---
title: "Forces & Motion"
description: "75 topics in Science, in the order they build on each other."
canonical: https://lightmysky.com/learn/science/areas/forces-and-motion
source: https://lightmysky.com/learn/science/areas/forces-and-motion.md
retrieved: 2026-10-19
---

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# Forces & Motion

75 topics in Science, in the order they build on each other.

Page: https://lightmysky.com/learn/science/areas/forces-and-motion

- [Forces Vocabulary](https://lightmysky.com/learn/science/forces-vocabulary-mt_GBY8enpzO0): Name and describe forces using precise vocabulary (force, push, pull, twist, stretch, squash, contact force, non-contact force, gravity, weight, friction, air resistance, upthrust), and distinguish between forces that require physical contact and forces that act at a distance
- [Drawing Force Diagrams](https://lightmysky.com/learn/science/drawing-force-diagrams-mt_k7GOtslF-x): Draw forces acting on one object as labelled arrows. Arrow length shows relative force size and arrow direction shows force direction. For two forces along one line, equal and opposite forces balance. Combine forces to find the resultant, which changes motion when it is not zero. Draw the resultant separately from the individual forces.
- [Pushes & Pulls](https://lightmysky.com/learn/science/pushes-and-pulls-mt_B3W5EfimJw): Understand that pushes and pulls are forces that can change the speed or direction of an object's motion, and compare the effects of different strengths and directions
- [Testing Push & Pull Designs](https://lightmysky.com/learn/science/testing-push-and-pull-designs-mt_RlILL2sccX): Analyse data to determine if a design solution works as intended to change the speed or direction of an object with a push or pull
- [Friction & Surfaces](https://lightmysky.com/learn/science/friction-and-surfaces-mt_-p_xp4hMvh): Compare how things move on different surfaces, noticing that some surfaces create more friction than others
- [Contact & Non-Contact Forces](https://lightmysky.com/learn/science/contact-and-non-contact-forces-mt_lcf8lx-LkZ): Notice that some forces need contact between two objects (contact forces) while magnetic forces can act at a distance (non-contact forces)
- [Balanced & Unbalanced Forces](https://lightmysky.com/learn/science/balanced-and-unbalanced-forces-mt_3WMADSy0mA): Plan and conduct an investigation to provide evidence of the effects of balanced and unbalanced forces on the motion of an object
- [Force & Motion Vocabulary](https://lightmysky.com/learn/science/force-and-motion-vocabulary-mt_F3ATPTCYm6): Use technical vocabulary for force and motion — balanced forces, unbalanced forces, resultant force, acceleration, deceleration, speed, moment, lever, fulcrum, mechanical advantage — and apply these when explaining and predicting how forces affect the motion and position of objects
- [Gravity & Falling Objects](https://lightmysky.com/learn/science/gravity-and-falling-objects-mt_AvrQauS_zX): Explain that unsupported objects fall towards the Earth because of the force of gravity acting between the Earth and the falling object
- [Air Resistance & Friction](https://lightmysky.com/learn/science/air-resistance-and-friction-mt_Y9k86G8BBT): Identify the effects of air resistance, water resistance, and friction, and understand that these forces act between moving surfaces to oppose motion
- [Levers, Pulleys & Gears](https://lightmysky.com/learn/science/levers-pulleys-and-gears-mt_Q2k3fSwyzQ): Recognise that some mechanisms including levers, pulleys, and gears allow a smaller force to have a greater effect
- [Mass vs Weight](https://lightmysky.com/learn/science/mass-vs-weight-mt_sUVeVXzRuq): Distinguish between mass (amount of matter, measured in kg) and weight (gravitational force, measured in N), use the equation weight = mass × gravitational field strength, and explain why g differs on other planets and stars
- [Reading Distance-Time Graphs](https://lightmysky.com/learn/science/reading-distance-time-graphs-mt_OUv-QXmW7_): Read and plot distance-time graphs for moving objects; interpret the gradient (steepness) of a line as speed; identify stationary periods (horizontal sections), constant speed (straight diagonal lines), and relative speeds by comparing gradients; calculate average speed from the gradient of a straight-line segment using speed = distance ÷ time
- [Predicting Motion Patterns](https://lightmysky.com/learn/science/predicting-motion-patterns-mt_AlLYwCm92a): Make observations and measurements of an object's motion to provide evidence that a pattern can be used to predict future motion
