Work, Energy, and Power Lecture Notes

Vocabulary practice flashcards covering the definitions, formulas, and units of work, energy, and power as presented in the lecture notes.

Work

The product of the force applied and the distance moved in the direction of the force; it is done only if the application of a force makes a body move from one point to another.

Joule (J)

The SI unit of work and energy. $1\,J$ is the amount of work done when a force of $1\,N$ moves a body through a displacement of $1\,m$ in the direction of force.

Work Done Expression

The mathematical calculation for energy transferred: $W = FS \cos(\theta)$, where the value depends on the angle $\theta$ between force and displacement.

Positive Work Done

Work occurring when $\theta < 90^{\circ}$, meaning there is a component of force in the direction of the object's displacement.

Negative Work Done

Work occurring when $\theta > 90^{\circ}$, such as when a body is moved over a rough horizontal surface and the frictional force acts against displacement.

Zero Work Done

The result when $\theta = 90^{\circ}$ (meaning $\cos(\theta) = 0$), such as when a man carries a load on his head while moving on a level road.

Energy

The capacity or ability of doing work.

Mechanical Energy

The energy associated with the motion and position or configuration of mechanical systems, encompassing both kinetic and potential energy.

Kinetic Energy

The energy possessed by a body by virtue of its motion, defined by the formula $K = \frac{1}{2}mv^2$.

Potential Energy

The energy possessed by a body by virtue of its position or configuration, such as shape or size.

Gravitational Potential Energy (G.P.E.)

The energy possessed by a body due to its position above the surface of the earth, equal to $mgh$.

Elastic Potential Energy

Potential energy associated with elastic materials, stored when work is done to compress or stretch a materials like a spring.

Linear Momentum ($p$)

The product of mass and velocity ($p = mv$), related to kinetic energy by the expression $K = \frac{p^2}{2m}$.

Work–Energy Theorem

The principle stating that the work done by the net force acting on a body is equal to the change in the kinetic energy of the body ($W = \Delta K.E$).

Conservative Force

A force where the amount of work done in moving an object is independent of the path taken, or where total work done over a closed path returning to the initial position is zero.

Non-conservative Force

A force where the work done by that force on an object moving between two points depends on the path taken between the points.

Law of Conservation of Energy

The principle that in any process, energy can be transformed from one form to another or transferred between bodies, but the total energy neither increases nor decreases.

Mass-Energy Relation

Einstein's theory that mass and energy are inter-convertible, given by the equivalence $E = mc^2$, where $c = 3 \times 10^8\,ms^{-1}$.

Power

The rate at which work is done, expressed as $P = \frac{W}{t}$ or as the dot product $P = F \cdot v = Fv \cos(\theta)$.

Watt (W)

The SI unit of power, where $1\,W$ is equal to doing $1\,J$ of work in $1\,s$.

Horse power (h.p.)

A unit of power where $1\,h.p. = 746\,W$.