Chapter 2: Forces and Moments

Practice vocabulary flashcards for H2/H1 Physics Chapter 2, covering fundamental forces, equilibrium conditions, and properties of various contact and non-contact forces.

Newton ($N$)

The magnitude of a force that acts on a mass of $1\,kg$ resulting in an acceleration of $1\,m/s^2$ in the direction of the force.

Field

A region of space in which a body experiences a force associated with the field.

Weight ($W$)

The gravitational force experienced by a body of mass $m$ in a gravitational field, expressed by the equation $W = mg$.

Centre of gravity (C.G.)

The single point at which the whole weight of a body may be considered to act.

Normal contact force

A force exerted perpendicular to surfaces that are physically touching.

Free Body Diagram (FBD)

A diagram showing all external forces acting on a body or system in isolation, omitting the environment and forces the object exerts on others.

Friction

A force that opposes relative motion or the tendency of relative motion between two surfaces in contact, acting parallel to the surfaces.

Viscous forces

Dissipative forces that act when there is relative motion between a body and the fluid (gas or liquid) surrounding the body.

Upthrust (Buoyancy force)

The net upward force exerted by a fluid on an object arising from the difference in pressure acting on the bottom versus the top of the object.

Hooke’s law

States that the extension (or compression) of a body is proportional to the applied force ($F = kx$), provided the limit of proportionality is not exceeded.

Force constant ($k$)

A measure of the stiffness of a spring, equal to the gradient of the force-extension ($F-x$) graph.

Elastic limit

The point beyond which a spring will not return to its natural length when the load is removed.

Translational equilibrium

A state where the sum of forces acting on an object in any direction is zero ($\sum F = 0$), resulting in zero acceleration.

Vector triangle

A closed triangle formed by the vector sum of three coplanar forces when the resultant force is zero.

Moment of a force ($\tau$)

The turning effect of a force, calculated as the product of the force and the perpendicular distance from the line of action of the force to the pivot ($\tau = F \times d_{\perp}$).

Couple

A pair of forces of equal magnitude but opposite direction whose lines of action do not coincide, tending to produce rotation only.

Torque of a couple

The product of one of the forces in a couple and the perpendicular distance between the lines of action of the two forces.

Rotational equilibrium

A state in which there is no resultant torque about any point ($\sum \tau = 0$).

Principle of Moments

States that for an object to be in rotational equilibrium, the sum of clockwise moments about any point must equal the sum of anti-clockwise moments about that same point.