- [Resultant Forces](https://lightmysky.com/learn/science/resultant-forces-mt_AiWlJfvC3O): Describe forces as vector quantities with both magnitude and direction, distinguish between balanced forces (zero resultant, no change in motion) and unbalanced forces (non-zero resultant, causes acceleration or deceleration)
- [Speed & Distance-Time Graphs](https://lightmysky.com/learn/science/speed-and-distance-time-graphs-mt_q-1a86ydgU): Calculate average speed using the equation speed = distance ÷ time, represent journeys on distance-time graphs, and interpret gradient as speed and flat sections as stationary periods
- [Relative Motion](https://lightmysky.com/learn/science/relative-motion-mt_-OndzpVsrv): Explain relative motion, how the apparent speed and direction of an object depends on the observer's own motion, using everyday examples such as trains and cars passing
- [Deformation & Fluid Pressure](https://lightmysky.com/learn/science/deformation-and-fluid-pressure-mt_fkwcCB5px7): Explain elastic and inelastic deformation, thermal expansion and contraction, and how pressure in still fluids acts in all directions and increases with depth
- [Moments, Pressure & Hooke's Law](https://lightmysky.com/learn/science/moments-pressure-and-hookes-law-mt_vuNjYx3qOy): Calculate moments using force × perpendicular distance, explain pressure transmission in enclosed liquids and atmospheric pressure, and describe spring extension, Hooke's Law, the limit of proportionality and the elastic limit.
- [Newton's First & Second Laws](https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J): State and apply Newton's First Law (an object stays at rest or constant velocity unless acted on by a resultant force) and Second Law (force = mass × acceleration), including the relationship between mass, force, and acceleration
- [Investigating Forces](https://lightmysky.com/learn/science/investigating-forces-mt_xkn2sf93WJ): Plan and carry out investigations into forces, including measuring force with a newton meter, investigating Hooke's Law, and collecting and interpreting motion data to test Newton's laws
- [Newton's Third Law](https://lightmysky.com/learn/science/newtons-third-law-mt_fbYbe3YSVj): State and apply Newton's Third Law: every force has an equal and opposite reaction force acting on a different object, distinguishing action-reaction pairs from balanced forces
- [Newton's Second Law with Numbers](https://lightmysky.com/learn/science/newtons-second-law-with-numbers-mt_Nn2MVJL7bO): Treating F = ma as a working equation: the resultant force sets the acceleration, and mass measures how strongly an object resists that change. Mass, not weight, is what appears in the calculation.
- [Terminal Velocity](https://lightmysky.com/learn/science/terminal-velocity-mt_3eNYHV-m-c): Drag grows as an object speeds up, so the resultant force shrinks and the acceleration fades to zero. From then on the object falls at a steady speed, which changes if its area or weight changes.
- [Momentum and Its Conservation](https://lightmysky.com/learn/science/momentum-and-its-conservation-mt_Nn5_DMbK1_): Momentum is mass times velocity, and it points the way the object moves. With no outside force, the total momentum of a group of objects is the same after a collision or explosion as before.
- [Vectors, Scalars and Free-Body Diagrams](https://lightmysky.com/learn/science/vectors-scalars-and-free-body-diagrams-mt_erzORFj2-1): Sorting quantities into scalars, which carry only a size, and vectors, which carry a direction too. Every force on one object is then drawn as an arrow whose length is its size, and the resultant is read off the diagram.
- [Acceleration from Velocity-Time Graphs](https://lightmysky.com/learn/science/acceleration-from-velocity-time-graphs-mt_nmvfbSgnOn): Read acceleration from the gradient of a velocity-time graph. Signed area gives displacement; adding the magnitudes of areas gives distance travelled. Interpret positive and negative gradients using the sign of velocity, since a negative gradient does not always mean slowing down.
- [The Uniform Acceleration Equations](https://lightmysky.com/learn/science/the-uniform-acceleration-equations-mt_yJMJQ8_KqR): Using v = u + at and v squared = u squared + 2as when acceleration is steady, including picking which one fits the quantities given. The graph work becomes algebra that answers questions no graph was drawn for.
