Newton's three laws describe how forces control motion, and momentum measures exactly how much "motion" a moving object carries.
🔬 Recap: Newton's three laws
1st Law: Inertia
Objects resist changes to their motion — an object at rest stays at rest, and an object in motion stays in motion, unless a force acts on it.
2nd Law: F = ma
Force equals mass times acceleration.
3rd Law: For every action, there is an equal and opposite reaction.
🏃 Momentum
Momentum measures how much motion an object has — it depends on both how heavy the object is and how fast it's moving.
p = m × v
mass = 5 kg, velocity = 4 m/s
p = 5 × 4 = 20 kg·m/s
🖼️ See it
a = F ÷ m: the same force gives half the acceleration to twice the mass.Pushing a wall pushes you back with an equal force, but the two forces act on different objects.
📝 Worked examples
Example 1 · Second law
A 5 kg cart is pushed with a net force of 15 N. What is its acceleration?
F = m × a → a = F ÷ m = 15 ÷ 5 = 3 m/s²
Example 2 · Weight
Weight is the force of gravity: W = m × g. With g = 10 m/s², a 6 kg bag weighs 60 N.
Example 3 · Momentum
p = m × v
2 kg × 4 m/s = 8 kg·m/s
1000 kg car at 20 m/s → 20 000 kg·m/s
📌 The three laws in one line each
Inertia: an object keeps its motion unless a net force acts on it.
F = ma: more force means more acceleration; more mass means less.
Action–reaction: every force has an equal and opposite force on a different object.
Action–reaction pairs act on different objects, so they never cancel each other out. When you push a wall, the wall pushes you back.
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Newton's first law
Newton's first law is also known as the law of:
Objects keep doing what they are doing unless a force acts.
✏️ Quick check · 2 of 10
The momentum formula
Momentum is calculated as:
A heavier or faster object is harder to stop.
✏️ Quick check · 3 of 10
Newton's third law
Newton's third law describes:
Push on a wall and the wall pushes back on you.
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An object has a mass of 5 kg and moves at 4 m/s.
What is its momentum, in kg·m/s?
Enter an exact answer, without rounding.
kg·m/s
p = m × v: 5 × 4.
✍️ Type your answer · 5 of 10
An object has a mass of 10 kg and moves at 3 m/s.
What is its momentum, in kg·m/s?
Enter an exact answer, without rounding.
kg·m/s
p = m × v: 10 × 3.
✍️ Type your answer · 6 of 10
Use F = ma. A 6 kg object accelerates at 2 m/s².
What force acts on it, in newtons?
Enter an exact answer, without rounding.
N
F = m × a: 6 × 2.
✏️ Quick check · 7 of 10
Inertia
A passenger lurches forward when a bus brakes suddenly. This is best explained by:
Which law talks about objects keeping their motion?
✏️ Quick check · 8 of 10
Action and reaction
A rocket pushes gas downward. What pushes the rocket upward?
Every force has a partner.
✍️ Type your answer · 9 of 10
A 4 kg object accelerates at 2.5 m/s².
What net force acts on it?
Enter an exact answer, without rounding.
N
F = m × a.
✍️ Type your answer · 10 of 10
A 3 kg ball moves at 6 m/s.
What is its momentum?
Enter an exact answer, without rounding.
kg·m/s
Multiply mass by velocity.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Which property of an object measures its resistance to changes in motion?
Question 2 of 5
A 20 N net force acts on a 5 kg object. What is the acceleration?
Question 3 of 5
What is the momentum of a 1000 kg car moving at 20 m/s?
Question 4 of 5
When a swimmer pushes the water backward, the water pushes the swimmer forward. This is:
Question 5 of 5
What is the weight of a 6 kg object on Earth (g = 10 m/s²)?
Lesson 2 · Forces
🎱 Elastic & Inelastic Collisions
Not all collisions behave the same way — some bounce cleanly apart while others crumple together, but one quantity stays the same either way.
💥 Elastic vs. inelastic collisions
In an elastic collision, kinetic energy is conserved — objects bounce apart without permanent deformation (like billiard balls). In an inelastic collision, kinetic energy is NOT conserved — some converts to heat, sound, or deformation, and objects may stick together (like a car crash).
Momentum, however, is always conserved in both types of collisions.
