Science Study Notes: Energy Changes

Hey there! Get ready to explore the amazing world of energy. Ever wondered how your phone works, how you can run, or how the sun keeps us warm? It's all about energy! In these notes, we'll learn what energy is, the different shapes it takes, and how it moves and changes all around us. It's a super important topic because energy is what makes everything happen! Let's get started.


1. What is Energy? The Power to Do Things!

In science, energy is simply the ability to do work or cause a change. It's not something you can hold, but you can see what it does. Think of it as a superpower that makes things move, get hot, or light up.

Different Forms of Energy

Energy comes in many different forms. Imagine you have a collection of different superhero action figures – they are all heroes, but they have different powers. Energy is like that! Here are the main forms you need to know:

  • Kinetic Energy: This is the energy of movement. Anything that is moving has kinetic energy.
    Examples: A running person, a moving car, a spinning fan.
  • Potential Energy: This is stored energy, waiting to be used. It's like a stretched rubber band – it's not moving, but it has the potential to!
    Examples: A book on a high shelf, a stretched elastic band, the water behind a dam.
  • Chemical Energy: This energy is stored in the bonds that hold atoms together. It's released during a chemical reaction.
    Examples: Food you eat, batteries, wood or coal before it's burned.
  • Thermal Energy (Heat Energy): This is the energy related to temperature. The hotter something is, the more thermal energy it has because its tiny particles are moving faster.
    Examples: A cup of hot chocolate, a bonfire, the heat from a light bulb.
  • Light Energy: This is the energy we can see. It travels in waves.
    Examples: Sunlight, light from a lamp, a phone screen.
  • Sound Energy: This energy is produced by vibrations that travel through the air (or other substances) to our ears.
    Examples: Talking, music from a speaker, a clapping sound.
  • Electrical Energy: This is the energy of moving electric charges (electrons), which we usually call electricity.
    Examples: The power from a wall socket, lightning.
How Do We Measure Energy?

We measure energy in units called joules (J). For larger amounts, we use kilojoules (kJ). You might also see the unit kilocalorie (kcal), which is often used to measure the energy in food (you probably know them as 'Calories').

Key Takeaway

Energy is the ability to cause change and it exists in many forms, like kinetic (moving), potential (stored), chemical, thermal (heat), light, sound, and electrical. We measure it in joules (J).


2. Energy Can Change! (Energy Conversion)

Energy is a master of disguise! It can change from one form to another. This is called energy conversion or energy transformation. This happens all the time. A single device can perform many energy conversions at once!

Let's look at a simple example: A battery-powered torch.

  1. The batteries have chemical energy stored inside them.
  2. When you switch the torch on, the chemical energy is converted into electrical energy, which flows through the wires.
  3. The electrical energy flows to the bulb, which converts it into light energy (the useful part!) and thermal energy (which is why the bulb gets warm).

So, the energy conversion is: Chemical → Electrical → Light + Thermal

Some Common Energy Conversions
  • Burning wood: Chemical energy in the wood is converted into thermal energy and light energy.
  • Photosynthesis: Plants are amazing energy converters! They take light energy from the sun and convert it into chemical energy, which they store as food.
  • Generating electricity: In a power plant, burning fuel (chemical energy) heats water to make steam. The steam's movement (kinetic energy) turns a turbine, which then generates electrical energy.
  • A person running: Chemical energy from food is converted into kinetic energy (for movement) and thermal energy (which is why you get hot when you exercise).
Key Takeaway

Energy doesn't stay in one form. It constantly changes from one type to another. This process, called energy conversion, is what makes our world work.


3. Energy is Never Lost! (The Law of Conservation of Energy)

This is one of the most important rules in all of science. The Law of Conservation of Energy states that:

Energy cannot be created or destroyed, it can only be converted from one form to another.

This means the total amount of energy in the universe is always the same! It just moves around and changes form.

Useful vs. Wasted Energy

When we use an appliance, we want it to convert energy into a useful form. For a lamp, useful energy is light. But no energy conversion is perfect. Some energy is always 'lost' or changed into a form we don't want. We often call this 'wasted' energy. Most of the time, this wasted energy is thermal energy (heat) or sound energy.

Example: A television.
Useful energy: Light and sound.
Wasted energy: Heat (you can feel the TV gets warm).

But remember, this 'wasted' energy isn't destroyed! It just makes the surroundings a little bit warmer. The total energy is still conserved.

Showing Energy Conservation: Sankey Diagrams

A Sankey diagram is a special type of flow chart that shows how energy is converted. The width of the arrows shows the amount of energy.

  • The arrow on the left shows the total energy input.
  • The straight arrow pointing right shows the useful energy output.
  • The arrows that curve away (usually down) show the wasted energy output.

Important: In a Sankey diagram, the width of the input arrow always equals the total width of all the output arrows added together. This is a visual way of showing that energy is conserved!

Key Takeaway

Energy is always conserved – it is never created or destroyed. In any energy conversion, the total energy you start with is the same as the total energy you end with, even if some of it is 'wasted' as heat or sound.


4. Getting the Most Out of Energy (Efficiency)

(This is an extension topic - great for challenging yourself!)

Some devices are better at their job than others. An 'energy-efficient' light bulb, for example, wastes very little energy as heat and turns most of the electrical energy into useful light.

Efficiency is a measure of how much of the input energy is converted into useful output energy. We usually give it as a percentage (%).

