Share
VIDEOS 1 TO 50
Power | Work and energy | Physics | Khan Academy
Power | Work and energy | Physics | Khan Academy
Published: 2013/10/22
Channel: khanacademymedicine
Work, Energy, and Power: Crash Course Physics #9
Work, Energy, and Power: Crash Course Physics #9
Published: 2016/05/26
Channel: CrashCourse
Physics, Power, An Explanation
Physics, Power, An Explanation
Published: 2015/10/27
Channel: Step-by-Step Science
What is power? - Physics
What is power? - Physics
Published: 2014/10/07
Channel: Binogi
Physics - Mechanics: Work, Energy, and Power (1 of 20) Basics
Physics - Mechanics: Work, Energy, and Power (1 of 20) Basics
Published: 2013/09/10
Channel: Michel van Biezen
Energy, Work and Power
Energy, Work and Power
Published: 2011/04/17
Channel: Bozeman Science
Introduction to Power
Introduction to Power
Published: 2016/05/18
Channel: Flipping Physics
Electric power | Circuits | Physics | Khan Academy
Electric power | Circuits | Physics | Khan Academy
Published: 2016/07/29
Channel: Khan Academy Physics
Kinetic Energy, Gravitational & Elastic Potential Energy, Work, Power, Physics - Basic Introduction
Kinetic Energy, Gravitational & Elastic Potential Energy, Work, Power, Physics - Basic Introduction
Published: 2016/09/26
Channel: The Organic Chemistry Tutor
Physics Lecture - 26 - Work and Power
Physics Lecture - 26 - Work and Power
Published: 2012/04/29
Channel: thenewboston
Physics 13.3.1a - Electric Power
Physics 13.3.1a - Electric Power
Published: 2009/09/27
Channel: Derek Owens
GCSE Physics Revision: Power of appliances
GCSE Physics Revision: Power of appliances
Published: 2015/04/12
Channel: Freesciencelessons
A Level Physics - Electrical Power
A Level Physics - Electrical Power
Published: 2015/05/21
Channel: A Level Physics Online
Wind Power Physics
Wind Power Physics
Published: 2015/03/19
Channel: UNL CropWatch: Bioenergy
Electric Current & Circuits Explained, Ohm
Electric Current & Circuits Explained, Ohm's Law, Charge, Power, Physics Problems, Basic Electricity
Published: 2017/02/21
Channel: The Organic Chemistry Tutor
What is Power in Physics?
What is Power in Physics?
Published: 2012/10/31
Channel: mathtutordvd
Don
Don't underestimate the power of physics
Published: 2016/04/16
Channel: Harshit Kasera
High School Physics - Power
High School Physics - Power
Published: 2011/11/28
Channel: Dan Fullerton
IB Physics: Power and Efficiency
IB Physics: Power and Efficiency
Published: 2013/10/25
Channel: Chris Doner
Energy and Power in Electric Circuits.  Joule Heating. | Doc Physics
Energy and Power in Electric Circuits. Joule Heating. | Doc Physics
Published: 2013/01/15
Channel: Doc Schuster
Physics, Power, Calculate the Average Power Output of an Accelerating Car
Physics, Power, Calculate the Average Power Output of an Accelerating Car
Published: 2015/11/15
Channel: Step-by-Step Science
GCSE Physics (9-1) Calculating Power
GCSE Physics (9-1) Calculating Power
Published: 2017/05/30
Channel: Freesciencelessons
The Power of Physics Show - Jan 28th, 2014
The Power of Physics Show - Jan 28th, 2014
Published: 2014/01/24
Channel: powerofphysics
Work Done and Power | GCSE Physics | Doodle Science
Work Done and Power | GCSE Physics | Doodle Science
Published: 2014/01/05
Channel: DoodleScience
NEET I Physics I Work Power Energy I Asgar Khan AGKSir From ETOOSINDIA.COM
NEET I Physics I Work Power Energy I Asgar Khan AGKSir From ETOOSINDIA.COM
Published: 2017/03/20
Channel: Etoos Education
Physics - Mechanics: Work, Energy, and Power (2 of 20) Basic Example
Physics - Mechanics: Work, Energy, and Power (2 of 20) Basic Example
Published: 2013/09/10
Channel: Michel van Biezen
Physics, Power, Calculate Power Output When Running Up Stairs
Physics, Power, Calculate Power Output When Running Up Stairs
Published: 2015/10/27
Channel: Step-by-Step Science
WORK,POWER,ENERGY : ICSE 10th PHYSICS :(in english ) WORK 01 INTRODUCTION : MUST WATCH
