Kinematics
Displacement, Velocity & Acceleration · SUVAT Equations & Projectile Motion · Relative Motion & Frames of Reference
IB Physics HL topic guide
Space, Time and Motion
Space, Time and Motion is a core part of IB Physics HL. This guide connects the syllabus ideas behind Kinematics, Forces and Momentum, Work, Energy and Power, Rigid Body Mechanics, Galilean and Special Relativity, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.
What you will learn
Space, Time and Motion syllabus outline
The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.
Forces and Momentum
Newton's Laws of Motion · Momentum & Impulse · Friction, Drag and Terminal Velocity
Work, Energy and Power
Work and Energy · Power and Efficiency · Energy Sources and Transformations
Rigid Body Mechanics
Torque and Equilibrium · Rotational Dynamics · Rolling Motion and Rotational Energy
Galilean and Special Relativity
Galilean Relativity · Special Relativity: Postulates and Time Dilation · Length Contraction, Mass-Energy and Spacetime
Free worked preview
Torque and Equilibrium
This complete preview comes from the Rigid Body Mechanics unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.
Torque and Rotational Equilibrium
So far you have treated all objects as point particles — but real objects are extended, and forces applied off-centre cause rotation as well as translation. This lesson extends your mechanics toolkit from linear equilibrium () to rotational equilibrium (), which is essential for analysing bridges, cranes, ladders, and every structure that must not topple. When you finish you will be able to choose a pivot strategically, set up torque equations, and solve for unknown forces in any static rigid-body problem.
Torque (or moment of a force) is the turning effect of a force about a pivot. A larger force, acting further from the pivot, and more perpendicular to the lever arm, produces a greater torque:
where
torque (N m) — the rotational equivalent of force; positive if anticlockwise (by convention)
magnitude of the applied force (N)
distance from the pivot to the point where the force is applied (m) — the "lever arm"
angle between the force vector and the line from pivot to point of application; torque is maximum when θ = 90° (force perpendicular to lever arm)
Equivalently: τ = F × d⊥, where d⊥ is the perpendicular distance from the pivot to the line of action of the force.
Conditions for Static Equilibrium
Two Conditions
1. (net force = 0 in each direction)
2. (net torque = 0 about any chosen pivot)
1. (net force = 0 in each direction)
2. (net torque = 0 about any chosen pivot)
Pivot ChoiceAlways choose your pivot at the point where an unknown force acts — this eliminates that unknown from the torque equation entirely, simplifying the algebra significantly.
Worked Example — Ladder
A uniform ladder (mass 20 kg, length 4 m) leans against a smooth wall at 60° to the horizontal. Find the normal reaction at the wall.
Take pivot at base: Nwall × 4sin60° = mg × 2cos60°
Nwall = (20×9.81×2×0.5)/(4×0.866) = 196.2/3.46 = 56.7 N
Take pivot at base: Nwall × 4sin60° = mg × 2cos60°
Nwall = (20×9.81×2×0.5)/(4×0.866) = 196.2/3.46 = 56.7 N
Reviewed by the Study to Learn editorial team · Updated 2026-07-24