- [Impulse and Crash Safety](https://lightmysky.com/learn/science/impulse-and-crash-safety-mt_BjLAFw2zjU): Force equals the change in momentum divided by the time it takes. Stretching a collision over a longer time lowers the force, which is what airbags, crumple zones and crash mats are for.
- [Stopping Distances and Braking Energy](https://lightmysky.com/learn/science/stopping-distances-and-braking-energy-mt_nRNZS4jHoj): Stopping distance splits into thinking distance, set by reaction time and speed, and braking distance, set by the work the brakes must do to empty the kinetic store. Braking distance grows with the square of the speed.
- [Moments, Couples and the Conditions for Equilibrium](https://lightmysky.com/learn/science/moments-couples-and-the-conditions-for-equilibrium-mt_EDsdTZ0BNO): A rigid body is in equilibrium when the resultant force is zero and the total moment about any point is also zero. A couple is the special case with no resultant force at all, only a turning effect.
- [Elastic and Inelastic Collisions](https://lightmysky.com/learn/science/elastic-and-inelastic-collisions-mt_JMwUuh1YUq): Momentum is conserved in every collision, but kinetic energy is conserved only in an elastic one. Adding up the kinetic energy before and after is what sorts one kind from the other.
- [The Centre of Mass and the Motion of a System](https://lightmysky.com/learn/science/the-centre-of-mass-and-the-motion-of-a-system-mt_fHO_KrMNKo): The centre of mass of any system moves as if all the mass sat there and every external force acted on it, whatever the internal forces do. Internal forces cancel in pairs, which is why an exploding shell keeps its parabola.
- [Variable Mass and the Rocket Equation](https://lightmysky.com/learn/science/variable-mass-and-the-rocket-equation-mt_4IugclcEVi): A rocket accelerates by throwing mass backwards, so the second law has to be applied to a system whose mass is changing. Integrating gives a speed that depends on exhaust speed and the logarithm of the mass ratio.
- [Newton's Law of Gravitation and Gravitational Field Strength](https://lightmysky.com/learn/science/newtons-law-of-gravitation-and-gravitational-field-strength-mt_uUYXl3L0oW): Any two masses attract with a force that falls off as the square of their separation. Dividing that force by the test mass leaves a field strength that belongs to the source alone.
- [Gravitational Potential and Escape Speed](https://lightmysky.com/learn/science/gravitational-potential-and-escape-speed-mt_drqTwCD9W8): Gravitational potential is the signed external work per kilogram to move a small mass slowly from infinity to a point. With zero at infinity it is negative. Escape speed is the minimum outward launch speed that reaches infinity under gravity alone, without drag or collision.
- [Magnetic Materials](https://lightmysky.com/learn/science/magnetic-materials-mt_9NvuqZKNiV): Observe how magnets attract or repel each other and attract some materials and not others
- [Magnetic Poles](https://lightmysky.com/learn/science/magnetic-poles-mt_jgNB2752b9): Describe magnets as having two poles (north and south) and predict whether two magnets will attract or repel based on which poles face each other
- [Magnetic Fields](https://lightmysky.com/learn/science/magnetic-fields-mt_56aspHjU19): Describe magnetic poles (north and south), explain attraction and repulsion between poles, describe magnetic field lines plotted using a compass, and explain the Earth's magnetic field and its practical uses
- [Electromagnets](https://lightmysky.com/learn/science/electromagnets-mt_2qkn8Lhc8e): Describe the magnetic field made by a current and investigate how electromagnet strength depends on current, coil turns and core material, within safe limits.
- [Motors & the Motor Effect](https://lightmysky.com/learn/science/motors-and-the-motor-effect-mt__7BVYUN180): Explain the motor effect as the force on a current-carrying conductor in a magnetic field, and describe how this principle is used in electric motors and loudspeakers
- [Floating, Sinking and Upthrust](https://lightmysky.com/learn/science/floating-sinking-and-upthrust-mt_TJI95Ot-qQ): Water pushes up on anything placed in it, and whether an object floats depends on that upward push against its weight rather than on how heavy it feels in the hand. A heavy steel boat floats and a small steel nail sinks, which is the puzzle this stop settles.
