### BBC Bitesize - GCSE Physics (Single Science) - Power and efficiency - Edexcel - Revision 1

Power is the capacity of energy, which is being used. In more simple terms, power is defined as the rate of doing work. Power finds it use in. A simple way of understanding the relationship between work, power and energy involves turning a bolt inside a tight nut using a wrench. Work is defined as. Although we often use the words "energy" and "power" synonymously, they are not the same. View this interactive to discover what sets energy.

And how is energy lost from our homes?

### What is the relationship between power and energy? - Physics Stack Exchange

Energy escapes through the walls, windows, roof and floor through conduction — energy moving from the warm internal space to the cold exterior space. Even drying clothes indoors uses up energy. The evaporation of 1 litre of water from damp washing requires the same energy as boiling a 1 litre kettle dry.

It just happens at a much lower temperature, and so it takes longer than evaporating water in a kettle.

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That last example helps explain the relationship between Power and Energy. Power is the rate at which energy is used. It is measured in Kilowatt-hours per hour.

So in that respect we write Energy as Kilowatt-hours, or kWh. Put another way, Energy is the distance you travelled in a car milesand Power is the speed you went at to get there miles per hour. So, we have a 3kW electric kettle. The 3kW is its power.

A 6kW kettle is faster. If it takes a 3kW kettle just 60 seconds to boil a litre of water, it will take a 6kW kettle thirty seconds, because the 6kW has a higher Power. How does power relate to my energy bills? You are an average Englishman and therefore you drink 10 cups of tea a day.

## The relationship between Power and Energy – and what it has to do with your home

You boil the kettle ten times a day. The calculation to work out how much energy you use making tea is simple: This is our Energy. Power is related to how fast a job is done. Two identical jobs or tasks can be done at different rates - one slowly or and one rapidly.

The work is the same in each case since they are identical jobs but the power is different. The equation for power shows the importance of time: Special attention should be taken so as not to confuse the unit Watt, abbreviated W, with the quantity work, also abbreviated by the letter W. Combining the equations for power and work can lead to a second equation for power.

A few of the problems in this set of problems will utilize this derived equation for power. Mechanical, Kinetic and Potential Energies There are two forms of mechanical energy - potential energy and kinetic energy.

Potential energy is the stored energy of position. In this set of problems, we will be most concerned with the stored energy due to the vertical position of an object within Earth's gravitational field. Kinetic energy is defined as the energy possessed by an object due to its motion. An object must be moving to possess kinetic energy. The amount of kinetic energy KE possessed by a moving object is dependent upon mass and speed.

The total mechanical energy possessed by an object is the sum of its kinetic and potential energies. Work-Energy Connection There is a relationship between work and total mechanical energy.

The final amount of total mechanical energy TMEf possessed by the system is equivalent to the initial amount of energy TMEi plus the work done by these non-conservative forces Wnc.

The mechanical energy possessed by a system is the sum of the kinetic energy and the potential energy. Positive work is done on a system when the force doing the work acts in the direction of the motion of the object.

Negative work is done when the force doing the work opposes the motion of the object. When a positive value for work is substituted into the work-energy equation above, the final amount of energy will be greater than the initial amount of energy; the system is said to have gained mechanical energy.

When a negative value for work is substituted into the work-energy equation above, the final amount of energy will be less than the initial amount of energy; the system is said to have lost mechanical energy. There are occasions in which the only forces doing work are conservative forces sometimes referred to as internal forces. Typically, such conservative forces include gravitational forces, elastic or spring forces, electrical forces and magnetic forces.

## Mechanics: Work, Energy and Power

When the only forces doing work are conservative forces, then the Wnc term in the equation above is zero. In such instances, the system is said to have conserved its mechanical energy. The proper approach to work-energy problem involves carefully reading the problem description and substituting values from it into the work-energy equation listed above. Inferences about certain terms will have to be made based on a conceptual understanding of kinetic and potential energy.