We explain what power is in physics, the types that exist and various examples. Also, the formulas to calculate it.
What is power in physics?
In physics, power (represented by the symbol Q) is a given amount of work done in some way in a given unit of time. I mean, is the amount of work per unit of time that some object or system produces.
The power It is measured in watts (W) a unit that pays tribute to the Scottish inventor James Watt and is equivalent to one joule (J) of work done per second (s), that is:
W = J/s
In the Anglo-Saxon system of measurements, this unit is replaced by horsepower (hp).
The ability to understand and measure power accurately was a determining factor in the development of the first steam engines, the device on which the Industrial Revolution was sustained. Nowadays, however, it is usually associated with electricity and other types of modern energy resources, since it is also can designate the amount of energy transmitted.
See also: Mechanics in physics
Power Types
There are the following types of power:
- Mechanical power That which is derived from the application of a force on a rigid solid, or a deformable solid.
- Electrical power Instead of work, it refers to the amount of energy transmitted per unit of time in a system or circuit.
- Heating power It refers to the amount of heat that a body releases to the environment per unit of time.
- Sound power It is understood as the amount of energy that a sound wave transports per unit of time across a given surface.
Power formulas
The power is calculated, in general terms, according to the following formula:
P = ΔE/ Δt
ΔE represents the change in energy or the change in work.
Δt represents the time measured in seconds.
However, each type of power is expressed by its own formulation, for example:
- Mechanical power. P
- Electrical power. P
- Heating power P = E/t, where E is the heat energy provided, measured in joules (J). Note how this is indifferent to degrees of heat.
- Sound power QYes = ʃYoyes dS, where Yoyes is the sound intensity and dS is the element reached by the wave.
Examples of power
- Power to move a mass
We want to lift 100 kg of construction materials to the seventh floor of a building under construction, that is, about 20 meters from the ground. We want to do it using a crane and in 4 seconds of time, so we must find out the necessary power of the crane.
To use the formula P = w/t, we must calculate the work done by the crane first.
For this we use the formula W = F. d. cos a = 100 x 9.8 x 20 x 1 = 19,600 N. Then: P = 19,600 N / 4 s, that is, the power of the crane will have to be 4900 W.
- Power dissipated by a resistance
We must calculate the amount of power dissipated by an electrical resistance of 10 ohms, when we pass through it with a current of 10 amperes. In this case we apply the formula P = R x I2as follows: P = 10 x 102which results in a dissipated power of 1000 watts.
Continue with: Acceleration
References
- “Power (physics)” on Wikipedia.
- “What is power?” at Khan Academy.
- “Definition of power” in Fisicalab.
- “Power” in The Encyclopaedia Britannica.