- [Pressure in Liquids and the Atmosphere](https://lightmysky.com/learn/science/pressure-in-liquids-and-the-atmosphere-mt_eLGNkEJAZl): Pressure is force spread over area. In a still fluid, pressure increases with depth and fluid density. Pressure differences explain upthrust; average object density helps predict floating, and air pressure falls with altitude.
- [Circular Motion: Angular Speed and Centripetal Force](https://lightmysky.com/learn/science/circular-motion-angular-speed-and-centripetal-force-mt_PW1G6nYStq): An object going round at steady speed is still accelerating, because the direction of its velocity keeps changing. The resultant force points to the centre and has size mv squared over r, which is also m omega squared r.
- [Simple Harmonic Motion: the Defining Relation and Its Graphs](https://lightmysky.com/learn/science/simple-harmonic-motion-the-defining-relation-and-its-graphs-mt_NTDayHkdfh): When the acceleration of an object is proportional to its displacement and points back towards the centre, the motion repeats with a period that does not depend on the amplitude. Displacement, velocity and acceleration then run as three sine curves each a quarter cycle ahead of the last.
- [Energy in Simple Harmonic Motion, Damping and Resonance](https://lightmysky.com/learn/science/energy-in-simple-harmonic-motion-damping-and-resonance-mt_3sh7E7k7j2): An oscillator trades its whole energy between a kinetic store and a potential one twice per cycle, and the total stays fixed only while nothing dissipates. Damping drains it, and driving at the natural frequency pumps the amplitude up until the losses catch the input.
- [Rotational Kinematics and the Angular Velocity Vector](https://lightmysky.com/learn/science/rotational-kinematics-and-the-angular-velocity-vector-mt_2UqK-zViqf): Angular displacement, velocity and acceleration are defined by the same derivatives as their linear partners, and angular velocity points along the axis. Every point of a rigid body then has a linear speed set by its distance from that axis.
- [Resolving Vectors into Components](https://lightmysky.com/learn/science/resolving-vectors-into-components-mt_tc698unGJG): Splitting one vector into two perpendicular parts with sine and cosine, then adding several vectors by adding their components. Scale drawing gives way to a method that stays exact however many forces act.
- [Newton's Second Law on a Slope](https://lightmysky.com/learn/science/newtons-second-law-on-a-slope-mt_OR_sKFelnP): Resolving weight along and perpendicular to a slope turns an inclined-plane problem into one equation of motion plus one balance. Friction enters as a force set by the normal contact force and the surfaces in contact.
- [Connected Bodies: Tension, Pulleys and Lifts](https://lightmysky.com/learn/science/connected-bodies-tension-pulleys-and-lifts-mt_qk2gn4tUoN): Two bodies joined by a rope share one acceleration, so each gets its own equation and the tension appears in both. Adding the pair of equations removes the tension, and substituting back returns it.
- [Projectile Motion as Two Independent Motions](https://lightmysky.com/learn/science/projectile-motion-as-two-independent-motions-mt_OBgL97RFbb): The horizontal and vertical motions of a projectile are worked separately: constant velocity across, uniform acceleration down, sharing nothing but the time. A ball rolled off a bench becomes two one-dimensional problems joined by t.
- [Projectiles Launched at an Angle](https://lightmysky.com/learn/science/projectiles-launched-at-an-angle-mt_MMuacyCqb8): An angled launch gives both directions a starting velocity, so flight time, greatest height and range all come from the same two lists. The symmetry of the path is a check on the answer rather than an extra rule.
- [Velocity and Acceleration as Derivatives](https://lightmysky.com/learn/science/velocity-and-acceleration-as-derivatives-mt_RdhbiJ6CTk): Velocity is the time derivative of the position vector and acceleration the derivative of velocity, taken one component at a time. Motion whose acceleration changes needs no new formulas once this is the definition.
- [Recovering Motion by Integrating Acceleration](https://lightmysky.com/learn/science/recovering-motion-by-integrating-acceleration-mt_CXo7wKOA46): Given acceleration as a function of time, integration returns velocity and then position, with the constants of integration fixed by the initial conditions. The constant-acceleration equations reappear as the case of a constant integrand.
