SI units
The International System of Units, or SI, provides a shared language for physical measurements.
Open lessonPhysics
Start with the foundations, follow a pathway or choose an idea that catches your attention. Every published lesson includes worked examples and checked practice.
Pathway 01 · 2 available
Measurement and scientific practice
Scalars and vectors
A scalar has magnitude only. A vector has magnitude and direction.
Open lessonUpcoming topics: Unit conversion · Accuracy · Precision · Uncertainty · Scientific notation · Reading experimental data. These topics do not yet have standalone lessons.
Pathway 02 · 3 available
Motion
Speed and velocity
Average speed is total distance divided by elapsed time. Average velocity is displacement divided by elapsed time.
Open lessonAcceleration
Acceleration is the rate of change of velocity with time.
Open lessonMotion graphs
A motion graph shows how a quantity such as position or velocity changes with time.
Open lessonUpcoming topics: Distance and displacement · Equations of motion · Falling objects · Introductory projectile motion. These topics do not yet have standalone lessons.
Pathway 03 · 3 available
Forces
Newton’s laws
Newton’s laws connect forces to changes in motion and describe how interacting objects exert forces on each other.
Open lessonMass and weight
Mass measures inertia and is measured in kilograms. Weight is the gravitational force on a mass, measured in newtons.
Open lessonFriction and resultant force
Friction is a contact force that opposes relative sliding, or the tendency to slide, between surfaces.
Open lessonUpcoming topics: Gravity · Normal force · Tension · Free-body diagrams · Momentum · Impulse. These topics do not yet have standalone lessons.
Pathway 04 · 3 available
Energy
Work and energy transfer
Work is energy transferred by a force acting through a displacement.
Open lessonKinetic energy
Kinetic energy is energy associated with motion. For ordinary speeds, translational kinetic energy is ½mv².
Open lessonGravitational potential energy
Near Earth’s surface, a change in gravitational potential energy is mass × gravitational field strength × change in height.
Open lessonUpcoming topics: Power · Efficiency · Energy transfers · Conservation of energy. These topics do not yet have standalone lessons.
Pathway 05 · 2 available
Electricity
Current, voltage and Ohm’s law
Current is the rate of flow of charge. Voltage is energy transferred per unit charge. Resistance relates voltage to current for a component.
Open lessonElectrical power and energy
Power is the rate of energy transfer. Electrical power in a steady direct-current circuit is voltage multiplied by current.
Open lessonUpcoming topics: Series and parallel circuits · Household electricity safety. These topics do not yet have standalone lessons.
Pathway 06 · 1 available
Waves
Frequency and wavelength
Frequency counts cycles per second. Wavelength is the distance between matching points on adjacent wave cycles.
Open lessonUpcoming topics: Sound · Light · Reflection · Refraction · Interference. These topics do not yet have standalone lessons.
Pathway 07 · 1 available
Heat
Temperature and specific heat
Temperature describes thermal state. Specific heat capacity is the energy required to raise one kilogram of a substance by one kelvin.
Open lessonUpcoming topics: Thermal energy · Conduction · Convection · Radiation · Changes of state. These topics do not yet have standalone lessons.
Pathway 08 · 0 available
Pressure and fluids
Upcoming topics: Density · Pressure · Atmospheric pressure · Liquid pressure · Buoyancy · Hydraulics. These topics do not yet have standalone lessons.
Pathway 09 · 0 available
Space, gravity and atomic foundations
Upcoming topics: Gravitational force · Orbits · The Solar System · Atoms · Isotopes · Radiation · Half-life · Nuclear energy. These topics do not yet have standalone lessons.