluated through power. Work produced by animals and humans can be measured using power. For example, the power of an athlete throwing a basketball can be calculated by finding the force, with which she propels the ball for a given distance and the time during which she completes this work. Some websites help athletes calculate the work performed and the power output for different types of physical exercises, based on the weight of the athlete and of the equipment used, the distance traveled, estimated using the athlete’s height for exercises like weight lifting, and the exercise duration. For example, this calculator shows that a person 170 cm tall and weighing 70 kg will produce a power output of 39.5 watts by doing 50 push-ups for 10 minutes. Some athletes use special devices for these calculations, record their performance with respect to power output, and then analyze it to determine the effectiveness of their workout program.

Dynamometers

Power can be measured by a special device, a dynamometer. Dynamometers can also measure torque and force. They can have a range of applications, from engineering to the medical field. For example, dynamometers can help measure and evaluate the power output of engines. There are two types of dynamometers, the engine, and the chassis type. Engine dynamometers can only work with engines, taken out of the vehicle or machine, but they are more accurate. Chassis ones can be used more easily, but are less accurate and more expensive.



A chassis dynamometer can measure torque and power delivered by the power train of a vehicle

Dynamometers can also be used to calculate the strength of people for sports or medical reasons. They are usually the isokinetic type. An isokinetic dynamometer consists of an exercise machine with sensors, connected to a computer. It measures the strength of different muscle groups. Along with the overall measurements for the body, they can measure the power output for specific muscle groups. They can be programmed to provide warnings when a given power threshold is exceeded. This is useful for people with injuries undergoing rehabilitation, or for those who want to carefully monitor their exercise routines.

According to some theories of exercise, the biggest performance improvement happens at a certain range of stimuli for a given individual. When the exercise is too easy, there is no improvement, and when the exercise is too difficult, the athlete may have poor performance due to overstraining. For exercises that depend on the environment, such as cycling and swimming, it is difficult to measure the stimulus, because one has to consider various environmental aspects such as the effect of wind or the conditions of the ground or water on the strain, produced by exercise. Power is one of the easiest ways to measure this stimulus by tracking the response of the athlete to the stimulus with a dynamometer; therefore it is a useful concept in exercise.

References

This article was written by Kateryna Yuri

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