- [Newton's Second Law as a Differential Equation](https://lightmysky.com/learn/science/newtons-second-law-as-a-differential-equation-mt_LzSNSkEovH): Writing the second law as mass times the second derivative of position equals force turns a force rule into an equation whose solution is the whole future motion. The same statement covers a falling stone, a spring and a charged particle.
- [Drag and Terminal Speed from the Equation of Motion](https://lightmysky.com/learn/science/drag-and-terminal-speed-from-the-equation-of-motion-mt_In6VeoADzZ): A drag force that grows with speed makes acceleration depend on velocity, and solving that equation gives an approach to a terminal speed. Linear and quadratic drag give different curves and different terminal values.
- [Simple Harmonic Motion as a Second-Order Equation](https://lightmysky.com/learn/science/simple-harmonic-motion-as-a-second-order-equation-mt_HHmR-uCvwO): Any restoring force proportional to displacement gives the same differential equation, whose solutions are sines and cosines at one natural frequency. Amplitude and phase come from the initial conditions, never from the equation itself.
- [Continuity and Bernoulli's Equation for Ideal Flow](https://lightmysky.com/learn/science/continuity-and-bernoullis-equation-for-ideal-flow-mt_pKxlVYTy0Y): For steady incompressible flow in an unbranched pipe, continuity links cross-section and speed. Applying the work-energy theorem to a fluid element relates pressure, speed and height along a streamline under ideal-flow assumptions.
- [Damped Oscillations and the Three Damping Regimes](https://lightmysky.com/learn/science/damped-oscillations-and-the-three-damping-regimes-mt_JCpYpFVn6s): Adding a velocity-dependent damping term splits the behaviour into underdamped, critically damped and overdamped, decided by the size of the damping against the natural frequency. Car suspensions and door closers are engineered choices between those regimes.
- [Driven Oscillations, Resonance and the Quality Factor](https://lightmysky.com/learn/science/driven-oscillations-resonance-and-the-quality-factor-mt_FmpOTEZFy4): After transients fade, a damped linear oscillator follows the driving frequency. Light damping gives a displacement-amplitude peak near the undamped natural frequency and a long free ring-down. High quality factor means weak damping; sufficiently strong damping removes the positive-frequency displacement peak.
- [Coupled Oscillators and Normal Modes](https://lightmysky.com/learn/science/coupled-oscillators-and-normal-modes-mt_vnTGOIqZzP): Two masses joined by springs no longer have one frequency: the motion splits into normal modes, each a pattern of the whole system oscillating at a single frequency. Any starting motion is a combination of those modes.
- [Moment of Inertia by Integration and the Parallel-Axis Theorem](https://lightmysky.com/learn/science/moment-of-inertia-by-integration-and-the-parallel-axis-theorem-mt_VFRk1WIzAK): Moment of inertia is an integral of distance squared over the mass distribution, so it depends on the axis as well as the body. The parallel-axis theorem moves a known result to any parallel axis without redoing the integral.
- [Rotational Dynamics and Rolling Without Slipping](https://lightmysky.com/learn/science/rotational-dynamics-and-rolling-without-slipping-mt_1mV6ukwDxK): Torque equals moment of inertia times angular acceleration, and a rolling body ties its rotation to its translation through one constraint. That constraint is what makes a hoop lose a race to a solid cylinder.
- [Angular Momentum and Its Conservation](https://lightmysky.com/learn/science/angular-momentum-and-its-conservation-mt_9v3S9-rhwc): Angular momentum is defined for a particle by its position and momentum and for a rigid body by its moment of inertia and angular velocity, and it changes only when an external torque acts. A skater pulling in her arms and a gyroscope precessing are the same law seen twice.
- [The Two-Body Problem, Orbital Energy and Kepler's First Two Laws](https://lightmysky.com/learn/science/the-two-body-problem-orbital-energy-and-keplers-first-two-laws-mt_CjHFftkB6M): Two bodies bound by gravity both orbit their common centre of mass, and the problem reduces to one body moving in a central field. Conservation of angular momentum gives the equal-areas law directly, and the sign of the total energy decides whether the path closes into an ellipse or escapes.
