Space Travel & Forces

Ever wondered how spacecraft actually move through the vacuum of space? It's all about Newton's third law - when rocket engines push gases out at high speed (action force), the gases push back on the rocket with equal force (reaction force), creating thrust.

Once in space, things get interesting because there's no friction or air resistance. When engines shut off, spacecraft keep moving at constant velocity forever - that's Newton's first law in action. To change direction or slow down, you need an unbalanced force.

Ion drives are brilliant for long-distance travel because they're incredibly fuel-efficient. They accelerate xenon ions and shoot them out at massive speeds, creating tiny but continuous thrust. Over months or years, this builds up incredible velocity. Gravitational catapults are another clever trick - spacecraft can "steal" kinetic energy from planets or moons by swinging around them, gaining speed without using any fuel.

Quick Tip: Remember F = ma - the same thrust will accelerate a lighter spacecraft much faster than a heavier one!

Vectors, Energy & Motion

Here's something that trips up loads of students: scalars only have size (like speed, distance, mass), whilst vectors have both size and direction (like velocity, displacement, acceleration). Think of it this way - saying "I'm going 30 mph" is speed, but "I'm going 30 mph north" is velocity.

Work is simply energy transfer, calculated as W = Fd. When you lift something, you're doing work against gravity and giving it gravitational potential energy $Ep = mgh$. Drop it, and that converts to kinetic energy $Ek = ½mv²$ as it speeds up.

Projectile motion might seem complex, but break it down: horizontal velocity stays constant (no forces acting sideways), whilst vertical velocity changes due to gravity pulling downward. Think of a football - it travels forward at steady speed whilst simultaneously falling faster and faster.

Light years measure the incredible distances in space - it's how far light travels in one year (about 9.5 × 10¹⁵ metres). That's roughly 6 trillion miles!

Memory Trick: Vectors have direction - think of arrows pointing somewhere. Scalars are just numbers with units.

Waves & Their Properties

Waves are everywhere - from the music in your earphones to the light hitting your eyes right now. Transverse waves (like light and water waves) vibrate perpendicular to their direction of travel, whilst longitudinal waves (like sound) vibrate parallel to their direction.

The key wave equation you'll use constantly is v = fλ $speed = frequency × wavelength$. Remember that amplitude measures how intense the wave is - bigger amplitude means louder sound or brighter light. Wavelength is the distance between identical points on consecutive waves.

Diffraction explains why you can hear someone calling from around a corner. Waves bend around obstacles, and longer wavelengths bend more than shorter ones. When waves pass through gaps similar to their wavelength, they spread out dramatically - this is why radio waves (long wavelength) can reach into valleys better than light waves (short wavelength).

The relationship between frequency and period is simple: T = 1/f. If a wave has 10 cycles per second (10 Hz), each cycle takes 0.1 seconds.

Real-world connection: Your mobile phone uses wave diffraction to work indoors - radio waves bend around buildings and through gaps!

Electromagnetic Spectrum & Optics

The electromagnetic spectrum is like nature's ultimate toolkit - all these waves travel at light speed $3 × 10⁸ m/s$ but have different properties. Radio waves have the longest wavelengths and lowest frequencies, perfect for long-distance communication. Microwaves heat your food by making water molecules vibrate. Infrared is heat radiation that night-vision cameras detect.

Visible light is just a tiny slice of the spectrum that our eyes evolved to detect. Ultraviolet from the sun gives you vitamin D but also sunburn. X-rays penetrate soft tissue but not bones (hence medical imaging), whilst gamma rays are so energetic they're used to kill cancer cells.

Reflection follows a simple rule: angle of incidence equals angle of reflection, both measured from the normal (an imaginary line perpendicular to the surface). Refraction occurs when light changes speed moving between materials - this bends the light unless it hits straight on $incident angle = 0°$.

Convex lenses converge light to a focus point (think magnifying glass), whilst concave lenses diverge light (making things look smaller). The focal length determines how powerful the lens is.

Exam tip: Always draw the normal as a dotted line perpendicular to surfaces when solving reflection and refraction problems!

Electricity & Circuits

Electric current is simply the flow of charge, measured in amperes (A). Think of it like water flow - voltage is the pressure pushing charges along, current is how much charge flows per second, and resistance opposes this flow. Ohm's law $V = IR$ connects all three.

Direct current (DC) flows one way constantly (like from batteries), whilst alternating current (AC) switches direction regularly. Mains electricity is AC at 50 Hz, meaning it switches direction 50 times per second. AC is easier to generate and transmit over long distances.

In series circuits, current is the same everywhere, but voltage splits across components. In parallel circuits, voltage is the same across each branch, but current splits. Most home circuits are parallel - that's why one bulb blowing doesn't kill them all.

Electric fields exist around any charged object. Like charges repel, opposite charges attract - this creates forces that can accelerate particles and change their direction. Think of lightning - it's charges jumping through air when the electric field gets strong enough.

Safety note: Never connect a voltmeter directly to a power supply - it should always measure voltage across a component!

Space Objects & Satellites

Our universe contains an incredible variety of objects. Stars are massive balls of hot gas producing their own light and heat. Planets orbit stars and don't produce their own light. Moons are natural satellites orbiting planets, whilst asteroids are rocky chunks orbiting the sun.

Artificial satellites serve loads of purposes. Weather satellites track storms and help predict forecasts. GPS satellites (there are at least 24 of them) let your phone know exactly where you are. Communication satellites bounce TV, radio, and phone signals around the globe. Scientific satellites like the Hubble telescope observe distant galaxies.

Geostationary satellites are particularly clever - they orbit at exactly 36,000 km altitude with a 24-hour period, staying above the same spot on Earth's surface. Perfect for TV broadcasts and communications.

Space travel involves serious risks: massive fuel requirements, cosmic radiation that can cause cancer, explosive dangers during launch, and the challenge of re-entry. When spacecraft return to Earth, they slow down due to atmospheric friction - get the angle wrong and they'll bounce off the atmosphere like a stone skipping on water.

Fun fact: The delay you sometimes hear on satellite phone calls is the signal travelling 72,000 km (up to satellite and back down) at light speed!

Speed, Velocity & Acceleration

Speed is distance per unit time, but it can vary during a journey - that's why we calculate average speed using total distance ÷ total time. Instantaneous speed is how fast something's moving at one specific moment, like what your car's speedometer shows.

Acceleration is the rate of change of velocity $a = (v-u)/t$. Remember that acceleration can be negative (deceleration) when something slows down. The key equations for motion are d = vt for constant speed, and d = average speed × time when speed varies.

Light gates are brilliant for measuring instantaneous speed - they time how long it takes a small object to break the light beam. For acceleration experiments, you use two light gates separated by a known distance, measuring the speed at each point and the time between them.

Distance-time graphs tell the whole story: horizontal lines show stationary objects, diagonal lines show constant speed $steeper = faster$, and curved lines show acceleration or deceleration. The gradient at any point gives you the instantaneous speed.

Practical tip: When using light gates, make sure the object breaking the beam has a measurable width - you'll need this to calculate speed = width ÷ time.