🔋 7th Grade Chapter 6 Understanding Energy:

Keywords: What is energy, types of energy, energy transfers, conservation of energy, energy sources,

🌟 6.1 What is Energy?

Energy is the ability to do work or cause change. It is what makes things move, light up, heat up, or even grow. Without energy, nothing would happen cars wouldn't move, lights wouldn't shine, and people couldn't run or think.

Energy is not a thing you can hold, but you can observe what it does.

For example:

• When you kick a ball, your muscles use energy.

• When a toaster heats bread, it uses electrical energy.

📘 Key Point: Energy is all around us and exists in many forms. It cannot be seen directly, but its effects are visible.

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⚡ 6.2 Types of Energy

There are many forms of energy, and each one does something different. Let’s explore the most important ones:

1.⚡ Kinetic Energy

Kinetic energy is the energy an object has because it is moving. The faster an object moves or the more massive it is the more kinetic energy it has.

🧮 Kinetic Energy Formula:

KE = (1/2) × m × v²

• KE = kinetic energy (in joules, J)
• m = mass of the object (in kilograms, kg)
• v = velocity or speed (in meters per second, m/s)

🧪 Example Calculation:

A soccer ball has a mass of 0.5 kg and is kicked at a speed of 10 m/s.
How much kinetic energy does it have?

KE = (1/2) × 0.5 × (10)² = 0.25 × 100 = 25 J

✅ The ball has 25 joules of kinetic energy.

🌍 Real-World Application: Car Safety

In car safety, understanding kinetic energy helps engineers design better braking systems and crash protection:

• A car moving at high speed has a lot of kinetic energy.
• When brakes are applied, this kinetic energy must be reduced to zero.
• Seatbelts, airbags, and crumple zones help absorb and safely transfer this energy during collisions.

👉 The greater the speed and mass of a car, the more energy must be managed in a stop or crash.

2. 🧲 Potential Energy

Potential energy is the energy that an object has because of its position, condition, or structure. It is called “potential” because it can be converted into other forms of energy, such as kinetic energy, under the right conditions.

Examples include:

• A rock at the edge of a cliff stores energy due to its height.
• A stretched rubber band stores energy because of its shape.
• Food stores chemical energy your body uses for movement and warmth.

📐 General Concept:

Potential Energy (PE) = m × g × h

• m: mass (kg)
• g: gravitational field strength (9.8 m/s² on Earth)
• h: height above ground (m)

🌍 A. Gravitational Potential Energy

This is the energy stored in an object because of its height above the ground. The higher and heavier the object, the more gravitational potential energy it has.

Examples:

• A book on a shelf
• A child at the top of a slide
• Water behind a dam

🧠 Key Idea: Gravitational potential energy increases with both height and mass.

📘 Read More: Gravitational Potential Energy – BYJU’s | HyperPhysics | Physics LibreTexts

⚗️ B. Chemical Potential Energy

This is the energy stored in the bonds of chemical substances. When these bonds are broken or rearranged in a chemical reaction, energy is released.

Examples:

• Food (your body breaks it down for energy)
• Fuels like gasoline or coal
• Batteries that power electronic devices

🧠 Key Idea: Chemical potential energy is released during chemical changes like digestion or combustion.

📘 Read More: Chemical Energy – Britannica Kids | What Is Chemical Energy? – ReAgent Science Blog | HyperPhysics: Chemical Energy

🧵 C. Elastic Potential Energy

This is the energy stored in **objects that can be stretched or compressed**, such as springs, trampolines, or rubber bands.

Examples:

• A stretched rubber band ready to snap
• A compressed spring in a toy or machine
• A bow drawn back with an arrow

🧠 Key Idea: The more an object is stretched or compressed, the more elastic potential energy it stores.

📘 Read More: Elastic Potential Energy – BYJU’s | What is Elastic Energy? – Solar Schools | Britannica Kids: Elastic Energy

3. 🔥 Thermal (Heat) Energy

Thermal energy is the energy produced by the movement of particles within matter. The faster the particles move, the more heat is generated, and the higher the temperature becomes.

For example, a hot cup of tea has more thermal energy than a cold one of the same size because its particles are moving more rapidly.

📐 Related Concept:

Q = mcΔT

• Q: heat energy (Joules)
• m: mass (kg)
• c: specific heat capacity
• ΔT: temperature change (°C)

📘 Learn more about thermal energy (BYJU’S)

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4. 💡 Light Energy

Light energy is a form of electromagnetic radiation that can travel through space. It is the only form of energy visible to the human eye. Common sources include the sun, lamps, and lasers.

Light energy is used in photosynthesis, solar panels, and fiber optic communication systems.

📐 Formula for Photon Energy:

E = h × f

• E: energy of a photon (Joules)
• h: Planck’s constant (6.626 × 10⁻³⁴ J·s)
• f: frequency of the light (Hz)

📘 Explore light energy at Solar Schools

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5. 🔊 Sound Energy

Sound energy is the energy carried by vibrating particles, usually through air, water, or solids. It originates from a source causing particles to move in waves.