WORK,POWER,ENERGY : ICSE 10th PHYSICS :(in english ) WORK 01 INTRODUCTION : MUST WATCH
Published: 2017/07/01
Channel: Physics Wallah
IIT JEE: Physics Online Video lectures-Introduction of Work Power Energy,Force Variable By NKC Sir
IIT JEE: Physics Online Video lectures-Introduction of Work Power Energy,Force Variable By NKC Sir
Published: 2014/11/04
Channel: Eduonlineindia
Physics - Energy - Energy Resources and Power Stations
Physics - Energy - Energy Resources and Power Stations
Published: 2014/01/07
Channel: expertmathstutor
Work Energy Power  for IIT-JEE Physics | IIT Class 11 XI | Physics Video Lecture in Hindi
Work Energy Power for IIT-JEE Physics | IIT Class 11 XI | Physics Video Lecture in Hindi
Published: 2014/07/12
Channel: Dronstudy.com
Physics Lesson - Work, Energy & Power | Iken Edu
Physics Lesson - Work, Energy & Power | Iken Edu
Published: 2015/01/30
Channel: Iken Edu
Introduction to work and energy | Work and energy | Physics | Khan Academy
Introduction to work and energy | Work and energy | Physics | Khan Academy
Published: 2008/02/17
Channel: Khan Academy
Physics - Mechanics: Energy, Work and Power (1 of 5)
Physics - Mechanics: Energy, Work and Power (1 of 5)
Published: 2013/02/03
Channel: Michel van Biezen
How Power Gets to Your Home: Crash Course Physics #35
How Power Gets to Your Home: Crash Course Physics #35
Published: 2016/12/22
Channel: CrashCourse
AP Physics 1: Work and Energy 21: Power, Horsepower, and Power Problems
AP Physics 1: Work and Energy 21: Power, Horsepower, and Power Problems
Published: 2012/08/10
Channel: Yau-Jong Twu
GCSE Physics Revision: Nuclear power
GCSE Physics Revision: Nuclear power
Published: 2015/04/27
Channel: Freesciencelessons
Physics - Mechanics: Work, Energy, and Power (7 of 20) Inclined Plane (Friction)
Physics - Mechanics: Work, Energy, and Power (7 of 20) Inclined Plane (Friction)
Published: 2013/09/11
Channel: Michel van Biezen
Physics Work Energy Power part 1 (Introduction) CBSE class 11
Physics Work Energy Power part 1 (Introduction) CBSE class 11
Published: 2011/08/26
Channel: ExamFear Education
A Level Physics - Mechanical Power
A Level Physics - Mechanical Power
Published: 2015/01/21
Channel: A Level Physics Online
A Level Physics: Mechanics: Energy and Power
A Level Physics: Mechanics: Energy and Power
Published: 2016/08/27
Channel: Burrows Physics
Physics - Mechanics: Work, Energy, and Power (4 of 20) Compressing a Spring
Physics - Mechanics: Work, Energy, and Power (4 of 20) Compressing a Spring
Published: 2013/09/10
Channel: Michel van Biezen
NCEA Science Level 1 Physics: Work and Power
NCEA Science Level 1 Physics: Work and Power
Published: 2012/10/18
Channel: LearnCOACH
Physics- Concept Demonstration "Energy & Power"
Physics- Concept Demonstration "Energy & Power"
Published: 2014/01/15
Channel: Karen Dhillon
Force vs. Power in Physics : Fun With Physics
Force vs. Power in Physics : Fun With Physics
Published: 2014/02/05
Channel: eHowEducation
Power and Efficiency (Introductory Physics)
Power and Efficiency (Introductory Physics)
Published: 2009/09/27
Channel: lasseviren1
Physics - Mechanics: Energy, Work and Power (3 of 5)
Physics - Mechanics: Energy, Work and Power (3 of 5)
Published: 2013/02/03
Channel: Michel van Biezen
Physics Work Energy Power part 12 (Introduction to spring force) CBSE class 11
Physics Work Energy Power part 12 (Introduction to spring force) CBSE class 11
Published: 2011/08/27
Channel: ExamFear Education
Physics Work Energy Power part 4 (Work, Positive, Negative work) CBSE class 11
Physics Work Energy Power part 4 (Work, Positive, Negative work) CBSE class 11
Published: 2011/08/27
Channel: ExamFear Education
High School Physics - Electrical Energy and Power
High School Physics - Electrical Energy and Power
Published: 2011/12/30
Channel: Dan Fullerton
NEXT
GO TO RESULTS [51 .. 100]

