Mass, Weight, and Newton's Laws of Motion

Mass: A scalar measurement of the amount of matter in an object, measured in kilograms ( $kg$ ).
Weight: The force ( $W$ ) experienced by mass due to gravitational attraction.
Formula: $W = m \times g$ * $W$ = weight ( $N$ ) * $m$ = mass ( $kg$ ) * $g$ = gravitational field strength ( $N\,kg^{-1}$ )
Gravitational Field Strength ( $g$ ): * Earth: Approximate GCSE value is $10\,N\,kg^{-1}$ (equivalent to $m\,s^{-2}$ ). * Moon: $1.6\,N\,kg^{-1}$ .
Variable Weight: Mass remains unchanged across different planets, but weight varies with $g$ . For example, a $0.2\,kg$ mug weighs $2\,N$ on Earth ( $0.2 \times 10$ ) but only $0.32\,N$ on the moon ( $0.2 \times 1.6$ ).
Weightlessness: Small objects in weak gravitational fields (distant space) appear weightless despite still possessing mass.

Definition: Inertial forces resist changes to an object's velocity or state of motion.
Mass Dependency: Inertia is directly proportional to mass; heavier objects require greater force to overcome inertia.

Newton's First Law: A body remains at rest or travels with uniform motion in a straight line unless acted upon by a resultant force (balanced forces).
Newton's Second Law: A resultant force ( $F$ ) causes acceleration ( $a$ ) proportional to mass ( $m$ ). * Formula: $F = m \times a$ * $F$ = resultant force ( $N$ ) * $m$ = mass ( $kg$ ) * $a$ = acceleration ( $m\,s^{-2}$ )
Newton's Third Law: When two objects interact, they exert equal and opposite forces on each other (Action and Reaction).

Mechanism: As an object moves through a fluid (air or water), drag forces increase until they equal the driving force.
Terminal Velocity: The constant speed reached when the resultant force becomes zero.
Skydiver Dynamics: * The driving force is weight ( $W = m \times g$ ). * Higher mass typically results in a higher terminal velocity, though increased surface area/drag can mitigate this. * Opening a parachute significantly increases drag, slowing the diver to a new, lower terminal velocity.