We experience sound energy when we talk, clap, listen to music, or hear thunder. It is essential for communication and technology like sonar or ultrasound.

📐 Related Concept:

I = P / A

• I: intensity of sound (W/m²)
• P: power of the wave (Watts)
• A: area it spreads across (m²)

📘 Learn more about sound energy at Solar Schools

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6. ⚡ Electrical Energy

Electrical energy is produced by the movement of electric charges (usually electrons). It powers nearly everything in our daily lives, from household appliances to industrial machines.

Electricity is generated in power plants using turbines, solar panels, or batteries, and carried to homes and devices through power lines.

📐 Formula:

E = P × t

• E: electrical energy (Joules)
• P: power (Watts)
• t: time (seconds)

Learn more about electrical energy here

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🔄 6.3 Energy Transfers and Conversions

Energy can neither be created nor destroyed. It can only be transferred from one object to another or converted from one form to another. This fundamental concept is part of the Law of Conservation of Energy.

🔁 Energy Transfer

An energy transfer happens when energy moves from one object to another without changing its form. The type of energy stays the same, but it is passed along to a different object or location.

Example:

When a rolling ball hits another ball, some of its kinetic energy is transferred to the second ball. The second ball starts to move, while the first slows down. The energy remains kinetic; it simply shifts from one object to another.

📐 Related Formula:

In some cases, energy transfer is calculated using the formula for work:

Work Done (W) = Force (F) × Distance (d)

• W: energy transferred (in joules)
• F: force applied (in newtons)
• d: distance moved in direction of force (in meters)

🔄 Energy Conversion (Transformation)

An energy conversion (or transformation) occurs when energy changes from one form to another. This is how most machines and natural systems work by converting energy into a useful form.

Examples:

• A toaster converts electrical energy into heat energy to toast bread.
• A speaker converts electrical energy into sound energy.
• A bicycle generator converts kinetic energy into electrical energy.
• A fan converts electrical energy into kinetic energy and heat.

🎯 Activity Tip:

Look around your home or classroom. Try to identify different energy conversions happening around you. For example:

• A microwave converts electrical energy into microwave radiation and then into heat.
• A battery-powered toy car converts chemical energy into motion and sound.

📊 Visualizing Energy: Sankey Diagrams

To better understand how energy moves and changes form in a system, scientists and engineers use something called a Sankey diagram. These diagrams show the types of energy conversions taking place and how much energy is involved. The key feature of a Sankey diagram is that the width of each arrow represents the amount of energy being transferred or transformed. Larger arrows show more energy, while smaller ones show less. For example, in a light bulb, a wide arrow might show electrical energy entering the system, with a thinner arrow showing light energy output and another showing heat energy lost. Sankey diagrams help us visualize energy efficiency and identify where energy is wasted.

🔥 How Conventional Coal Energy Works

The electricity we use in our homes often begins as chemical potential energy stored in coal. This process of turning coal into electricity happens in several steps at a power station, and each phase involves an important energy transformation.

1. Pulverised Coal & Boiler (Chemical ➝ Thermal Energy)

Coal is crushed into a fine powder (called pulverised coal) to burn more efficiently. It is then fed into a boiler, where it is burned. This combustion process releases a large amount of heat energy.

2. Water Supply and Steam (Thermal ➝ Mechanical Energy)

Water is pumped into the boiler tubes surrounding the furnace. The heat from the burning coal turns this water into high-pressure steam. This is where thermal energy heats the water, changing it from liquid to gas.

3. Turbine (Steam Drives Movement)

The high-pressure steam flows into a turbine, causing it to spin. This is where thermal energy is converted into mechanical energy (kinetic energy) as the steam forces the blades to rotate.

4. Generator (Mechanical ➝ Electrical Energy)

The turbine is connected to a generator, which converts the turbine’s mechanical energy into electrical energy using electromagnetic induction.

5. Transformer & Transmission

The electricity produced is sent through a transformer, which increases the voltage so it can travel long distances efficiently through transmission lines.

6. Consumer Use

The electricity reaches our homes, schools, and businesses, where it powers everything from lights to computers. This is the final useful output of the entire energy conversion chain.

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♻️ 6.4 Conservation of Energy

One of the most important principles in science is the Law of Conservation of Energy. This law states that energy cannot be created or destroyed; it can only be transferred from one object to another or transformed from one form into another.

In other words, the total amount of energy in a system remains constant. It may change location or take on a new form, but it never disappears.

🎢 Example: A Child on a Swing

Imagine a child swinging back and forth on a playground. When someone pushes the swing, they are giving the child kinetic energy the energy of motion. As the child rises to the highest point, their kinetic energy is gradually converted into gravitational potential energy because of the height they reach. At the peak of the swing, the motion briefly stops, and most of the energy is stored as potential energy.