Elastic collision
Inelastic collision
elastic: objects bounce apartinelastic: objects stick together
📝 Worked examples
Example 1 · Perfectly inelastic collision
A 2 kg cart at 3 m/s hits a 1 kg cart at rest and they stick together.
Momentum before = 2×3 + 1×0 = 6 kg·m/s
Momentum after = (2 + 1) × v = 3v
3v = 6 → v = 2 m/s
Example 2 · Elastic collision
When two equal masses collide head-on elastically and one was at rest, they swap velocities, as with billiard balls: the moving ball stops and the other moves off at the same speed.
Example 3 · Direction matters
3 kg at +4 m/s and 2 kg at −1 m/s
Total momentum = 12 + (−2) = 10 kg·m/s
📌 What is conserved?
Quantity
Elastic
Inelastic
Momentum
Conserved
Conserved
Kinetic energy
Conserved
Not conserved (some becomes heat, sound, deformation)
Momentum is always conserved in an isolated collision, even when kinetic energy is not.
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Elastic collisions and energy
In an elastic collision, kinetic energy is:
Elastic collisions bounce perfectly, like snooker balls.
✏️ Quick check · 2 of 10
Inelastic collisions
In an inelastic collision, colliding objects often:
Think of two lumps of clay hitting each other.
✏️ Quick check · 3 of 10
Conservation of momentum
Momentum is conserved in:
With no outside force, total momentum never changes.
✍️ Type your answer · 4 of 10
Object A has momentum 12 kg·m/s and object B has momentum 8 kg·m/s, moving in the same direction. They collide and stick together (perfectly inelastic).
What is their total momentum after the collision, in kg·m/s?
Enter an exact answer, without rounding.
kg·m/s
Momentum is conserved: add 12 and 8.
✍️ Type your answer · 5 of 10
In an elastic collision, two objects have a combined kinetic energy of 50 J before colliding.
What is their combined kinetic energy after the collision, in joules (since KE is conserved in elastic collisions)?
Enter an exact answer, without rounding.
J
In an elastic collision, KE after equals KE before.
✍️ Type your answer · 6 of 10
Two objects have momenta of 15 kg·m/s and 5 kg·m/s moving in the same direction, and they collide and stick together.
What is the total momentum after the collision, in kg·m/s?
Enter an exact answer, without rounding.
kg·m/s
Momentum is conserved: add 15 and 5.
✏️ Quick check · 7 of 10
Always conserved
In every collision between two isolated objects, which quantity is conserved?
It is conserved whether the collision is elastic or not.
✏️ Quick check · 8 of 10
Elastic or inelastic?
A lump of clay hits a wall and sticks. This collision is:
Did the objects bounce apart?
✍️ Type your answer · 9 of 10
A 4 kg cart moving at 5 m/s sticks to a 6 kg cart at rest.
What is their speed afterwards?
Enter an exact answer, without rounding.
m/s
Total mass after is 10 kg.
✍️ Type your answer · 10 of 10
A 3 kg object moves at +4 m/s and a 2 kg object at −1 m/s.
What is the total momentum?
Enter an exact answer, without rounding.
kg·m/s
Treat the negative direction with a minus sign.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
In an elastic collision, which is conserved?
Question 2 of 5
Which collision is the best example of inelastic?
Question 3 of 5
A 2 kg cart at 3 m/s hits a 1 kg cart at rest, and they stick. What is the final speed?
Question 4 of 5
The total momentum after a collision, compared with before, is:
Question 5 of 5
A moving ball hits an identical stationary ball head-on, elastically. What happens to the first ball?
Lesson 3 · Fluids
💧 Density & Fluid Pressure
Fluids behave differently from solids, but two simple formulas — density and pressure — explain nearly everything about how they push and float.
📊 Density and fluid pressure
Density is calculated the same way you've seen before: mass ÷ volume.
Density = mass ÷ volume
Fluid pressure is calculated by dividing force by the area it acts on.
