OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~258 words · 1 min

Three rules that cover every motion Newton wrote these down in the 1680s. A dropped pencil and a launching rocket both obey all three. First law: things resist change A hockey puck glides for ages because ice gives it almost no friction to

Physics

Physics · L2 · Newton's Three Laws of Motion

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Note~157 words · 1 min

One path, or many? A circuit is a loop from the battery and back. How the parts sit in that loop decides everything. Series: a single chain Parallel: separate branches Your house is wired in parallel. Unplugging a lamp shouldn't kill the fr

Physics

Physics · L2 · Series & Parallel Circuits

@openstem

Note~255 words · 1 min

Light bends when it changes material Light travels straight through air. Cross into water or glass and it changes speed, and that speed change makes the ray bend. That's refraction. Lenses: refraction on purpose A lens is curved transparent

Physics

Physics · L2 · Refraction & Lenses

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Note~235 words · 1 min

Heat always flows hot to cold Wherever there's a temperature difference, heat moves until it evens out. There are exactly three routes. Conduction: particle to particle Metals conduct well because their electrons move freely. Wood and air c

Physics

Physics · L2 · Heat Transfer: Conduction, Convection, and Radiation

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Note~262 words · 1 min

Density is mass per unit of space Compare everything to water Water is about 1 g/cm³, which makes it a convenient yardstick. Ice floating is why lakes freeze from the top down, and why fish survive winter. Archimedes' principle The upward b

Physics

Physics · L2 · Density & Buoyancy

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Note~251 words · 1 min

Pressure is force divided by area Spot it around the house Atmospheric pressure On Everest each breath carries far less oxygen, which is why climbers carry bottles. Why ears pop Underwater

Physics

Physics · L2 · Pressure: Atmospheric & Fluid

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Note~274 words · 1 min

Current makes magnetism too Permanent magnets aren't the only source. Any current flowing in a wire creates a magnetic field around it. You can't see it, but a compass placed nearby will swing to line up with it. One straight wire gives a w

Physics

Physics · L2 · Magnetism & Electromagnets

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Note~206 words · 1 min

Work has a strict meaning here Everyday "work" means effort. Physics work means a force moved something along the direction of that force. Push with 10 N, move it 2 m: 20 joules of work. The part that catches people out No movement means no

Physics

Physics · L2 · Work & Power

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Note~211 words · 1 min

Momentum needs both mass and speed It measures how hard something is to stop. Comparing real objects A crawling truck beats a hurled tennis ball. Mass can outweigh a big speed difference. Collisions depend on the mass ratio Why crashes hurt

Physics

Physics · L2 · Momentum & Collisions

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Note~366 words · 2 min

Charge that stays put Atoms carry positive charge in the nucleus and negative charge in the electrons around it. Normally they balance, so things are neutral. Rub two surfaces together and electrons move from one to the other. One ends up w

Physics

Physics · L2 · Static Electricity

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Note~218 words · 1 min

Three things, one equation Know any two and you can find the third. Rearranged: I = V ÷ R, and R = V ÷ I. The pattern to hold onto With resistance fixed, more voltage means more current. Push harder, more flows. In the first three rows the

Physics

Physics · L2 · Introducing Ohm's Law

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Note~374 words · 2 min

Two independent questions Every sound starts with something vibrating: a string, a drum skin, your vocal cords, a speaker cone. That vibration pushes and pulls the air, sending squeezed and stretched regions outward to your ear. A hummingbi

Physics

Physics · L2 · Sound: Pitch, Loudness & Echoes

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Note~395 words · 2 min

One balance point Every object has a single point where all its weight seems to act from: the centre of mass. Support it exactly there and it balances, however oddly the weight is spread around. The rule for staying up The base of support i

Physics

Physics · L2 · Center of Mass & Stability

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Note~323 words · 2 min

Curve the surface, change the reflection A flat mirror bounces light back evenly, so your reflection is the same size and the right way up. Curve the surface and the rays get pulled together or pushed apart instead. Concave: curving inward

Physics

Physics · L2 · Curved Mirrors

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Note~325 words · 2 min

Motion that repeats Periodic motion is any motion that repeats the same pattern over and over. A swinging pendulum is the classic, but a bouncing ball, a rocking chair and a heartbeat all qualify. Note the cycle isn't over at the far side.

