7.7 Power

60 J of energy is used by a 60-W light bulb.
A large amount of work or energy can be developed in a short time.
When a car is fast, it consumes a lot of fuel in a short time and does a lot of work.

The woman converts the chemical energy from food to energy when she runs upstairs.

Where is the vertical height of the stairs when we take both and as initially zero at the bottom of the stairs?

The woman does 1764 J of work to move up the stairs compared with 120 J to increase her energy output, so most of her power output is required to climb rather than accelerate.

People can quickly convert available blood sugar and oxygen into work output by using their leg muscles.

The aerobic stage of exercise is when the power output decreases and the person begins to breathe quickly to get more oxygen.
The power output of the woman would be less if she climbed the stairs slowly.

Measure the time it takes you to climb a flight of stairs to determine your power rating.

The rate at which fossil fuels are consumed is greater than the rate at which they are stored, so it is inevitable that they will be exhausted.
Power means that energy is transferred.
It is not possible to change one form completely into another.
A 60-W bulb converts only 5 W of electrical power to light, with 55 W dissipating into thermal energy.
The typical electric power plant converts 35 to 40% of its fuel into electricity.
A huge amount of thermal energy must be dispersed as quickly as possible.
A coal-fired power plant can produce 1000 megawatts; 1 megawatt is of electric power.
The power plant creates heat transfer from the chemical energy it consumes to the surroundings at a rate of 1500 MW.

Tremendous amounts of electric power are generated by coal-fired power plants such as this one in China, but an even larger amount of power goes into heat transfer to the surroundings.

The cooling towers here need to transfer heat as quickly as possible.
The transfer of heat is not unique to coal plants, but is an unavoidable consequence of generating electric power from any fuel.

It is easy to estimate the cost of energy for an appliance if it is known how much power it uses.
The higher the power consumption rate, the higher the cost of the appliance.
Where is the energy supplied by the electricity company?

The unit is convenient because the electrical power consumption for hours at a time is typical.

With the price increasing, the motivation to save energy has become more compelling.

You can estimate costs for yourself if you know that energy is the product of power and time.
The power or time must be reduced.
Limit the use of high-power devices that operate for long periods of time is the most cost-effective way to do it.
This would not include devices that are high in power because they are only on a few minutes a day.
It wouldn't include electric clocks because they are very low power devices.
Sometimes it is possible to use devices that consume less power to accomplish the same task.
One example is the compact fluorescent light bulb, which uses four times more power to produce the same amount of light.

The likelihood of a link between global warming and fossil fuel use has made reduction in energy use as well as a shift to non-fossil fuels of the utmost importance.
Even though energy in an isolated system is a conserved quantity, the final result is waste heat transfer to the environment, which is no longer useful for doing work.
The potential for energy to produce useful work has been degraded by the energy transformation.

Chemical energy in food can be converted into work, thermal energy, and/or stored as chemical energy in fat.
If we eat more than we need to, the rest goes into our body fat.

The majority of calories burned in a day go into these basic functions.
The BMR is a function of age, gender, total body weight, and amount of muscle mass.
Athletes have a higher BMR because of this last factor.

Useful work requires force to be exert through a distance on the outside world, and so it excludes internal work, such as that done by the heart when pumping blood.

Useful work can be accomplished by climbing stairs or running a full run because the outside world exerts force on them.
The body exerts nonconservative forces so that they can change the mechanical energy of the system.
A baseball player throwing a ball increases the ball's potential energy.

If a person needs more energy than they consume, the body must use the chemical energy stored in fat.

A person who normally requires 12,000 kJ of food energy per day will gain weight if he consumes 13,000 kJ per day.

If this person uses more energy than he or she consumes, the person's body will get the needed energy by burning body fat.

The rate at which food energy is converted to another form is what the knowledge of oxygen and carbon dioxide levels indicates.
It is possible to determine the level of athletic conditioning as well as some medical problems.