Fluid pressure = force ÷ area
💧 Pascal's principle and hydraulic lifts
Pascal's principle states that pressure applied to an enclosed fluid is transmitted equally in all directions. This is how hydraulic lifts work — a small force on a small piston creates the same pressure that produces a much larger force on a larger piston.
small piston, small forcelarge piston, large force
📝 Worked examples
Example 1 · Density
density = mass ÷ volume
200 g ÷ 50 cm³ = 4 g/cm³
Example 2 · Pressure on a surface
Pressure = force ÷ area. A 100 N box on a 0.5 m² base:
P = 100 ÷ 0.5 = 200 Pa (1 Pa = 1 N/m²)
Example 3 · Pressure in a fluid
P = ρ × g × h. Water has ρ = 1000 kg/m³. At 2 m depth (g = 10):
P = 1000 × 10 × 2 = 20 000 Pa
📌 Ideas to keep
The same force on a smaller area gives more pressure, which is why knives are sharp.
Fluid pressure increases with depth and with the density of the fluid.
Water: 1 g/cm³ = 1000 kg/m³.
Unit check: density in g/cm³ pairs with mass in g and volume in cm³. Do not mix in kg or m³ without converting.
✏️ Quick check · 1 of 10
The density formula
Density is calculated as:
Think of the unit g/cm³: mass per volume.
✏️ Quick check · 2 of 10
The fluid pressure formula
Fluid pressure is calculated as:
Think of the unit N/m²: force per area.
✏️ Quick check · 3 of 10
Pascal's principle
The hydraulic principle states that pressure applied to an enclosed fluid is:
In a closed fluid, a push in one place is felt everywhere.
✍️ Type your answer · 4 of 10
An object has a mass of 50 g and a volume of 10 cm³.
What is its density, in g/cm³?
Enter an exact answer, without rounding.
g/cm³
Density = mass ÷ volume: 50 ÷ 10.
✍️ Type your answer · 5 of 10
A force of 100 N is applied over an area of 4 m².
What is the pressure, in Pa?
Enter an exact answer, without rounding.
Pa
Pressure = force ÷ area: 100 ÷ 4.
✍️ Type your answer · 6 of 10
In a hydraulic lift, a small piston with area 2 m² has a pressure of 5 Pa applied. The large piston has an area of 10 m², and pressure is equal throughout the fluid.
What force does the large piston produce, in newtons? (force = pressure × area)
Enter an exact answer, without rounding.
N
Force = pressure × area: 5 × 10.
✏️ Quick check · 7 of 10
Sharp knife
Why does a sharp knife cut better than a blunt one?
Pressure = force ÷ area.
✏️ Quick check · 8 of 10
Pressure and depth
How does water pressure change as you dive deeper?
Think about the weight of water above you.
✍️ Type your answer · 9 of 10
A rock has a mass of 300 g and a volume of 100 cm³.
What is its density?
Enter an exact answer, without rounding.
g/cm³
Divide mass by volume.
✍️ Type your answer · 10 of 10
A 500 N force acts on an area of 2 m².
What is the pressure?
Enter an exact answer, without rounding.
Pa
Divide force by area.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
What is the mass of 5 cm³ of a material with density 2 g/cm³?
Question 2 of 5
What is the SI unit of pressure?
Question 3 of 5
Using P = ρgh with ρ = 1000, g = 10, h = 3 m, what is the pressure?
Question 4 of 5
Why do snowshoes stop you sinking into snow?
Question 5 of 5
A block has mass 600 g and volume 200 cm³. Is it denser than water (1 g/cm³)?
Lesson 4 · Fluids
⛵ Buoyancy: Archimedes' Principle
Whether something floats or sinks comes down to a simple contest between its weight and the buoyant force pushing back up on it.
💧 Archimedes' Principle
Archimedes' Principle states that the buoyant force on an object equals the weight of the fluid it displaces.
An object floats if the buoyant force is greater than or equal to its weight; it sinks if its weight is greater than the buoyant force. An object floats when its overall density is less than the fluid's density.
Floating
Sinking
📝 Worked examples
Example 1 · Buoyant force
Archimedes: the buoyant force equals the weight of the fluid displaced.
F_b = ρ_fluid × V_displaced × g
V = 0.002 m³ in water: 1000 × 0.002 × 10 = 20 N
Example 2 · Sink or float?
Wood 0.6 g/cm³ < water 1.0 → floats
Iron 7.9 g/cm³ > water 1.0 → sinks
Example 3 · Apparent weight
Weight in air = 30 N, buoyant force = 12 N
Apparent weight in water = 30 − 12 = 18 N
📌 Why do steel ships float?
