notes of work and energy, power 9 class
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Energy is a word which tends to be used a lot in everyday life. Though it is often used quite loosely, it does have a very specific physical meaning.
Energy is a measurement of the ability of something to do work. It is not a material substance. Energy can be stored and measured in many forms.
Although we often hear people talking about energy consumption, energy is never really destroyed. It is just transferred from one form to another, doing work in the process. Some forms of energy are less useful to us than others—for example, low level heat energy. It is better to talk about the consumption or extraction of energy resources, for example coal, oil, or wind, than consumption of energy itself.
A speeding bullet has a measurable amount of energy associated with it; this is known as kinetic energy. The bullet gained this energy because work was done on it by a charge of gunpowder which lost some chemical potential energy in the process.
A hot cup of coffee has a measurable amount of thermal energy which it acquired via work done by a microwave oven, which in turn took electrical energy from the electrical grid.
In practice, whenever work is done to move energy from one form to another, there is always some loss to other forms of energy such as heat and sound. For example, a traditional light bulb is only about 3% efficient at converting electrical energy to visible light, while a human being is about 25% efficient at converting chemical energy from food into work.
How do we measure energy and work?
The standard unit used to measure energy and work done in physics is the joule, which has the symbol J. In mechanics, 1 joule is the energy transferred when a force of 1 Newton is applied to an object and moves it through a distance of 1 meter.
Another unit of energy you may have come across is the Calorie. The amount of energy in an item of food is often written in Calories on the back of the packet. A typical 60 gram chocolate bar for example contains about 280 Calories of energy. One Calorie is the amount of energy required to raise 1 kg of water by 1^{\circ}∘degreeCelsius.
Energy is a measurement of the ability of something to do work. It is not a material substance. Energy can be stored and measured in many forms.
Although we often hear people talking about energy consumption, energy is never really destroyed. It is just transferred from one form to another, doing work in the process. Some forms of energy are less useful to us than others—for example, low level heat energy. It is better to talk about the consumption or extraction of energy resources, for example coal, oil, or wind, than consumption of energy itself.
A speeding bullet has a measurable amount of energy associated with it; this is known as kinetic energy. The bullet gained this energy because work was done on it by a charge of gunpowder which lost some chemical potential energy in the process.
A hot cup of coffee has a measurable amount of thermal energy which it acquired via work done by a microwave oven, which in turn took electrical energy from the electrical grid.
In practice, whenever work is done to move energy from one form to another, there is always some loss to other forms of energy such as heat and sound. For example, a traditional light bulb is only about 3% efficient at converting electrical energy to visible light, while a human being is about 25% efficient at converting chemical energy from food into work.
How do we measure energy and work?
The standard unit used to measure energy and work done in physics is the joule, which has the symbol J. In mechanics, 1 joule is the energy transferred when a force of 1 Newton is applied to an object and moves it through a distance of 1 meter.
Another unit of energy you may have come across is the Calorie. The amount of energy in an item of food is often written in Calories on the back of the packet. A typical 60 gram chocolate bar for example contains about 280 Calories of energy. One Calorie is the amount of energy required to raise 1 kg of water by 1^{\circ}∘degreeCelsius.
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Work is said to be done when force applied on body moves the body through some distance in the direction of force .Its S.I unit is newton.
W=F×S
Energy can be defined as the capacity to do work.
Power is the rate of doing work in the unit time .In S.I it is measured in watt
P=W/T .
W=F×S
Energy can be defined as the capacity to do work.
Power is the rate of doing work in the unit time .In S.I it is measured in watt
P=W/T .
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