WIKIPEDIA ARTICLE

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Power
Common symbols
P
SI unit watt
In SI base units kgm2s−3
SI dimension L^2MT^{-3}
Derivations from
other quantities
  • P = E ∕ t
  • P = Fv
  • P = IU

In physics, power is the rate of doing work, the amount of energy transferred per unit time. Having no direction, it is a scalar quantity. In the SI system, the unit of power is the joule per second (J/s), known as the watt in honour of James Watt, the eighteenth-century developer of the steam engine. Another common and traditional measure is horsepower (comparing to the power of a horse). Being the rate of work, the equation for power can be written:

The integral of power over time defines the work performed. Because this integral depends on the trajectory of the point of application of the force and torque, this calculation of work is said to be path dependent.

As a physical concept, power requires both a change in the physical universe and a specified time in which the change occurs. This is distinct from the concept of work, which is only measured in terms of a net change in the state of the physical universe. The same amount of work is done when carrying a load up a flight of stairs whether the person carrying it walks or runs, but more power is needed for running because the work is done in a shorter amount of time.

The output power of an electric motor is the product of the torque that the motor generates and the angular velocity of its output shaft. The power involved in moving a vehicle is the product of the traction force of the wheels and the velocity of the vehicle. The rate at which a light bulb converts electrical energy into light and heat is measured in watts—the higher the wattage, the more power, or equivalently the more electrical energy is used per unit time.[1][2]

Units[edit]

The dimension of power is energy divided by time. The SI unit of power is the watt (W), which is equal to one joule per second. Other units of power include ergs per second (erg/s), horsepower (hp), metric horsepower (Pferdestärke (PS) or cheval vapeur (CV)), and foot-pounds per minute. One horsepower is equivalent to 33,000 foot-pounds per minute, or the power required to lift 550 pounds by one foot in one second, and is equivalent to about 746 watts. Other units include dBm, a relative logarithmic measure with 1 milliwatt as reference; food calories per hour (often referred to as kilocalories per hour); Btu per hour (Btu/h); and tons of refrigeration (12,000 Btu/h).

Equations for power[edit]

Power, as a function of time, is the rate at which work is done, so can be expressed by this equation:

Because work is a force applied over a distance, this can be rewritten as:

And with distance per unit time being a velocity, power can likewise be understood as:

Knowing from Newton's 2nd Law that force is mass times acceleration, the expression for power can also be written as:

Power will change over time as velocity changes due to acceleration. Knowing that acceleration is the time rate of change of velocity, this can then be written:

Comparing with the equation for kinetic energy:

It can be seen from the previous equation that power is mass times a velocity term times another velocity term divided by time. This shows how power is an amount of energy consumed per unit time.

Average power[edit]

As a simple example, burning a kilogram of coal releases much more energy than does detonating a kilogram of TNT,[3] but because the TNT reaction releases energy much more quickly, it delivers far more power than the coal. If ΔW is the amount of work performed during a period of time of duration Δt, the average power Pavg over that period is given by the formula

It is the average amount of work done or energy converted per unit of time. The average power is often simply called "power" when the context makes it clear.

The instantaneous power is then the limiting value of the average power as the time interval Δt approaches zero.

In the case of constant power P, the amount of work performed during a period of duration T is given by:

In the context of energy conversion, it is more customary to use the symbol E rather than W.

Mechanical power[edit]

One metric horsepower is needed to lift 75 kilograms by 1 meter in 1 second.