- [Viscosity, Poiseuille Flow and the Reynolds Number](https://lightmysky.com/learn/science/viscosity-poiseuille-flow-and-the-reynolds-number-mt_-1sWgkRtMs): Viscosity resists relative motion between fluid layers. Steady, fully developed, pressure-driven laminar flow of an incompressible Newtonian fluid in a uniform circular tube with stationary, no-slip walls has a parabolic speed profile. For a horizontal tube, Poiseuille's law relates flow rate to pressure difference, radius, length and viscosity. Reynolds number indicates the likely flow regime; it does not establish that Bernoulli's loss-free model applies.
- [Generalised Coordinates and the Lagrangian](https://lightmysky.com/learn/science/generalised-coordinates-and-the-lagrangian-mt_9QPk1zI9jE): Generalised coordinates that respect the constraints let ideal constraint forces drop out of the equations, because their virtual work at fixed time is zero even though the forces are still present. The Lagrangian is kinetic minus potential energy written in those coordinates. A pendulum needs one angle rather than two positions plus a tension.
- [The Euler-Lagrange Equation and Conserved Momenta](https://lightmysky.com/learn/science/the-euler-lagrange-equation-and-conserved-momenta-mt_GSEFABbEXI): Applying the Euler-Lagrange equation to a Lagrangian returns the equation of motion, and a coordinate missing from the whole Lagrangian gives a conserved momentum when no nonconservative generalized force acts in it. Conservation laws stop being separate rules and become consequences of symmetry.
- [Hamilton's Principle and the Action](https://lightmysky.com/learn/science/hamiltons-principle-and-the-action-mt_a273REeeGu): The paths a system can actually follow between fixed endpoints and times are those that make the action stationary, and the Euler-Lagrange equations are the condition for that. Stating mechanics as a claim about whole paths rather than about instants is what carries over to fields and to quantum theory.
- [The Hamiltonian, Phase Space and the Canonical Equations](https://lightmysky.com/learn/science/the-hamiltonian-phase-space-and-the-canonical-equations-mt_9bMDXQiq_n): Trading velocities for momenta turns one second-order equation per coordinate into two first-order ones, and makes phase space the natural arena. An autonomous Hamiltonian is conserved along the motion, and it equals the physical energy T + V for ordinary time-independent coordinates with a natural Lagrangian.
- [Magnetic Flux Density and the Force on a Current-Carrying Wire](https://lightmysky.com/learn/science/magnetic-flux-density-and-the-force-on-a-current-carrying-wire-mt_zuqc4gjBVh): The strength of a magnetic field is defined by the force it produces: F = BIL when the wire is at right angles to the field, and BIL sin theta otherwise. One tesla is one newton per amp per metre.
- [Charged Particles Moving in a Magnetic Field](https://lightmysky.com/learn/science/charged-particles-moving-in-a-magnetic-field-mt_evuhZ6cSfI): A particle moving at right angles to a uniform magnetic field experiences force of size B Q v, with Q as charge magnitude. The force stays perpendicular to velocity, producing a circle. Equating B Q v with m v squared / r gives r = (m v)/(B Q).
- [Poisson Brackets and Constants of the Motion](https://lightmysky.com/learn/science/poisson-brackets-and-constants-of-the-motion-mt_UFzJyZRdOI): For a quantity with no explicit time dependence, the Poisson bracket with the Hamiltonian gives its rate of change, so such a conserved quantity is one whose bracket vanishes. For the canonical examples, the bracket algebra reappears as the commutator in quantum mechanics.
- [Noether's Theorem: Symmetry and Conserved Quantities](https://lightmysky.com/learn/science/noethers-theorem-symmetry-and-conserved-quantities-mt_kAoOn8syBK): Every continuous symmetry of the action carries a conserved quantity, which is why translation gives total momentum and rotation about a fixed axis gives that component of angular momentum. Conservation laws stop being a list of separate facts.
- [From Coordinates to Fields: the Lagrangian Density](https://lightmysky.com/learn/science/from-coordinates-to-fields-the-lagrangian-density-mt_fRZN3ZByjr): A field has a value at every point, so the sum over coordinates becomes an integral of a Lagrangian density and the equations of motion become partial differential equations. The vibrating string is the case where the step can be checked against an answer already known.