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Mechanics

Map

Arrows point from what you learn first to what it opens. Point at a concept to light up its chain and where it comes back deeper. Right-click a concept (or press and hold it) for its lessons and stories.

  • Proven to depth123
  • Open
  • Locked
  • Comes back deeper
Depth 2Depth 2Depth 2Depth 2AccelerationAir resistanceBalanced forcesCompassContact and non-contact forcesFloating and sinkingForceGravityHow planes flyInclined planeLeversMagnetsNewton's first lawNewton's second lawPositionPulleyScrewSimple machinesSlippery and roughThings that moveToolsVelocityWays of getting aroundWedgeWheel and axle

Learning path

In the order the concepts build on each other.

  1. Floating and sinkingReadySome things stay on top of water and others go to the bottom, and you can test which by trying.
  2. ForceReadyA push or a pull on an object. Forces have size and direction, and they are what changes motion.
  3. MagnetsReadyA magnet pulls things made of iron and steel, without touching them and even through paper. Every magnet has two ends called poles, north and south. Two different poles pull each other together; two poles that are the same push each other apart.
  4. PositionReadyWhere an object is, measured from a chosen origin along chosen directions. Every description of motion starts here.
  5. Things that moveReadyThings move from place to place, in a direction, fast or slowly; going uphill is harder than on the flat.
  6. ToolsReadyEvery tool is made for a job; some are very simple and some are complicated, and any tool can be made better.
  7. Ways of getting aroundReadyPeople travel by land, water and air; vehicles have changed from carts to cars, and some keep the air cleaner than others.
  8. Wheel and axleReadyA wheel and axle is a big wheel fixed to a thin rod, the axle, so that both turn together. Turning the big wheel takes a small force, and the thin axle turns with a big force. A doorknob, a tap, a screwdriver's fat handle, a steering wheel and the handle that winds up a well's rope are all wheels and axles.
  9. Balanced forcesLockedWhen two equal forces push or pull a thing in opposite directions, they cancel and nothing about its motion changes: the forces are balanced. Forces in the same direction add up. What is left when all the forces are added together is the net force, and a thing at rest starts moving only when the net force is not zero, in the direction of the bigger force. In a tug of war the rope stays still while the teams pull equally, and moves towards the stronger team.Opens after: Force
  10. CompassLockedA compass is a small magnet, a light needle that can turn freely. Wherever you are on Earth, it turns until one end points north and the other south. The end that points north is the magnet's north pole. With it you can find north, south, east and west, even on a cloudy night or at sea.Opens after: Magnets
  11. Contact and non-contact forcesLockedMost forces act only while two things touch: a foot kicking a ball, a hand opening a door, friction between a box and the floor. These are contact forces. Some forces act across a gap, without touching: the Earth's gravity pulls a falling apple, a magnet pulls a paperclip, and a rubbed plastic comb pulls bits of paper with an electric force. Non-contact forces are still forces between two objects, and they can act through paper, glass and water.Opens after: Force, Magnets
  12. GravityLockedThe Earth pulls everything towards it, without touching it. That pull is gravity. It is why a dropped ball falls, why rivers run downhill and why we don't float away. How hard the Earth pulls on a thing is that thing's weight.Opens after: Force
  13. Inclined planeLockedAn inclined plane is a slope, like a ramp or a plank leading up into a truck. Pushing a load up a slope takes a smaller force than lifting it straight up, but the load travels a longer way. The gentler the slope, the smaller the push and the longer the path. Ramps, roads that zigzag up a mountain and slides are inclined planes.Opens after: Force
  14. LeversLockedA lever is a bar that turns on one point, called the pivot. Pushing on the bar far from the pivot lets a small push lift a big load near it. See-saws, bottle openers, scissors and wheelbarrows are all levers.Opens after: Force
  15. PulleyLockedA pulley is a wheel with a groove round its edge that a rope runs in. With one pulley fixed at the top, you pull down on the rope and the load goes up: the pulley changes the direction of your pull, so you can lift with your whole body's weight. Pulleys raise flags, curtains and buckets from wells. Builders and cranes use several pulleys together, which lets a smaller pull lift a heavy load.Opens after: Force
  16. Slippery and roughLockedThings slide easily on smooth, icy ground and hardly at all on rough ground: that rubbing is called friction.Opens after: Things that move
  17. VelocityLockedHow fast and in which direction position changes - distance per unit time, with a direction.Opens after: Position
  18. AccelerationLockedHow quickly velocity changes - speeding up, slowing down or turning.Opens after: Velocity
  19. Air resistanceLockedAir is made of tiny particles, and anything moving through it has to push them aside. The air pushes back, against the motion: that force is air resistance. It grows with speed, and with how wide the thing is: a flat sheet of paper drifts down slowly, while the same sheet crumpled into a ball falls fast. So fast cars, trains and planes are built long and narrow at the front, and racing cyclists bend low, while a parachute is made wide to catch as much air as it can and slow the fall.Opens after: Slippery and rough
  20. Newton's first lawLockedAn object keeps its velocity - stays at rest or keeps moving in a straight line - unless a net force acts on it.Opens after: Force, Velocity, Balanced forces
  21. ScrewLockedA screw is a rod with a slope wound round it in a spiral, called the thread. Each full turn drives the screw a little way in, so a small turn of the hand pulls it in with a big force and holds things together very firmly. Wind a paper triangle round a pencil and its sloping edge makes the same spiral. Bottle caps, jar lids and bolts hold on with threads too.Opens after: Inclined plane
  22. WedgeLockedA wedge is a tool with a thick back and a thin, sharp edge, like two slopes back to back. Pushing on the back drives the thin edge in, and its sloping sides push things apart with a big force. So a wedge cuts, splits and digs, where a ramp is for moving loads. Knives, axes, chisels, the point of a nail, a pickaxe and our front teeth all work as wedges.Opens after: Inclined plane
  23. How planes flyLockedAir that moves faster presses with less pressure. A plane's wing is shaped, curved on top and tilted up a little, so that air flows faster over it than under it. The air below then presses harder than the air above and pushes the wing up: that upward force is lift. Lift grows with speed, which is why a plane races along the runway before it can rise. Four forces act on a flying plane: its weight pulls it down, lift pushes it up, the engines' thrust drives it forward, and air resistance holds it back.Opens after: Air resistance, Gravity
  24. Newton's second lawLockedNet force equals mass times acceleration (F = ma) - the bigger the force, the bigger the change in motion; the bigger the mass, the smaller.Opens after: Newton's first law, Acceleration
  25. Simple machinesLockedSimple machines are six basic tools that make work easier: the lever, the inclined plane, the wedge, the screw, the pulley and the wheel and axle. They help by letting a smaller force do a job, or by changing which way you push or pull. Most machines around us are made of several simple machines working together: a pair of scissors is two levers whose blades are wedges, and a bicycle has wheels and axles, levers and screws.Opens after: Levers, Inclined plane, Wedge, Screw, Pulley, Wheel and axle

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