Forces, Density, and Pressure Flashcards

Vocabulary flashcards covering key definitions, principles, and formulas for forces, equilibrium, density, and fluid pressure.

Uniform gravitational field

A gravitational field that exerts the same gravitational force on a mass everywhere within the field.

Weight ($F$)

The gravitational force exerted on an object, calculated using $F = m g$, where $m$ is mass and $g$ is gravitational field strength.

Gravitational field strength on Earth's surface

The constant acceleration due to gravity near Earth's surface, approximately equal to $9.81\,\text{N}\text{kg}^{-1}$.

Centre of gravity

The single point at which an object's weight is considered to act.

Uniform object

An object that has its centre of gravity located exactly at its geometric centre.

Moment of a force

The turning effect of a force about a point, calculated as $\text{Moment} = \text{Force} \times \text{Perpendicular distance to line of action of force from the point}$.

Couple

A pair of coplanar forces that are equal in magnitude and act in opposite directions, producing only rotation.

Torque of a couple

The turning moment generated by a couple, calculated as $\text{Moment of a couple} = \text{Force} \times \text{Perpendicular distance between the lines of action of forces}$.

Principle of moments

States that for an object in equilibrium, the sum of anticlockwise moments about a pivot equals the sum of clockwise moments about that same pivot.

Equilibrium (forces and torques)

The state of a system when there is no resultant force and no resultant torque acting on it.

Density ($\rho$)

A measure of how compact a substance is, defined as mass per unit volume and calculated using $\rho = \frac{m}{V}$.

Pressure ($p$)

The force perpendicular to a surface per unit area, calculated using $p = \frac{F}{A}$.

Fluid pressure change formula

The equation $\Delta p = \rho g \Delta h$, which gives the pressure exerted by a fluid column of density $\rho$ over height change $\Delta h$.

Total pressure

The overall pressure experienced by an object submerged in a fluid, equal to the sum of fluid pressure and atmospheric pressure ($\text{Total pressure} = \Delta p + \text{Atmospheric pressure}$).

Upthrust on a submerged cylinder

An upward force generated because the pressure at the deeper bottom face of the submerged cylinder is larger than the pressure at the top face.

Archimedes' Principle

States that the weight of the fluid displaced by a submerged body is equal to the upthrust force exerted on the body.

Buoyant force ($F$)

The upward upthrust force acting on an object submerged in a fluid, given by $F = \rho g V$, where $\rho$ is fluid density, $g$ is acceleration due to gravity, and $V$ is displaced fluid volume.