Work, Energy and Power – Key Vocabulary

Vocabulary flashcards covering fundamental terms, units, formulas and concepts from the chapter on work, energy and power, including forms of energy, their interconversions and the principle of conservation of energy.

Work (Physics)

The product of the force applied on a body and the displacement of its point of application in the direction of the force; work is done only when displacement occurs.

Work Formula

W = F S cos θ, where F is force, S is displacement and θ is the angle between F and S.

Positive Work

Occurs when θ = 0°; force and displacement are in the same direction, so W = F S.

Zero Work

Happens when either displacement S = 0 or θ = 90° (force perpendicular to displacement); W = 0.

Negative Work

Occurs when θ = 180°; force opposes displacement, giving W = –F S.

Joule (J)

SI unit of work or energy; 1 J is work done by a force of 1 N moving an object 1 m in its direction.

erg

CGS unit of work; 1 erg = work done by 1 dyne over 1 cm; 1 J = 10⁷ erg.

Calorie

Heat energy needed to raise the temperature of 1 g of water from 14.5 °C to 15.5 °C; 1 cal = 4.18 J.

Kilowatt-hour (kWh)

Energy used by a 1 kW source in 1 h; 1 kWh = 3.6 × 10⁶ J.

Electron Volt (eV)

Energy gained by an electron accelerated through 1 V; 1 eV = 1.6 × 10⁻¹⁹ J.

Energy

The capacity of a body to do work; a scalar equal in magnitude to work it can perform.

Power

Rate of doing work or transferring energy; P = W / t.

Watt (W)

SI unit of power; 1 W = 1 J s⁻¹.

Kilowatt (kW)

1 kW = 10³ W.

Megawatt (MW)

1 MW = 10⁶ W.

Gigawatt (GW)

1 GW = 10⁹ W.

Horsepower (HP)

Engineering unit of power; 1 HP = 746 W.

Mechanical Energy

Sum of a body’s potential energy and kinetic energy; ME = U + K.

Potential Energy (U)

Energy possessed by a body due to its position or configuration.

Gravitational Potential Energy

Potential energy of a mass at height h: U = m g h.

Elastic Potential Energy

Energy stored in a deformed elastic body (compressed spring, stretched rubber, etc.).

Kinetic Energy (K)

Energy of motion; K = ½ m v².

Kinetic Energy–Momentum Relation

K = p² / 2m, where p is momentum.

Work-Energy Theorem

Work done by the net force on a body equals the change in its kinetic energy.

Translational Kinetic Energy

Kinetic energy due to straight-line motion of a body’s centre of mass.

Rotational Kinetic Energy

Energy of a body rotating about an axis (e.g., spinning wheel).

Vibrational Kinetic Energy

Energy due to to-and-fro motion about a mean position (e.g., vibrating string).

Principle of Conservation of Energy

Energy cannot be created or destroyed; it only transforms from one form to another, total energy remains constant.

Conservation of Mechanical Energy

In absence of non-conservative forces, K + U stays constant (e.g., freely falling body).

Conditions for Mechanical Energy Conservation

No external dissipative forces like friction or air resistance act on the system.

Force-Displacement Graph

For variable force, work equals the area under the F vs. S curve.

Power–Velocity Relation

For a constant force along motion: P = F v (force × average speed).

CGS Unit of Power

erg per second (erg s⁻¹); 1 W = 10⁷ erg s⁻¹.

Energy Dissipation / Degradation

Conversion of useful energy into an unavailable form (often heat) during transformations.

Simple Pendulum Energy Exchange

At extremes: all potential; at mean: all kinetic; total mechanical energy constant (ignoring air friction).

Solar Energy

Radiant energy emitted by the sun, harnessed via panels, furnaces or solar cells.

Heat Energy

Internal energy transferred due to temperature difference; released by combustion or sun.

Light Energy

Visible radiant energy enabling sight; produced by lamps, sun, flames, etc.

Chemical Energy

Energy stored in chemical bonds of fuels, food, batteries—released in reactions.

Hydro Energy

Kinetic and potential energy of moving or falling water used to drive turbines.

Electrical Energy

Energy of moving electric charges; supplied by cells, generators, power grids.

Nuclear Energy

Energy released from atomic nuclei via fission or fusion (E = m c²).

Geothermal Energy

Heat energy stored within Earth, driving hot springs and steam used for power.

Wind Energy

Kinetic energy of moving air masses harnessed by wind turbines.

Sound Energy

Energy carried by vibrating matter, perceived as sound when reaching ears.

Magnetic Energy

Energy associated with magnetic fields, enabling magnets to do work on ferromagnetic materials.

Generator (Dynamo)

Device converting mechanical energy into electrical energy.

Electric Motor

Machine converting electrical energy into mechanical (rotational) energy.

Electric Heater

Appliance transforming electrical energy into heat via resistance wires.

Loudspeaker

Device converting electrical signals into sound energy.

Microphone

Transducer converting sound energy into electrical signals.

Photosynthesis

Process in green plants converting light energy into chemical energy of food.

Solar Cell (Photovoltaic Cell)

Semiconductor device converting light (solar) energy directly into electrical energy.