A ship's hull is hollow, so its average density (steel + air) is less than water. It sinks until the water it displaces weighs the same as the ship.
A floating object: buoyant force = weight. The object only needs to displace enough water to match its own weight.
✏️ Quick check · 1 of 10
Define Archimedes' Principle
Archimedes' Principle states that buoyant force equals:
The upward push equals the weight of the water pushed aside.
✏️ Quick check · 2 of 10
Why objects float
An object floats when its density is:
Wood floats on water because it is less dense.
✏️ Quick check · 3 of 10
Why objects sink
An object sinks when:
If gravity pulls harder than the water pushes up, it goes down.
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An object weighs 20 N and displaces water weighing 25 N.
What is the buoyant force acting on it, in newtons?
Enter an exact answer, without rounding.
N
Buoyant force = weight of the fluid displaced.
✍️ Type your answer · 5 of 10
An object displaces 3000 cm³ of water. Water's density is 1 g/cm³.
What is the mass of the displaced water, in grams?
Enter an exact answer, without rounding.
g
Mass = density × volume: 1 × 3000.
✍️ Type your answer · 6 of 10
An object's weight and the buoyant force acting on it are both exactly 15 N.
By how many newtons do they differ?
Enter an exact answer, without rounding.
N
Take 15 from 15.
✏️ Quick check · 7 of 10
Float or sink?
An object has a density of 0.8 g/cm³. Placed in water, it will:
Compare with the density of water.
✏️ Quick check · 8 of 10
Archimedes' principle
The buoyant force on an object equals the:
Think about the displaced fluid.
✍️ Type your answer · 9 of 10
An object displaces 0.005 m³ of water (ρ = 1000 kg/m³, g = 10 m/s²).
What is the buoyant force?
Enter an exact answer, without rounding.
N
F = ρ × V × g.
✍️ Type your answer · 10 of 10
A stone weighs 30 N in air. In water, the buoyant force on it is 12 N.
What is its apparent weight in water?
Enter an exact answer, without rounding.
N
Subtract the buoyant force from the weight.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
A solid has density 1.5 g/cm³. In water it will:
Question 2 of 5
What is the buoyant force on 0.01 m³ of fully submerged object in water (ρ = 1000, g = 10)?
Question 3 of 5
For an object floating at rest, the buoyant force is:
Question 4 of 5
Why is it easier to lift a rock underwater?
Question 5 of 5
Which fluid gives the largest buoyant force on the same submerged object?
Lesson 5 · Energy
⚙️ Work, Power & Simple Machines
Work tells you how much energy you transferred, power tells you how fast you transferred it, and simple machines let you trade force for distance.
💪 Work and power
Work = force × distance
force = 20 N, distance = 5 m
Work = 20 × 5 = 100 J
Power = work ÷ time
Power is measured in watts (W) — how quickly work is done.
⚖️ The lever and mechanical advantage
A lever is a bar that pivots on a fulcrum. Pushing down on the long "effort arm" lifts a heavy load sitting on the short "load arm" — trading distance for force.
A longer effort arm needs less force to lift the same load.
Mechanical advantage = load ÷ effort
📝 Worked examples
Example 1 · Work
Work = force × distance moved in the direction of the force.
W = F × d = 10 N × 5 m = 50 J
Example 2 · Power
P = W ÷ t = 50 J ÷ 10 s = 5 W
Example 3 · Mechanical advantage
A lever lifts a 100 N load with a 25 N effort.
MA = load ÷ effort = 100 ÷ 25 = 4
📌 Machines trade force for distance
A ramp, lever or pulley makes a job easier (less force) but you must move through a longer distance. The total work is not reduced.
No movement, no work. Pushing hard on a wall that does not move does zero work, because d = 0.
✏️ Quick check · 1 of 10
The work formula
Work is calculated as:
Work is done when a force moves something a distance.
✏️ Quick check · 2 of 10
The power formula
Power is calculated as:
Power is how fast work is done.
✏️ Quick check · 3 of 10
The mechanical advantage formula
Mechanical advantage is calculated as:
How many times bigger is the load than your effort?
✍️ Type your answer · 4 of 10
A force of 20 N moves an object 5 m.
How much work is done, in joules?
Enter an exact answer, without rounding.
J
Work = force × distance: 20 × 5.
