# Theme A: Space, time and motion

> IB Physics HL · IB Physics HL 2025+
> Source: https://www.owlsprep.com/study/ib-physics-hl-u1-overview/
> Weight: 14-16% of overall exam

This foundational unit covers core classical mechanics, extended with AHL topics in rotational motion, relativity and gravitation. It builds the problem-solving framework you will use across all other IB Physics HL units.

**Prerequisites:** Basic algebraic reasoning and introductory secondary-level motion concepts

## Learning objectives

- Describe and analyze motion in linear, rotational, and relativistic frames of reference
- Apply conservation laws for momentum and energy to solve a range of mechanical problems
- Connect core classical mechanics concepts to advanced AHL extensions for extreme regimes
- Solve problems involving circular motion, gravitation, and relativistic particle interactions

## Unit at a Glance

This unit follows a logical sequential learning arc: it starts by describing motion (kinematics), then explores what causes motion (forces), quantifies energy transfer, and finally extends core classical concepts to rotational, relativistic, and gravitational systems. Every sub-topic builds on the previous one, so mastery of early foundational topics is critical for success with later advanced AHL content.

The HL extension topics push classical mechanics into new regimes: relativistic energy and momentum for particles moving near the speed of light, and advanced treatments of orbital motion under gravitational force. This unit sets the core physical reasoning habits you will rely on for the rest of the course.

Ordered sub-topics for sequential learning:
- [A.1 Kinematics](https://www.owlsprep.com/study/ib-physics-hl-u1-a-1-kinematics/) — Describes 1D and 2D motion with displacement, velocity, acceleration, and projectile motion.
- [A.2 Forces and momentum](https://www.owlsprep.com/study/ib-physics-hl-u1-a-2-forces-and-momentum/) — Introduces Newton's laws and conservation of momentum for interactions and collisions.
- [A.3 Work, energy and power](https://www.owlsprep.com/study/ib-physics-hl-u1-a-3-work-energy-and/) — Covers work done, energy conservation, power, and efficiency for mechanical systems.
- [A.4 Rotational mechanics](https://www.owlsprep.com/study/ib-physics-hl-u1-a-4-rotational-mechanics/) — Extends linear mechanics concepts to rotation, including torque and rotational inertia.
- [A.5 Special relativity: energy and momentum (AHL)](https://www.owlsprep.com/study/ib-physics-hl-u1-a-5-special-relativity-energy/) — Explores relativistic momentum, energy, and mass-energy equivalence for high-speed particles.
- [A.6 Circular motion and gravitation (AHL)](https://www.owlsprep.com/study/ib-physics-hl-u1-a-6-circular-motion-and/) — Covers uniform circular motion, gravitational fields, orbits, and escape velocity.

## Common pitfalls

- **Wrong:** Mixing linear and rotational analog quantities in hybrid problems
  - Why it fails: Confusing symbols and formulas for linear vs rotational motion leads to calculation errors
  - Correct: Always label quantities as linear or rotational and match formulas to your motion type
- **Wrong:** Using classical momentum/energy formulas for relativistic problems
  - Why it fails: Classical formulas break down at speeds approaching $c$, leading to large inaccuracies
  - Correct: Use relativistic formulas for any object with speed $v > 0.1c$
- **Wrong:** Forgetting to account for gravitational potential energy in energy conservation problems
  - Why it fails: Neglecting potential energy changes leads to incorrect final energy values
  - Correct: Always include all forms of potential energy when applying conservation of energy

## Cheatsheet

| Concept / Formula | Description |
| --- | --- |
| $v = u + at$ | First kinematic equation for constant acceleration |
| $\triangle p = F_{net} \triangle t$ | Impulse-momentum theorem |
| $\triangle E_{total} = W_{non-conservative}$ | Work-energy principle |
| $\tau = I \alpha$ | Newton's second law for rotational motion |
| $E^2 = (pc)^2 + (m_0 c^2)^2$ | Relativistic energy-momentum relation |
| $F_g = \frac{G M m}{r^2}$ | Newton's law of universal gravitation |

## What's next

Begin your learning with the first sub-topic of this unit, A.1 Kinematics, which lays the foundation for describing all types of motion. Mastery of each sequential sub-topic is critical, as every later topic builds on concepts from earlier in the unit. After completing all sub-topics in Theme A, you will progress to the next core unit of IB Physics HL.

- [A.1 Kinematics](https://www.owlsprep.com/study/ib-physics-hl-u1-a-1-kinematics/)
- [A.2 Forces and momentum](https://www.owlsprep.com/study/ib-physics-hl-u1-a-2-forces-and-momentum/)
- [A.3 Work, energy and power](https://www.owlsprep.com/study/ib-physics-hl-u1-a-3-work-energy-and/)

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