Energy Flashcards: Physics Concepts and Formulas

Physics Symbols and Units

Every physics equation uses specific symbols and units - think of them as the language of physics. Once you master these, equations become much easier to understand.

Current (I) is measured in amps (A), whilst charge (Q) uses coulombs (C). Potential difference (V) gets measured in volts (V), and resistance (R) in ohms (Ω). For energy calculations, you'll need power (P) in watts (W) and energy (E) in joules (J).

Don't forget the mechanical quantities: mass $m$ in kilograms, height $h$ in metres, speed $v$ in metres per second, and gravitational field strength $g$ at 9.8 N/kg on Earth.

Quick Tip: Make flashcards with symbols on one side and units on the other - it's the fastest way to memorise them!

Energy Sources: Renewable vs Non-Renewable

Energy sources power everything from your gaming console to entire cities. There are two main categories: renewable and non-renewable sources.

Non-renewable sources like coal, oil, gas, and uranium will eventually run out. Fossil fuels are typically burned to create steam that turns turbines, generating electricity. They're reliable and cheap but produce harmful CO₂ emissions.

Renewable sources include wind, solar, hydroelectric, geothermal, tidal, and wave power. These won't run out and are environmentally friendly, but they can be unreliable - imagine trying to charge your phone when there's no wind!

Remember: Non-renewable = reliable but harmful; Renewable = clean but sometimes unreliable.

Comparing Energy Sources

The renewable vs non-renewable debate isn't just about running out of resources - it's about balancing reliability with environmental impact.

Renewable energy never runs out and produces no CO₂ during operation, making it brilliant for the environment. However, it can be unreliable - wind turbines need wind, solar panels need sunshine, and hydroelectric plants need flowing water.

Non-renewable energy is incredibly reliable, abundant, cheap, and versatile. You can fire up a coal plant whenever you need electricity. The downside? These sources will eventually run out and they're terrible for the environment, releasing CO₂ when burned.

Exam Tip: Questions often ask you to compare advantages and disadvantages - make sure you can list at least two for each type!

Energy Stores

Energy is like money - it can't be created or destroyed, only moved around between different energy stores. This is called the conservation of energy, and it's measured in joules (J).

Think of energy stores as different bank accounts where energy can be kept. Thermal energy is stored as heat, kinetic energy in moving objects, and gravitational potential energy in objects above ground level.

You'll also encounter elastic potential energy (in stretched springs), chemical energy (in batteries and food), magnetic energy, electrostatic energy, and nuclear energy. Each store has its own characteristics and uses.

Key Concept: Energy never disappears - it just moves from one store to another!

Kinetic Energy

Kinetic energy is the energy stored in moving objects - from a rolling football to a speeding car. If something's stationary, it has zero kinetic energy.

The formula is E = ½mv², where m is mass (kg) and v is speed (m/s). Notice how speed is squared - this means doubling the speed gives four times more kinetic energy!

You can rearrange this formula to find speed: v = √$2E/m$. This is super useful when you know the energy and mass but need to find how fast something's moving.

Pro Tip: Remember that v² means kinetic energy increases dramatically with speed - that's why car crashes at high speeds are so dangerous!

Gravitational Potential Energy

Gravitational potential energy (GPE) is stored in objects above Earth's surface - think of a book on a shelf or water behind a dam. The word "potential" means the energy could be released later.

The formula is E = mgh, where m is mass (kg), g is gravitational field strength (10 N/kg on Earth), and h is height $m$. The higher and heavier something is, the more GPE it has.

You can rearrange to find height: h = E/(mg). This is handy when you know how much energy something has and need to work out how high it is.

Real-world Connection: Hydroelectric power stations use GPE - water stored high up converts to kinetic energy as it falls, turning turbines!

Thermal Energy and Specific Heat Capacity

Thermal energy changes when objects heat up or cool down. The formula is E = mcΔθ, where Δθ (delta theta) represents the change in temperature.

Specific heat capacity $c$ tells you how much energy is needed to raise 1kg of a substance by 1°C. Different materials need different amounts of energy - water needs loads of energy to heat up, whilst metals heat up quickly.

When thermal energy increases, particles move faster and the temperature rises. To find specific heat capacity, rearrange the formula: c = E/(m × Δθ).

Everyday Example: This is why the sea stays warm longer than sand - water has a much higher specific heat capacity!

Elastic Potential Energy

Elastic potential energy is stored when you stretch, compress, or deform elastic objects like springs, rubber bands, or trampolines. The formula is E = ½ke², where k is the spring constant (N/m) and e is extension $m$.

Hooke's Law states that the force needed to stretch or compress a spring is proportional to the distance moved. Basically, the further you stretch it, the harder it gets to stretch further.

The spring constant tells you how stiff a spring is - a high value means it's hard to stretch, whilst a low value means it stretches easily.

Think About It: Bungee jumping, catapults, and even your mattress all use elastic potential energy!

Energy Transfers Between Stores

Energy transfers happen when objects interact within a system. For example, when a ball falls, gravitational potential energy transfers to kinetic energy.

In a closed system, no energy escapes to the surroundings, so total energy stays constant. At the top of a fall, you have maximum GPE and zero KE. At the bottom, you have zero GPE and maximum KE.

This means you can set GPE equal to KE: mgh = ½mv². This relationship is incredibly useful for solving problems about falling objects, rollercoasters, and pendulums.

Key Insight: Energy transfers explain everything from bouncing balls to hydroelectric power - master this concept and physics becomes much clearer!

Example Calculation: Rollercoaster Problem

Let's solve a classic physics problem: a 400kg rollercoaster drops 30m - what's its speed at the bottom?

First, calculate the GPE at the top: mgh = 400 × 10 × 30 = 120,000 J. In a closed system, this GPE converts entirely to KE at the bottom.

Using KE = ½mv², rearrange to get v = √$2E/m$ = √$2 × 120,000/400$ = 24.5 m/s.

There's a brilliant shortcut: since mgh = ½mv², the masses cancel out, giving you v = √(2gh) = √(2 × 10 × 30) = 24.5 m/s. This shortcut works for any falling object!

Exam Success: This type of calculation appears frequently in exams - practice the shortcut method to save time!