✍️ Type your answer · 5 of 10
100 J of work is done in 4 seconds.
What is the power, in watts?
Enter an exact answer, without rounding.
W
Power = work ÷ time: 100 ÷ 4.
✍️ Type your answer · 6 of 10
A machine lifts a 60 N load using only 20 N of effort.
What is its mechanical advantage?
Enter an exact answer, without rounding.
Mechanical advantage = load ÷ effort: 60 ÷ 20.
✏️ Quick check · 7 of 10
Zero work
You push a heavy wall as hard as you can, but it does not move. How much work do you do on the wall?
W = F × d.
✏️ Quick check · 8 of 10
Unit of power
What is the unit of power?
It is named after James Watt.
✍️ Type your answer · 9 of 10
A 20 N force pushes a box 3 m.
How much work is done?
Enter an exact answer, without rounding.
J
Multiply force by distance.
✍️ Type your answer · 10 of 10
A machine does 600 J of work in 20 s.
What is its power?
Enter an exact answer, without rounding.
W
Divide work by time.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
How much work lifts a 5 kg object 2 m (g = 10 m/s²)?
Question 2 of 5
A motor does 200 J of work in 4 s. What is its power?
Question 3 of 5
A load of 90 N is lifted with an effort of 30 N. What is the mechanical advantage?
Question 4 of 5
A ramp makes lifting a load easier, but you must:
Question 5 of 5
Which of these is NOT a simple machine?
Lesson 6 · Energy
⚡ Energy Transformations: GPE & KE
As objects move and change height, energy constantly transforms between two forms — and the total amount never changes.
mass = 2 kg, velocity = 6 m/s
KE = ½ × 2 × 6² = ½ × 2 × 36 = 36 J
The law of conservation of energy says total energy in a closed system stays constant, even as it converts between forms.
gravitational potential energykinetic energyas height drops, GPE converts into KE
📝 Worked examples
Example 1 · Gravitational potential energy
PE = m × g × h
2 kg at 5 m (g = 10): 2 × 10 × 5 = 100 J
Example 2 · Kinetic energy
KE = ½ × m × v²
4 kg at 3 m/s: ½ × 4 × 9 = 18 J
Example 3 · Conservation of energy
A 1 kg ball dropped from 5 m has PE = 50 J at the top. With no air resistance, all of it becomes KE at the bottom.
½ × 1 × v² = 50 → v² = 100 → v = 10 m/s
📌 Energy never disappears
Energy changes form but the total stays the same (conservation of energy). In real life some becomes heat from friction.
Battery fan: chemical → electrical → kinetic
Roller coaster: PE ⇄ KE as it climbs and falls
Speed squared! Doubling speed makes kinetic energy 4 times bigger, not 2 times. This is why high-speed crashes are far more dangerous.
✏️ Quick check · 1 of 10
The GPE formula
Gravitational potential energy is calculated as:
It depends on mass, gravity and height.
✏️ Quick check · 2 of 10
The KE formula
Kinetic energy is calculated as:
It depends on mass and speed, with speed squared.
✏️ Quick check · 3 of 10
Conservation of energy
In a closed system, total energy is:
Energy changes form, but the total stays the same.
✍️ Type your answer · 4 of 10
Use g = 10 m/s². A 4 kg object sits 5 m above the ground.
What is its GPE, in joules?
Enter an exact answer, without rounding.
J
GPE = m × g × h: 4 × 10 × 5.
✍️ Type your answer · 5 of 10
A 2 kg object moves at 6 m/s.
What is its KE, in joules?
Enter an exact answer, without rounding.
J
KE = ½ × m × v²: square 6 first.
✍️ Type your answer · 6 of 10
Use g = 10 m/s². A 10 kg object sits 3 m above the ground.
What is its GPE, in joules?
Enter an exact answer, without rounding.
J
GPE = m × g × h: 10 × 10 × 3.
✏️ Quick check · 7 of 10
Top of the swing
At the highest point of a swing, the child has the most:
Height means potential energy.
✏️ Quick check · 8 of 10
Energy chain
In a battery-powered toy car, which sequence is correct?
Start with where the energy is stored.
✍️ Type your answer · 9 of 10
A 3 kg object is lifted 4 m (g = 10 m/s²).
What is its gravitational potential energy?
Enter an exact answer, without rounding.
J
Multiply m, g and h.
