The three classes of lever and their mechanical advantage, the analysis of angular motion including moment of inertia and angular momentum, and the factors affecting the horizontal and vertical components of projectile motion.

What this dot point is asking

AQA wants you to identify the three classes of lever in the body, work out their mechanical advantage, analyse angular motion using moment of inertia and angular momentum, and explain the factors that affect the horizontal and vertical components of a projectile's flight path.

Lever systems

A reliable way to remember the order is the mnemonic for what sits in the middle, 1-2-3 = F-L-E: first class has the Fulcrum in the middle, second class the Load, third class the Effort. Because most body levers are third class, the body is built for large, fast ranges of movement at the cost of mechanical advantage, which is why muscles must generate large forces to move comparatively light loads quickly.

Angular motion

Angular motion is rotation about an axis. The moment of inertia ($I$) is the resistance of a body to a change in its state of rotation; it increases when mass is spread further from the axis. Angular velocity ($\omega$) is the rate of rotation, and angular momentum is $L = I\omega$.

Because there is no external rotational force in the air, angular momentum is conserved. A trampolinist who tucks moves mass closer to the axis, reducing $I$, so $\omega$ increases and they spin faster; opening out raises $I$ and slows the spin to control the landing.

Projectile motion

A projectile (a thrown or struck object, or the body in flight) follows a parabolic path. Its motion has two independent components:

• The horizontal component of velocity stays constant (ignoring air resistance), so it determines the distance.
• The vertical component is changed by gravity, decreasing on the way up and increasing on the way down.

The flight path and distance depend on three release factors: the angle of release (around 45 degrees for maximum range when release and landing heights are equal), the speed (velocity) of release and the height of release. For shorter, faster events such as a shot put, the optimum angle is below 45 degrees (typically 38 to 42 degrees) because the release height is above the landing height, which gives extra flight time.

AQA also expects you to interpret the parabola of flight in terms of the two forces acting once an object is airborne (ignoring air resistance): weight acts vertically down throughout, while there is no horizontal force, so the horizontal velocity is constant and only the vertical velocity changes. When weight is the dominant or only force, the path is a true symmetrical parabola. For light objects with a large surface area, such as a shuttlecock or a discus, air resistance is significant and distorts the path into an asymmetric curve, with the descent steeper than the ascent. Drawing the resultant force, the horizontal and vertical components, and the parabolic path is a common diagram question.