Year 8 Science: Forces, Interactions, Moments, and Gravity

Vocabulary practice flashcards covering forces, interaction pairs, Newton's laws, resultant forces, vectors, scalars, balanced forces, terminal velocity, moments, mass, weight, and gravitational fields.

Force

A push or a pull that can change the motion or shape of an object.

Contact Force

A force that occurs when two objects physically touch each other, such as friction or air resistance.

Non-Contact Force

A force that can act between objects across a distance without them touching, such as gravity, electrostatic force, or magnetic force.

Interaction Pair

A pair of forces of the same type and equal size (magnitude) that act in opposite directions on two different interacting objects.

Newton's Third Law of Motion

The law stating that for every action force, there is an equal and opposite reaction force.

Magnitude

The size or numerical amount of a physical quantity, represented by the length of a force or vector arrow.

Resultant Force

The single overall force that can replace all the individual forces acting on an object and have the same effect.

Scalar Quantity

A physical quantity that has magnitude (size) only and no direction, such as distance, mass, volume, temperature, and time.

Vector Quantity

A physical quantity that has both magnitude (size) and direction, such as force, velocity, displacement, and weight.

Displacement

The straight-line distance and direction from a given starting point to an end point; a vector quantity.

Balanced Forces

Forces acting on an object that are equal in size and opposite in direction, producing a resultant force of $0\,\text{N}$ and causing no change in motion.

Unbalanced Forces

Forces acting on an object that are not equal, producing a non-zero resultant force that causes the object to accelerate in the direction of the larger force.

Equilibrium

The state of an object when all the forces acting on it are balanced and cancel out, resulting in no change to its speed or direction of motion.

Newton's First Law of Motion

The principle stating that if all forces acting on an object are in equilibrium (balanced), a stationary object remains stationary and a moving object continues moving at a steady speed in the same direction.

Terminal Velocity

The steady, constant speed reached by a falling object when the upward drag force (air resistance) equals its downward weight, putting the object into equilibrium.

Centripetal Force

Any resultant force that acts toward the center of a circle to keep an object moving along a circular path by continuously changing its direction.

Drag

A frictional resistance force (such as air resistance or fluid resistance) that opposes the motion of an object moving through a fluid.

Pivot

The fixed point or axle about which an object turns or rotates.

Moment

The turning effect of a force about a pivot, calculated as $\text{moment} = \text{force} \times \text{perpendicular distance from the pivot}$ and measured in newton-metres ($\text{Nm}$).

Law of Moments

The principle stating that when an object is balanced (in equilibrium), the sum of the clockwise moments equals the sum of the anticlockwise moments.

Centre of Gravity

The single point through which the entire weight of an object appears to act (also known as the centre of mass).

Mass

The amount of matter (atoms) in an object, measured in kilograms ($\text{kg}$), which does not change based on location in the universe.

Weight

The attractive gravitational force acting on an object's mass, measured in newtons ($\text{N}$), which varies depending on gravitational field strength.

Gravitational Field

The region surrounding a massive body (such as Earth) in which any other object experiences an attractive gravitational force pulling it toward the center.

Gravitational Field Strength ($g$)

The force of gravity per unit of mass, measured in newtons per kilogram ($\text{N/kg}$), equal to approximately $9.8\,\text{N/kg}$ on the surface of Earth.