power in physics



We explain what power is in physics, the types that exist and various examples. Also, the formulas to calculate it.

Power is the amount of work done in a given time.

What is power in physics?

In physics, the power (represented by the symbol P) is a specified amount of job effected in some way in a unit of weather determined. In other words, it is the amount of work per unit of time that some object or system produces.

Power is measured in watts (W), a unit that pays homage to Scottish inventor James Watt and equates to one joule (J) of work done by second (s), that is:

W = J / s

In the Anglo-Saxon system of measurements, this unit is replaced by the horses of force (hp).

The ability to understand and measure power accurately was a determining factor in the development of the first steam engines, a device on which the Industrial Revolution. Nowadays, on the other hand, it is usually associated with electricity and another type of energetic resources modern, as you can also designate the amount of Energy transmitted.

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.
  • Electric power. Instead of work, it refers to the amount of energy transmitted per unit time in a system or circuit.
  • Heating power. Refers to the amount of heat that a body frees 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 through a given surface.

Power formulas

The power of a machinery tells us if it can do a job.

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 potency is expressed through its own formulation, for example:

  • Mechanical power P (t) = F.v, although if there is a rotation of the solid and the applied forces alter its angular velocity, we will use P (t) = F.v + M.ω instead. F and M will be the resultant force and the resultant moment, respectively; while V and ω will be the velocity of the point over which the resultant was calculated, and the angular velocity of the body.
  • Electric power. P (t) = I (t). V (t), where I is the flowing current, measured in amperes, and V is the potential difference (the drop in voltage) measured in volts. In the case of a endurance Instead of a conductor of electricity, the formula to be used will be P = I2R = V2 / R, where R is the resistance of the material, measured in ohms.
  • Heating power. P = E / t, where E is the provided heat energy, measured in joules (J). Note how this is indifferent to degrees of heat.
  • Sound power. PS = ʃIs dS, where Is is the sound intensity and dS the element reached by the wave.

Power examples

  • Power to move a mass

We want to raise 100 kg of construction materials to the seventh floor of a building under construction, that is, about 20 meters from the I usually. We want to do it using a crane and in 4 seconds of time, so we must find out the necessary power of the same.

To use the formula P = w / t, we must calculate the work done by the crane first.

For that 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 must be 4900 W.

  • Power dissipating a resistor

We must calculate the amount of power that an electrical resistance of 10 ohms dissipates, when we cross it with a current 10 amps. In this case we apply the formula P = R x I2, as follows: P = 10 x 102, which results in a dissipated power of 1000 watts.

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