Free Body Diagrams, Moments, and Equilibrium Vocabulary

Vocabulary flashcards covering free-body diagrams, various force types, resultant forces, equilibrium, density, pressure, upthrust, and moments based on the lecture material.

Free-body force diagram

A simplified diagram representing only the object itself and the forces acting on it, drawn at the points where they act with arrow lengths showing magnitude and direction.

Weight ($w$)

The force exerted on a body due to gravity, calculated as $w = mg$ where $m$ is mass and $g$ is gravitational field strength.

Normal contact force

The force that surfaces exert at $90^{\circ}$ to prevent solid objects from passing through each other.

Friction

A force that always acts in a direction to oppose any motion that would occur if the surface was completely smooth.

Resultant force

The sum of all the forces acting on a body when added together as vectors.

Equilibrium

A state in which the resultant force acting on an object is zero.

Vector diagram

A diagram where force arrows are joined tip-to-tail to add vectors and find the distance between the start and end points.

Closed polygon

The shape formed in a vector diagram when an object is in equilibrium, meaning the start point and end point are at the same place.

Density ($\rho$)

The mass per unit volume of an object, calculated using the equation $\rho = \frac{m}{V}$ with units in $kg\,m^{-3}$.

Pressure ($p$)

The force acting per unit area, calculated as $p = \frac{F}{A}$ and measured in $N\,m^{-2}$ or Pascals ($Pa$).

Pressure in a fluid

The pressure calculated as $p = \rho gh$, where $\rho$ is fluid density, $g$ is gravitational field strength, and $h$ is fluid depth.

Upthrust

An upwards force acting on a submerged object caused by the pressure difference between the top and bottom surfaces of the object in a fluid.

Archimedes Principle

States that an object submerged or floating in a fluid experiences an upthrust equal to the weight of the fluid displaced.

Centre of Gravity

The point of an object through which its weight acts; it can be determined experimentally using a plumb line from multiple pivots and finding their intersection point.

Stability

The resistance of an object to toppling, which can be increased by having a low centre of mass and a wide base.

Moment of a force

Also known as Torque, it is the product of the force $F$ and its perpendicular distance $d$ from the point of rotation, measured in $N\,m$.

Principle of Moments

States that for a body in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point.

Couple

A pair of parallel forces that have equal magnitude and opposite direction but act along different lines to produce rotational force.

Torque of a couple

The product of the magnitude of one of the forces $F$ and the perpendicular separation $d$ between the two forces ($\text{Torque} = Fd$).