Chapter Three: Energy - Vectors and Two-Dimensional Motion

A set of vocabulary flashcards defining key concepts, units, and theorems of energy, work, and power as presented in the lecture notes.

Work ($W$)

Done only if an object is moved through some displacement while a force is applied to it; defined for a constant force as $W = (F \text{cos}(\theta))\text{Δ}x$.

Joule ($J$)

The SI unit of work, where $1\,J = 1\,N \cdot m = 1\,kg \cdot m^2/s^2$.

foot ∙ pound ($ft \cdot lb$)

The US Customary unit for work which has no special name.

Kinetic Energy ($KE$)

The energy associated with the motion of an object of mass $m$ moving with a speed $v$, calculated as $KE = \frac{1}{2}mv^2$.

Work-Kinetic Energy Theorem

The principle stating that when work is done by a net force on an object and the only change is its speed, the work done is equal to the change in kinetic energy ($W_{net} = \Delta KE$).

Conservative Force

A force where the work done moving an object between two points is independent of the path taken, such as gravity, spring force, or electromagnetic forces.

Nonconservative Force

A force where the work done on an object depends on the path taken between its starting and final points, such as kinetic friction or air drag.

Gravitational Potential Energy ($PE_g$)

The energy associated with the relative position of an object in space near the Earth’s surface, expressed as $PE = mgy$.

Reference Level

An arbitrary location chosen for a problem where the gravitational potential energy is set to zero; commonly the Earth’s surface.

Conservation of Mechanical Energy

A principle stating that the total mechanical energy (sum of kinetic and potential energies) remains constant throughout any physical process in the absence of nonconservative forces.

Hooke’s Law

The relationship giving the restoring force of a spring as $F_s = -kx$, where $k$ is the spring constant and $x$ is the displacement.

Elastic Potential Energy ($PE_s$)

Potential energy related to the work required into compressing or stretching a spring from its equilibrium position, calculated as $PE_s = \frac{1}{2}kx^2$.

Power ($P$)

The rate at which energy transfer takes place, defined as $P = \frac{W}{\Delta t}$.

Watt ($W$)

The SI unit of power, equivalent to one Joule per second ($1\,J/s$).

Instantaneous Power

The rate of energy transfer at a specific moment, calculated by $P = F v$ when the force and velocity are parallel.

Kilowatt hours ($kWh$)

A unit of energy, not power, commonly used in electric bills.

Work Done by a Varying Force

The work done by a variable force acting on an object, which is equal to the area under the graph of $F_x$ versus $x$.