The formula to calculate efficiency is:

$$Efficiency = {Useful\;energy\;output \over Total\;energy\;input} \times 100\%$$

Example: Let's compare two light bulbs. Both use 100 J of electrical energy.

  • Old Filament Bulb: It produces 10 J of useful light energy. The other 90 J is wasted as heat.
    Efficiency = (10 J / 100 J) x 100% = 10% efficient.
  • Modern LED Bulb: It produces 85 J of useful light energy. Only 15 J is wasted as heat.
    Efficiency = (85 J / 100 J) x 100% = 85% efficient.

The LED bulb is much more efficient because it wastes less energy!

Key Takeaway

Efficiency tells us how good a device is at converting energy into its useful form. A more efficient device wastes less energy.


5. How Heat Moves Around (Heat Transfer)

Thermal energy (heat) always moves from a hotter place to a colder place. It can do this in three ways: conduction, convection, and radiation. Don't worry, we'll use simple examples to understand them!

1. Conduction

Conduction is how heat travels through solids. The heat energy is passed along from particle to particle, like a chain of people passing a bucket of water. The particles themselves don't travel, they just vibrate and bump into their neighbours, passing the energy along.

  • How it works: Direct contact of particles.
  • Best in: Solids, especially metals (which are good conductors).
  • Doesn't work in: A vacuum (empty space), because there are no particles to bump into each other.
  • Real-world example: If you put a metal spoon in a hot cup of tea, the handle will eventually get hot. Heat is conducted up the spoon. Materials that don't conduct heat well, like wood or plastic, are called insulators. That's why pot handles are often made of plastic!
2. Convection

Convection is how heat travels through fluids (liquids and gases). When a part of the fluid gets hot, it expands, becomes less dense, and rises. The cooler, denser fluid then sinks to take its place, gets heated, and rises too. This creates a circular movement called a convection current.

  • How it works: Movement of the heated fluid itself.
  • Best in: Liquids and gases.
  • Doesn't work in: Solids (particles can't move freely) or a vacuum.
  • Real-world example: Boiling water in a pot. The water at the bottom gets hot, rises, and the cooler water from the top sinks to get heated. Another example is a sea breeze, which is a giant convection current in the air.
3. Radiation

Radiation is how heat travels as waves (specifically, infrared waves). It does not need particles to travel, so it is the only way heat can travel through a vacuum (empty space).

  • How it works: Travels as waves, no particles needed.
  • Best in: A vacuum, but also works through transparent materials like air and glass.
  • Factors that affect it: Dark, dull surfaces are good at absorbing and emitting heat radiation. Light, shiny surfaces are poor at it (they reflect heat instead).
  • Real-world example: How we feel the heat from the Sun, even though it's millions of kilometres away across the vacuum of space. Another example is feeling the warmth of a campfire from a distance. This is why emergency blankets are shiny – to reflect your body heat back to you.
Did you know?

A vacuum flask (like a Thermos) is designed to stop all three types of heat transfer!
- The vacuum between the walls stops conduction and convection.
- The shiny silvered surfaces stop radiation.

Key Takeaway

Heat moves from hot to cold in three ways: conduction (through solids), convection (through liquids/gases), and radiation (through waves, even in a vacuum).


6. Where Do We Get Our Energy From? (Energy Sources)

We use a huge amount of energy every day. But where does it all come from? We call these places energy sources.

Fossil Fuels (The Non-Renewables)

Most of the world's energy today comes from fossil fuels. These are coal, oil, and natural gas. They were formed from the remains of ancient plants and animals millions of years ago.
They are called non-renewable because we are using them up much, much faster than they can be formed. Once they're gone, they're gone for a very long time!

Problems with Fossil Fuels:

  • Limited Supply: They will eventually run out.
  • Pollution: Burning them releases harmful gases into the atmosphere, which contributes to problems like acid rain and climate change.
Alternative Energy Sources (The Future of Energy)

Because of the problems with fossil fuels, we need to find other ways to get energy. These are called alternative energy sources. Most of them are renewable, which means they won't run out.

  • Solar Energy: Energy from the sun. We use solar panels to convert sunlight directly into electricity. It's clean, but doesn't work at night!
  • Wind Power: Uses wind turbines to convert the kinetic energy of the wind into electricity.
  • Hydroelectric Power: Uses the energy of moving water, usually from a dam, to turn turbines and generate electricity.
  • Biomass Energy: Energy from burning organic material, like wood or special crops. It's renewable because we can always grow more plants.
  • Nuclear Power: This source gets energy by splitting atoms (a process called fission). It produces a huge amount of energy from a small amount of fuel and doesn't cause air pollution. However, it is non-renewable and there are major concerns about the safe disposal of radioactive waste and the risk of accidents.
Concerns about Alternatives

Even renewable sources can have downsides. For example, some people worry that large wind farms (lots of wind turbines) can be noisy and harm birds. It's important to weigh the pros and cons of each energy source.

Saving Energy is the Best Source!

The cleanest and cheapest energy is the energy we don't use! Recognizing the need for saving energy is crucial. We can all help by making small changes in our daily lives:

  • Turn off lights when you leave a room.
  • Unplug electronics when you're not using them.
  • Walk or cycle for short journeys instead of using a car.
  • Use energy-efficient appliances.
Key Takeaway

Our main energy sources are non-renewable fossil fuels, which cause pollution and are running out. We are developing cleaner, renewable alternative sources like solar and wind. The most important thing we can all do is save energy.