As the swing moves downward, that potential energy is converted back into kinetic energy. However, the swing doesn’t keep moving forever. Over time, it slows down and eventually stops.

Why? Because friction in the swing’s chains and air resistance work against the motion. These forces convert some of the mechanical energy into heat and sound. Gravity also plays a role, constantly pulling the swing back down and opposing its upward motion.

The energy isn’t gone it’s just been transformed into forms that are less obvious or more difficult to reuse.

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6.5 Energy Sources

🔌 What Powers Our World and at What Cost?

To power homes, schools, and cities, we rely on energy sources but not all are equal. Understanding where energy comes from, what elements we must mine, and how they affect the planet helps us make better choices for the future.

Energy sources fall into two major categories:

🔋 Non-Renewable Energy Sources

These sources take millions of years to form and cannot be replaced in a human lifetime. They are often cheap and widely used, but have serious environmental costs.

🪨 Coal

• Used for: Electricity generation
• Elements mined: Carbon (C), Sulfur (S), Arsenic (As), Mercury (Hg)
• Why it’s not sustainable: Mountaintop removal, CO₂ emissions, acid rain, water and air pollution

🛢️ Oil

• Used for: Fuel, plastics
• Mined resources: Hydrocarbons (C, H)
• Why it’s not sustainable: Oil spills, CO₂ emissions, drilling hazards

🔥 Natural Gas

• Used for: Heating, cooking, electricity
• Element: Methane (CH₄)
• Why it’s not sustainable: Fracking risks, methane leaks

⚛️ Nuclear Energy

• Used for: Large-scale electricity
• Mined elements: Uranium (U-235/U-238), Thorium (Th-232)
• Why it’s more sustainable than fossil fuels: No CO₂ emissions during operation, high energy yield
• Challenges: Waste management, finite uranium
• More info: China’s new thorium reactor

🌱 Renewable Energy Sources

These come from natural processes that are constantly replenished like sunlight, wind, and heat from the Earth. But even renewable energy has resource and mining impacts.

☀️ Solar Energy

• How it works: Photovoltaic (PV) cells convert sunlight into electricity
• Elements mined: Silicon (Si), Silver (Ag), Copper (Cu), Aluminum (Al), Tellurium (Te), Cadmium (Cd), Gallium (Ga)
• Challenges: Toxic chemical use, mining pollution

🌬️ Wind Energy

• How it works: Turbines convert wind motion into electricity
• Elements mined: Neodymium (Nd), Praseodymium (Pr), Dysprosium (Dy), Terbium (Tb), Iron (Fe), Boron (B), Copper (Cu)
• Challenges: Rare-earth mining pollution, wildlife disruption

💧 Hydropower

• How it works: Dams use moving water to spin turbines
• Materials: Steel, Copper, Concrete
• Challenges: Disrupted fish migration, sediment blockage

🌱 Biomass

• How it works: Burned organic material releases energy
• Materials: Wood, crops, manure
• Challenges: CO₂ emissions, land competition, deforestation

🌋 Geothermal Energy

• How it works: Heat from inside Earth generates steam
• Materials: Steel, Copper, Concrete
• Challenges: Seismic activity, location limitations

🌍 Summary Table

Source	Elements/Materials	Renewable?	Sustainable?	Key Issues
Coal	C, S, Hg, As	❌	❌	Pollution, habitat loss
Oil	Hydrocarbons (C, H)	❌	❌	CO₂, spills, drilling damage
Natural Gas	Methane (CH₄)	❌	⚠️	Methane leaks, fracking
Nuclear	Uranium (U), Thorium (Th)	❌	✅	Radioactive waste, long-term use
Solar	Si, Ag, Cu, Al, Te, Cd, Ga	✅	⚠️	Mining impacts, recycling needed
Wind	Nd, Pr, Dy, Tb, Fe, B, Cu	✅	⚠️	Rare earth mining, wildlife issues
Hydropower	Steel, Cu, Concrete	✅	⚠️	River disruption, habitat loss
Biomass	Organic matter	✅	⚠️	CO₂, land overuse
Geothermal	Steel, Cu, Concrete	✅	✅	Seismic risk, region-specific

💬 Reflection

Sustainability isn't just about choosing "green" energy it's about understanding the elements, mining practices, and ecological impact of how we generate power. Even renewable sources require mined materials. True sustainability means balancing our energy needs with the health of the planet.

Encourage students to explore: If you could design the ultimate clean energy source, what would it look like?

🧩 Final Thoughts

All energy systems depend on elements from the Earth. While renewable energy may replenish itself naturally, the materials used to capture and store it are finite and often involve environmental risks.

We must:

• Choose cleaner sources

• Mine responsibly

• Recycle rare materials

• Innovate new systems (like thorium nuclear)

🔗 Read more about China’s thorium reactor experiment

Understanding the chemistry of energy empowers students to become future engineers, scientists, and problem-solvers. Ask yourself: What energy solution would YOU invent if all the elements were in your hands?