Work, Energy and Power

Comprehensive vocabulary flashcards covering concepts, definitions, formulas, and units of work, energy, and power.

Work (Physics Definition)

The measure of exertion where work is said to be done only when a force applied on a body makes the body undergo a displacement.

Work Expression (Scalar Product)

The dot product of force and displacement vectors, written as W = \t{F} \cdot \t{S} = F \times S \times \cos(\theta), where $F$ is the magnitude of force, $S$ is displacement, and $\theta$ is the angle between them.

Positive Work

Work done when the displacement of a body is in the exact direction of the applied force ($\theta = 0^\circ$), resulting in $W = F \times S$.

Conditions for Zero Work

The two situations where work done by a force is zero: when there is no displacement ($S = 0$), or when displacement is normal to the direction of force ($\theta = 90^\circ$).

Zero Work in Circular Motion

The condition where centripetal force acts towards the center while displacement is along the tangent, making $\theta = 90^\circ$ and work done $W = 0$.

Negative Work

Work done when the displacement of a body is in a direction opposite to the applied force ($\theta = 180^\circ$), resulting in $W = -F \times S$.

Force-Displacement Graph

A plot of force $F$ on the Y-axis against displacement $S$ on the X-axis, where the area enclosed between the curve and the X-axis represents the total work done.

Work Done by Gravity

The work given by $W = m \times g \times h$, when a body of mass $m$ is moved vertically through height $h$, independent of the path taken.

Joule ($\text{J}$)

The S.I. unit of work, defined as the work done when a force of $1\,\text{N}$ displaces a body through a distance of $1\,\text{m}$ in its own direction ($1\,\text{J} = 1\,\text{N} \times 1\,\text{m}$).

Erg

The C.G.S. unit of work, defined as the work done when a force of $1\,\text{dyne}$ displaces a body through a distance of $1\,\text{cm}$ in its own direction ($1\,\text{erg} = 1\,\text{dyne} \times 1\,\text{cm}$).

Power

A scalar quantity defined as the rate of doing work or the amount of work done by a source in one second ($P = \frac{W}{t}$).

Power in terms of Speed

The product of force and average speed, expressed as $P = F \times v$.

Watt ($\text{W}$)

The S.I. unit of power, representing a rate of work of $1\,\text{joule}$ done in $1\,\text{second}$ ($1\,\text{W} = 1\,\text{J\,s}^{-1}$).

Horse Power ($\text{HP}$)

A unit of power largely used in mechanical engineering, equal to $746\,\text{W}$ or $0.746\,\text{kW}$.

Energy

A scalar quantity defined as the capacity of a body to do work, measured by the total amount of work the body can perform.

Watt Hour ($\text{Wh}$)

A unit of work or energy equivalent to the energy spent by a source of power $1\,\text{W}$ operating for $1\,\text{h}$, equal to $3600\,\text{J}$ or $3.6\,\text{kJ}$.

Kilowatt Hour ($\text{kWh}$)

A unit of work or energy equivalent to the energy spent by a source of power $1\,\text{kW}$ operating for $1\,\text{h}$, equal to $3.6 \times 10^6\,\text{J}$ or $3.6\,\text{MJ}$.

Calorie

A unit of heat energy defined as the heat required to raise the temperature of $1\,\text{g}$ of water from $14.5^\circ\text{C}$ to $15.5^\circ\text{C}$, equal to $4.18\,\text{J}$.

Electron Volt ($\text{eV}$)

A unit of energy for atomic particles, defined as the energy gained by an electron when accelerated through a potential difference of $1\,\text{volt}$, equal to $1.6 \times 10^{-19}\,\text{J}$.

Work

A scalar quantity defined as the product of the force and the displacement of the point of application of the force in the direction of the force, represented mathematically as $W = F S \cos(\theta)$.

Positive Work

Work done when the displacement of a body is in the exact direction of the applied force ($\theta = 0^\circ$), yielding $W = F \times S$ (e.g., free fall of a body under gravity).

Zero Work

The condition where no work is done because there is no displacement ($S = 0$) or because the displacement is normal to the direction of force ($\theta = 90^\circ$), such as centripetal force acting in circular motion.

Negative Work

Work done when the displacement is in a direction opposite to the applied force ($\theta = 180^\circ$), giving $W = -F \times S$ (e.g., friction opposing motion or work done by gravity on an upward thrown ball).

Force-Displacement Graph Area

The area enclosed between the plot of force vs. displacement and the displacement axis ($X\text{-axis}$), which quantitatively equals the work done by the force.

Work Done by Gravity

The work performed when a body of mass $m$ moves through a vertical height $h$, expressed as $W = m g h$, which is independent of the path taken (whether via stairs, inclined plane, slope, or elevator).

Joule

The S.I. unit of work and energy (abbreviated as $\text{J}$), defined as the work done when a force of $1\,\text{newton}$ displaces a body through a distance of $1\,\text{metre}$ in its own direction.

Erg

The C.G.S. unit of work and energy, defined as the work done when a force of $1\,\text{dyne}$ displaces a body through a distance of $1\,\text{cm}$ in its own direction ($1\,\text{joule} = 10^7\,\text{erg}$).

Power

The scalar quantity defined as the rate of doing work, or the amount of work done per unit time ($P = \frac{W}{t}$), which can also be calculated as force times average speed ($P = F \times v$).

Watt

The S.I. unit of power (abbreviated as $\text{W}$), defined as the power spent when $1\,\text{joule}$ of work is done in $1\,\text{second}$ ($1\,\text{W} = 1\,\text{J\,s}^{-1} = 10^7\,\text{erg\,s}^{-1}$).

Horse Power

A unit of power largely used in mechanical engineering, related to the S.I. unit watt by $1\,\text{H.P.} = 746\,\text{W} = 0.746\,\text{kW}$.

Energy

The capacity of a body to do work, which is a scalar quantity measured by the total amount of work the body can perform.

Watt Hour

A unit of work or energy (abbreviated as $\text{Wh}$) spent by a source of power $1\,\text{W}$ in $1\,\text{h}$, equivalent to $3600\,\text{J}$ or $3.6\,\text{kJ}$.

Kilowatt Hour

A unit of work or energy (abbreviated as $\text{kWh}$) spent by a source of power $1\,\text{kW}$ in $1\,\text{h}$, equivalent to $3.6 \times 10^6\,\text{J}$ or $3.6\,\text{MJ}$.

Calorie

A unit of heat energy required to raise the temperature of $1\,\text{g}$ of water from $14.5^\circ\text{C}$ to $15.5^\circ\text{C}$, where $1\,\text{calorie} = 4.18\,\text{J}$ ($1\,\text{J} = 0.24\,\text{calorie}$).

Kilocalorie

A unit of heat energy equal to $1000\,\text{calories}$ or $4180\,\text{J}$.

Electron Volt

A unit of energy used for atomic particles (abbreviated as $\text{eV}$), defined as the energy gained by an electron accelerated through a potential difference of $1\,\text{volt}$, equal to $1.6 \times 10^{-19}\,\text{J}$.

Principle of Conservation of Energy

The law stating that total mechanical energy remains constant ($U + K = \text{constant}$) for a freely falling body or conservative system, where energy converts between forms without being created or destroyed.