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Definition of mass, force, weight, electrical energy, efficiency | difference between mass and weight

1. Mass

It is the quantity of matter possessed by a body. The SI unit of mass is the kilogram (kg). The mass of a body is a constant quantity and is independent of the place and position of the body. Thus the mass of a body is the same whether it is on the earth’s surface, the moon’s surface, on the top of a mountain, or down a deep well.

2. Force

It is the product of mass (kg) and acceleration (m/s2). The unit of force is newton (N); being the force required to accelerate a mass of 1 kg through an acceleration of 1 m/s2.
F = m a newtons
where m = mass of the body in kg
a = acceleration in m/s2

3. Weight

The force with which a body is attracted towards the center of the earth is called the weight of the body. Now, force = mass x acceleration. If it is the mass of a body in kg and g is the acceleration due to gravity in m/s2, then,
Weight, W = m g newtons
As the value of g varies from place to place on the earth’s surface, therefore, the weight of the body varies accordingly. However, for practical purposes, we take g = 9.81 m/s2 so that the weight of the body = 9.81 m newtons. Thus if a mass of 1 kg rests on a table, the downward force on the table i.e., the weight of the body is W = 9.81 x 1 = 9.81 newtons.

4. Electrical Energy

The SI unit of electrical work done or electrical energy expended in a circuit is also joule —exactly the same as for mechanical energy. It is defined as under :
One joule of energy is expended electrically when one coulomb is moved through a p.d. of 1volt.

5. Efficiency

The efficiency of a device or of a circuit is the ratio of useful output to the. input i.e.
Efficiency, η = useful output/input = Wo/Wi

The law of conservation of energy states that “energy cannot be created or destroyed but can is converted from one form to another-. Some of the energy in electric circuits may be converted into a form that is not useful. For example, consider an electric motor shown in Fig. 1. The purpose of the motor is to convert electric energy into mechanical energy. It does this, but it also converts a part of input energy into heat. The heat produced is not useful. Therefore, the useful output energy is less than the input energy. In other words, the efficiency of the motor is less than 100%.
Some electrical devices are nearly 100% efficient. An electric heater is an example. in a heater, practically all the input electric energy is converted into heat energy. In this case, the heat is useful to output.

fig.1 efficiency

difference between mass and weight

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Aanchal Gupta

Welcome to my website! I'm Aanchal Gupta, an expert in Electrical Technology, and I'm excited to share my knowledge and insights with you. With a strong educational background and practical experience, I aim to provide valuable information and solutions related to the field of electrical engineering. I hold a Bachelor of Engineering (BE) degree in Electrical Engineering, which has equipped me with a solid foundation in the principles and applications of electrical technology. Throughout my academic journey, I focused on developing a deep understanding of various electrical systems, circuits, and power distribution networks.

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