✍️ Type your answer · 10 of 10
A 2 kg object moves at 6 m/s.
What is its kinetic energy?
Enter an exact answer, without rounding.
J
Square the speed first: 6² = 36.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
If an object's speed doubles, its kinetic energy:
Question 2 of 5
What is the PE of a 10 kg object at 2 m (g = 10)?
Question 3 of 5
What is the KE of a 0.5 kg ball moving at 4 m/s?
Question 4 of 5
As a ball falls, its energy changes from:
Question 5 of 5
With no friction, a roller coaster's total mechanical energy:
Lesson 7 · Waves
🌊 Wave Mechanics: Transverse, Longitudinal & the Wave Equation
Every wave you'll ever study is either transverse or longitudinal, and one simple equation connects a wave's speed, frequency, and wavelength.
🔋 Transverse vs. longitudinal waves
Transverse waves have particles moving perpendicular to the direction the wave travels (like light or a wave on a rope). Longitudinal waves have particles moving parallel to the wave's direction, forming compressions and rarefactions (like sound).
frequency = 50 Hz, wavelength = 4 m
speed = 50 × 4 = 200 m/s
Speed = frequency × wavelength, where frequency is measured in hertz (Hz) and wavelength in meters (m).
🌊 Mechanical vs. electromagnetic waves
Mechanical waves need a medium (like air, water, or a solid) to travel through — sound waves and water waves are both mechanical, and can't travel through empty space.
Electromagnetic waves don't need a medium and can travel through a vacuum — light and radio waves are both electromagnetic, which is how sunlight reaches us across empty space.
📝 Worked examples
Example 1 · The wave equation
Wave speed = frequency × wavelength.
v = f × λ
f = 5 Hz, λ = 2 m → v = 10 m/s
Example 2 · Period and frequency
T = 1 ÷ f
f = 5 Hz → T = 0.2 s
T = 0.5 s → f = 2 Hz
Example 3 · Transverse vs. longitudinal
Transverse waves shake at right angles to the direction of travel (light, water ripples). Longitudinal waves compress and stretch along the direction of travel (sound).
📌 Wave vocabulary
Wavelength (λ): distance from one crest to the next.
Frequency (f): waves passing per second, in hertz.
Amplitude: maximum displacement from rest. A bigger amplitude carries more energy.
Light needs no medium, so it travels through space. Sound is a mechanical wave and needs matter to travel through.
✏️ Quick check · 1 of 10
Transverse wave motion
In a transverse wave, particles move:
Think of a rope flicked up and down while the wave moves along it.
✏️ Quick check · 2 of 10
Longitudinal wave motion
In a longitudinal wave, particles move:
Think of a slinky pushed and pulled along its length.
✏️ Quick check · 3 of 10
The wave equation
The wave equation is:
Speed = how many waves per second × the length of each wave.
✍️ Type your answer · 4 of 10
Use v = f × λ. A wave has a frequency of 50 Hz and a wavelength of 4 m.
What is its speed, in m/s?
Enter an exact answer, without rounding.
m/s
v = f × λ: 50 × 4.
✍️ Type your answer · 5 of 10
Use v = f × λ. A wave has a frequency of 20 Hz and a wavelength of 3 m.
What is its speed, in m/s?
Enter an exact answer, without rounding.
m/s
v = f × λ: 20 × 3.
✍️ Type your answer · 6 of 10
Use v = f × λ, rearranged as λ = v ÷ f. A wave travels at 340 m/s with a frequency of 170 Hz.
What is its wavelength, in m?
Enter an exact answer, without rounding.
m
λ = v ÷ f: 340 ÷ 170.
✏️ Quick check · 7 of 10
Type of wave
Sound is what type of wave?
Sound is a pressure wave.
✏️ Quick check · 8 of 10
Bigger amplitude
A wave with a larger amplitude carries:
Think of a big ocean wave.
✍️ Type your answer · 9 of 10
A wave has a frequency of 4 Hz and a wavelength of 3 m.
What is its speed?
Enter an exact answer, without rounding.
m/s
Multiply frequency by wavelength.
✍️ Type your answer · 10 of 10
A wave has a period of 0.5 s.
What is its frequency?
Enter an exact answer, without rounding.
Hz
Frequency is 1 divided by the period.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
What is wavelength?
