Work and Energy – Key Vocabulary

A set of vocabulary flashcards summarizing key terms and principles about work, energy, and conservative versus non-conservative forces from the lecture notes.

Potential Energy (PE, U)

Stored energy associated with an object’s position or configuration.

Gravitational Potential Energy (GPE)

Energy stored due to an object’s height above a reference level; equal to m g h.

Elastic (Spring) Potential Energy (EPE/SPE)

Energy stored when a spring or elastic material is stretched or compressed; equal to ½ k (Δx)².

Kinetic Energy (KE)

Energy of motion; equal to ½ m v².

Mechanical Energy (E)

Sum of an object’s kinetic and potential energies: E = KE + PE.

Energy Transformation

Conversion of energy from one form to another (e.g., GPE → KE).

Conservative Force

Force whose work is path-independent and can be related to a potential energy (e.g., gravity, spring force).

Non-Conservative Force

Force whose work depends on the path taken and has no associated potential energy (e.g., friction, air drag).

Path Independence

Property of conservative forces—work depends only on initial and final positions.

Path Dependence

Property of non-conservative forces—work depends on the actual route traveled.

Closed Path Work (Conservative)

Net work done by a conservative force around a closed loop is zero.

Closed Path Work (Non-Conservative)

Net work done by a non-conservative force around a closed loop is non-zero.

Work–Kinetic Energy Theorem

Net work done on an object equals the change in its kinetic energy: W = ΔKE.

Gravitational Work Expression

For gravity alone: WG = −m g (hf − h_0) = ΔKE = −ΔGPE.

Spring Work Expression

For an ideal spring: WS = −[½ k(Δxf)² − ½ k(Δx_0)²] = ΔKE = −ΔEPE.

Conservation of Mechanical Energy

When only conservative forces act, total mechanical energy remains constant (ΔE = 0).

External Non-Conservative Work (W_NC)

Work done by all non-conservative forces; equals the change in mechanical energy when W_NC ≠ 0.

Thermal Energy

Internal energy often produced by non-conservative forces, such as friction transforming KE into heat.

Coefficient of Kinetic Friction (μ_k)

Ratio that quantifies the frictional force between surfaces in relative motion: Ffriction = μk N.

Mechanical Energy Constant Condition

KE + PE remains constant if W_NC = 0 (no net external non-conservative work).

Energy Transfer (Slingshot Example)

Conversion of elastic potential energy to kinetic energy when a stretched band is released.

Energy Transfer (Diver Example)

Conversion of gravitational potential energy to kinetic energy as a diver falls.

Energy Transfer (Meteor Example)

Conversion of kinetic energy to thermal energy due to air resistance heating a meteor.

Potential Energy–Kinetic Energy Exchange

For conservative systems, a gain in KE equals an equal loss in PE, and vice versa.