Power in mechanical systems is the combination of forces and movement. In particular, power is the product of a force on an object and the object's velocity, or the product of a torque on a shaft and the shaft's angular velocity.

Mechanical power is also described as the time derivative of work. In mechanics, the work done by a force F on an object that travels along a curve C is given by the line integral:

where x defines the path C and v is the velocity along this path.

If the force F is derivable from a potential (conservative), then applying the gradient theorem (and remembering that force is the negative of the gradient of the potential energy) yields:

where A and B are the beginning and end of the path along which the work was done.

The power at any point along the curve C is the time derivative

In one dimension, this can be simplified to:

In rotational systems, power is the product of the torque τ and angular velocity ω,

where ω measured in radians per second. The represents scalar product.

In fluid power systems such as hydraulic actuators, power is given by

where p is pressure in pascals, or N/m2 and Q is volumetric flow rate in m3/s in SI units.

Mechanical advantage[edit]

If a mechanical system has no losses, then the input power must equal the output power. This provides a simple formula for the mechanical advantage of the system.

Let the input power to a device be a force FA acting on a point that moves with velocity vA and the output power be a force FB acts on a point that moves with velocity vB. If there are no losses in the system, then

and the mechanical advantage of the system (output force per input force) is given by

The similar relationship is obtained for rotating systems, where TA and ωA are the torque and angular velocity of the input and TB and ωB are the torque and angular velocity of the output. If there are no losses in the system, then

which yields the mechanical advantage

These relations are important because they define the maximum performance of a device in terms of velocity ratios determined by its physical dimensions. See for example gear ratios.

Electrical power[edit]

Ansel Adams photograph of electrical wires of the Boulder Dam Power Units
Ansel Adams photograph of electrical wires of the Boulder Dam Power Units, 1941–1942

The instantaneous electrical power P delivered to a component is given by

where

P(t) is the instantaneous power, measured in watts (joules per second)
V(t) is the potential difference (or voltage drop) across the component, measured in volts
I(t) is the current through it, measured in amperes

If the component is a resistor with time-invariant voltage to current ratio, then:

where

is the resistance, measured in ohms.

Peak power and duty cycle[edit]

In a train of identical pulses, the instantaneous power is a periodic function of time. The ratio of the pulse duration to the period is equal to the ratio of the average power to the peak power. It is also called the duty cycle (see text for definitions).

In the case of a periodic signal of period , like a train of identical pulses, the instantaneous power is also a periodic function of period . The peak power is simply defined by:

.

The peak power is not always readily measurable, however, and the measurement of the average power is more commonly performed by an instrument. If one defines the energy per pulse as:

then the average power is:

.

One may define the pulse length such that so that the ratios

are equal. These ratios are called the duty cycle of the pulse train.

Radiant power[edit]

Power is related to intensity at a distance r, the power emitted by a source can be written as:[citation needed]

See also[edit]

References[edit]

  1. ^ Halliday and Resnick (1974). "6. Power". Fundamentals of Physics. 
  2. ^ Chapter 13, § 3, pp 13-2,3 The Feynman Lectures on Physics Volume I, 1963
  3. ^ Burning coal produces around 15-30 megajoules per kilogram, while detonating TNT produces about 4.7 megajoules per kilogram. For the coal value, see Fisher, Juliya (2003). "Energy Density of Coal". The Physics Factbook. Retrieved 30 May 2011.  For the TNT value, see the article TNT equivalent. Neither value includes the weight of oxygen from the air used during combustion.

Disclaimer

None of the audio/visual content is hosted on this site. All media is embedded from other sites such as GoogleVideo, Wikipedia, YouTube etc. Therefore, this site has no control over the copyright issues of the streaming media.

All issues concerning copyright violations should be aimed at the sites hosting the material. This site does not host any of the streaming media and the owner has not uploaded any of the material to the video hosting servers. Anyone can find the same content on Google Video or YouTube by themselves.

The owner of this site cannot know which documentaries are in public domain, which has been uploaded to e.g. YouTube by the owner and which has been uploaded without permission. The copyright owner must contact the source if he wants his material off the Internet completely.

Powered by YouTube
Wikipedia content is licensed under the GFDL and (CC) license