Energy, Work, Kinetic and Potential Energy Flashcards

Vocabulary flashcards covering work, energy, kinetic energy, potential energy, and their formulas based on Theme 4 lecture materials.

Work (in Physics)

The condition in Physics where a force acts on a body and the body gets displaced in the direction of the force.

Conditions for Work Done

The two conditions required for work to be done: 1. There is a force acting on a body, and 2. The force causes displacement of the body in the direction of the force.

Zero Work (Perpendicular Displacement)

The work done when displacement is perpendicular to the direction of the applied force, such as a satellite orbiting Earth under gravity or a stone whirled by a string once rotational motion sets in.

Zero Work (No Displacement or No Force)

Situations where work is zero because either no force is applied (reading a book or ball resting on the ground) or no displacement occurs (pushing a wall or holding weights standing in one place).

Formula for Work

The equation $\text{work } (W) = \text{force } (F) \times \text{displacement } (s)$, representing the product of force and displacement in the direction of force.

Joule ($J$)

The SI unit of work and energy, also referred to as a newton-metre ($N m$), defined as the work done when a force of $1\,N$ displaces a body by $1\,m$ in the direction of force ($1\,J = 1\,N \times 1\,m$).

Kilojoule ($kJ$)

A unit of work or energy equal to $1000\,J$ ($1\,kJ = 1000\,J$).

Work Dependence on Force and Displacement

For a given force, work done increases with greater displacement; for a given displacement, work done increases with greater applied force.

Energy

The capacity to do work, measured in joules ($J$); a body gains energy when work is done on it and loses energy when work is done by it.

Kinetic Energy

The energy possessed by a body by virtue of its motion, derived from the Greek word "kinêtikos", which means 'to move'.

Kinetic Energy Formula

The relationship $\text{kinetic energy} = \frac{1}{2} (\text{mass}) \times (\text{speed})^2$ or $KE = \frac{1}{2} m v^2$.

Kinetic Energy Scaling Rules

If the mass of a body is doubled, its kinetic energy doubles; if the speed is doubled, its kinetic energy becomes four times.

Kinetic Energy Pendulum-Matchbox Experiment

An activity showing that releasing a heavier bob or releasing a bob with higher speed displaces a matchbox over a larger distance, proving $KE$ depends on mass and speed.

Potential Energy

The stored form of energy a body has due to its position or configuration, derived from the Latin word "potentia" meaning 'power'.

Elastic Substance

A substance or object (such as rubber, spring, or bowstring) that can be stretched or compressed by force and regains its size and shape after the force is removed.

Elastic Potential Energy

The energy stored in an elastic object when work is done by an applied force to deform it by stretching or compressing.

Gravitational Potential Energy

The energy possessed by a body due to its raised position with respect to the ground, equal to the work done against gravity in lifting it to that height.

Gravitational Potential Energy Formula

The relationship $W = P.E. = m g h$, where $m$ is mass, $g$ is acceleration due to gravity, and $h$ is height above the surface.