Physics

Physics · L2 · Pendulums & Periodic Motion

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Note~340 words · 2 min

Putting a number on "easier" Levers and pulleys don't create force from nothing. They change how much force you need and how far you must apply it. Mechanical advantage is the number describing that multiplication. Levers A lever pivots on

Physics

Physics · L2 · Mechanical Advantage: Levers & Pulleys

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Note~286 words · 1 min

Power is a rate Every device uses energy to do its job. Power measures how FAST it's being used, and it depends on both the current flowing and the voltage across the device. P in watts, I in amps, V in volts. One watt means one joule every

Physics

Physics · L2 · Electrical Power & Energy

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Note~278 words · 1 min

Why heat makes things bigger Almost every material takes up slightly more space when heated. Heating makes its particles vibrate or move more vigorously, which pushes their average spacing apart a little. Across billions of particles, that

Physics

Physics · L2 · Thermal Expansion

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Note~340 words · 2 min

Drawing something invisible A magnet's pull can't be seen, but its shape can be mapped with field lines: imaginary lines showing which way a tiny compass needle would point at each spot, and how strong the field is there. Sprinkle iron fili

Physics

Physics · L2 · Magnetic Field Lines & Earth's Magnetism

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Note~345 words · 2 min

Sound bounces, like light Sound is a wave, so it reflects off surfaces. Bounce it off something hard and flat, far enough away, and it comes back as a delayed copy: an echo. It's also why a room full of soft furniture sounds dead while an e

Physics

Physics · L2 · Echoes, Sound Reflection & Sonar

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Note~240 words · 1 min

Pull twice as hard, stretch twice as far Hooke's Law, and it holds for most springs as long as you don't overdo it. The spring constant is stiffness Measured in newtons per metre. Bigger k means you need more force per centimetre. Worked: k

Physics

Physics · L2 · Springs & Hooke's Law

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Note~79 words · 1 min

Oscillations you can change A mass on a spring, a pendulum, a sound wave: they all repeat on a regular cycle. The graph below is a sine wave. Move the sliders and watch what each one controls.

Physics

Physics · L3 · Seeing Oscillations

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Note~164 words · 1 min

The law, in numbers One newton is the force that accelerates 1 kg at 1 m/s², so N and kg·m/s² are literally the same unit. Rearranging for the unknown Worked values F is the NET force Real objects feel several forces at once. A sled has you

Physics

Physics · L3 · Newton's Second Law: Solving for Force, Mass, and Acceleration

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Note~238 words · 1 min

Constant speed can still be accelerating It points at the centre of the circle. Centripetal means centre-seeking. Centripetal force is a job, not a new force Something real always supplies it. Which real force depends on the situation. Work

Physics

Physics · L3 · Circular Motion & Centripetal Force

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Note~319 words · 2 min

Every mass pulls on every other mass Gravity isn't an Earth thing. Any two objects with mass attract each other, from two apples on a table to two galaxies. Inverse square: it fades fast The plot below is that exact shape. It's the same 1/r

Physics

Physics · L3 · Universal Gravitation & Orbits

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Note~206 words · 1 min

Momentum is a vector Conservation, and why it holds No net external force on the system means total momentum before equals total momentum after. Elastic, inelastic, perfectly inelastic Momentum is conserved in all three. Kinetic energy is w

Physics

Physics · L3 · Conservation of Momentum

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Note~169 words · 1 min

Kinetic energy, then the theorem The work-energy theorem ties that straight to work done: What the sign tells you Worked: pushing a cart from rest 2 kg cart, 10 N net force, 4 m of push. Final speed? Mass, force, distance. That's all it too

Physics

Physics · L3 · The Work-Energy Theorem

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Note~264 words · 1 min

Four numbers describe any repeating wave A 10 Hz wave cycles ten times a second, so its period is 0.1 s. Frequency and period are the same fact stated two ways. The wave speed equation It holds for any periodic wave: sound, light, water, a

Physics

Physics · L3 · Wave Properties: Wavelength, Frequency, and Speed

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Note~226 words · 1 min

Two ways to wire them, two different answers Real circuits rarely have one resistor. How you connect them changes the total resistance the battery sees, and therefore the current. Series: resistances add The same current has to fight throug

Physics

Physics · L3 · Resistor Circuits

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Note~285 words · 1 min

Reflection: one rule Angle of incidence equals angle of reflection, both measured from the NORMAL, not from the surface. Refractive index Snell's law Worked: air into water at 40°. Total internal reflection Going the other way, from dense t

Physics

Physics · L3 · Reflection, Refraction & Snell's Law

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