Work, Energy and Power - Physics Vocabulary

Vocabulary practice flashcards defining key physics terms, equations, units, and equilibrium states from Chapter 7: Work, Energy and Power.

Work Done by Constant Force

The scalar (dot) product of the force vector $\vec{F}$ and displacement vector $\vec{S}$, evaluated as W = \bvec{F} \bdot \bvec{S} = F S \cos(\theta), where $F$ is force magnitude, $S$ is displacement magnitude, and $\theta$ is the angle between them.

Joule ($J$)

The SI unit of work and energy, defined as $1\,J = 1\,N \times 1\,m$.

Erg

The CGS unit of work, defined as $1\,erg = 1\,dyne \times 1\,cm$, where $1\,joule = 10^7\,erg$.

Dimensional Formula of Work

The dimensional formula representing work, given by $[M L^2 T^{-2}]$.

Electron Volt ($eV$)

A unit of work or energy equal to $1.6 \times 10^{-19}\,J$.

Kilowatt Hour ($kWh$)

A unit of work or energy equal to $3.6 \times 10^6\,J$.

Work Done by Variable Force

The integral of force over displacement, calculated as $W = \int \vec{F} \cdot d\vec{s} = \int F_x\,dx + \int F_y\,dy + \int F_z\,dz$.

Work from Force-Displacement Graph

The total work done given by the area enclosed by the $F-S$ curve and the displacement axis, where area above the axis represents positive work and area below represents negative work.

Conservative Force

A force for which the work done around any closed path is zero and independent of the path taken (e.g., gravitational force, spring force).

Non-Conservative Force

A force for which the work done around a closed path is not equal to zero and depends on the path taken (e.g., friction, viscous force).

Potential Energy ($U$)

The energy possessed by a body by virtue of its position or configuration in a conservative force field, defined by $dU = -\vec{F} \cdot d\vec{r}$.

Kinetic Energy ($K$)

The energy possessed by a body by virtue of its motion, given by $K = \frac{1}{2}m v^2 = \frac{P^2}{2m}$, where $m$ is mass, $v$ is velocity, and $P$ is linear momentum.

Work-Energy Theorem

The principle stating that the net work done by all forces (conservative, non-conservative, internal, external, pseudo) acting on a body equals the change in its kinetic energy ($W_{net} = \Delta K = K_f - K_i$).

Law of Conservation of Mechanical Energy

States that the total mechanical energy ($U + K$) of a system remains constant if only conservative forces act on the system and work done by all other forces is zero.

Spring Force

A restoring force exerted by a spring given by $F_s = -k x$, where $k$ is the spring constant and $x$ is the deformation from its equilibrium length.

Potential Energy Stored in a Spring

The energy stored in a spring when deformed by $x$ from its natural length, given by $U = \frac{1}{2} k x^2$.

Stable Equilibrium

An equilibrium state where net force is zero ($\frac{dU}{dr} = 0$), potential energy $U$ is at a minimum, and $\frac{d^2 U}{dr^2} > 0$, causing restoring forces to return a displaced body back to equilibrium.

Unstable Equilibrium

An equilibrium state where net force is zero ($\frac{dU}{dr} = 0$), potential energy $U$ is at a maximum, and $\frac{d^2 U}{dr^2} < 0$, causing forces to push a displaced body further away from equilibrium.

Neutral Equilibrium

An equilibrium state where net force is zero ($\frac{dU}{dr} = 0$), potential energy $U$ remains constant at neighboring points, and $\frac{d^2 U}{dr^2} = 0$.

Work Done Pulling Hanging Chain onto Table

The work required to pull the $\frac{1}{n}$ hanging portion of a uniform chain of mass $M$ and length $L$ onto a frictionless horizontal table, given by $W = \frac{M g L}{2 n^2}$.

Power

The rate of doing work, defined as average power $P_{avg} = \frac{W}{t}$ or instantaneous power $P = \frac{dW}{dt} = \vec{F} \cdot \vec{v}$.

Horsepower ($H.P.$)

A unit of power equivalent to $746\,W$.

Critical Velocity at Highest Point (Vertical Circle)

The minimum speed required at the highest point of a vertical circular path of radius $r$ to complete the loop, given by $v_{top} = \sqrt{g r}$.

Critical Velocity at Lowest Point (Vertical Circle)

The minimum speed required at the lowest point of a vertical circular path of radius $r$ for a string-bound body to complete the loop, given by $v_{bottom} = \sqrt{5 g r}$.