Question 2 of 5
A wave has f = 10 Hz and λ = 0.3 m. What is its speed?
Question 3 of 5
Higher frequency sound is heard as:
Question 4 of 5
Which wave can travel through a vacuum?
Question 5 of 5
What is the period of a 25 Hz wave?
Lesson 8 · Electricity & Magnetism
🧲 Magnetic Fields, Induction & Electromagnets
Magnetism and electricity are two sides of the same coin — a changing magnetic field can create electric current, and electric current can create a magnetic field.
⚡ Fields, induction & electromagnets
A magnet's field lines run from its North pole to its South pole.
Electromagnetic induction is when a changing magnetic field near a wire induces (creates) an electric current in that wire — this is how generators produce electricity.
An electromagnet is made by coiling wire around an iron core and running current through it; its strength increases with more coils, more current, or a stronger core material.
Electromagnet
Induction
coil of wireinduced current from moving magnet
📝 Worked examples
Example 1 · Poles
Like poles repel (N–N, S–S). Opposite poles attract (N–S). Field lines run from north to south outside the magnet.
Example 2 · Electromagnet
A current in a coil of wire makes a magnet. Make it stronger by adding more current, more turns of wire, or an iron core.
Example 3 · Transformer
Vₛ ÷ Vₚ = Nₛ ÷ Nₚ (secondary and primary turns).
Np = 100, Ns = 200, Vp = 10 V → Vs = 10 × 200 ÷ 100 = 20 V (step-up)
📌 Electromagnetic induction
A changing magnetic field through a coil induces a voltage. Move a magnet in and out of a coil and a current flows. This is how generators and transformers work.
Only change counts. A magnet sitting still inside a coil induces nothing. Transformers work only with alternating current (AC), because AC keeps the field changing.
✏️ Quick check · 1 of 9
Electromagnetic induction
Electromagnetic induction is:
Moving a magnet near a coil makes current flow.
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Making an electromagnet
An electromagnet is made by:
Current in a coil makes a magnetic field; iron makes it stronger.
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Electromagnet strength
Which of these does NOT increase an electromagnet's strength?
Which change would weaken it instead?
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An electromagnet's coil has 10 loops of wire. Doubling the number of loops makes it stronger.
If the number of loops is doubled, how many loops will there be?
Enter an exact answer, without rounding.
Double 10.
✍️ Type your answer · 5 of 9
An electromagnet uses 4 A of current. Tripling the current makes it stronger.
If the current is tripled, what is the new current, in amps?
Enter an exact answer, without rounding.
A
Multiply 4 by 3.
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Poles
What happens when two north poles are brought together?
Like repels like.
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Stronger electromagnet
Which change makes an electromagnet stronger?
More coils, more field.
✍️ Type your answer · 8 of 9
A transformer has 100 primary turns, 200 secondary turns and a primary voltage of 10 V.
What is the secondary voltage?
Enter an exact answer, without rounding.
V
Vs ÷ Vp = Ns ÷ Np.
✍️ Type your answer · 9 of 9
A step-down transformer: Np = 200, Ns = 50, Vp = 120 V.
What is Vs?
Enter an exact answer, without rounding.
V
Multiply Vp by Ns ÷ Np.
📝 Lesson quiz · 5 questions
0 / 5
Re-read the lesson, then give it another go.
Question 1 of 5
Outside a bar magnet, field lines point:
Question 2 of 5
A generator makes electricity by:
Question 3 of 5
Which does NOT strengthen an electromagnet?
Question 4 of 5
A compass needle points north because:
Question 5 of 5
Transformers work with:
Lesson 9 · Waves
📡 Analog vs. Digital Signals
Every signal that carries information — sound, video, data — is either analog or digital, and the difference shapes how well it survives being transmitted.
📡 Two kinds of signals
Analog signals vary continuously and smoothly, like a sound wave. Digital signals use discrete steps, represented in binary (combinations of 0s and 1s).
Digital signals are generally more resistant to noise and signal degradation than analog signals, which is why most modern electronics convert analog signals to digital ones (ADC = analog-to-digital conversion).
Analog signal
Digital signal
analog = smooth curvedigital = discrete steps
📝 Worked examples
Example 1 · Reading binary
Binary uses only 0 and 1. Place values are 1, 2, 4, 8, …