In this lesson, we learn about the concepts of work and energy. We start by defining work and its unit in the International System of Units (SI). We then explore how to calculate work done using the formula:
Work = force × distance moved in the direction of force.
Next, we define energy, along with its two main types: kinetic energy and potential energy, and we discuss their units. We’ll prove the formulas for kinetic energy (K.E. = ½ mv²) and potential energy (P.E. = mgh), and solve related problems.
We will also list different forms of energy, such as mechanical, thermal, and chemical, providing examples for each. Furthermore, we will describe how energy is converted from one form to another, focusing on sources like fossil fuels, hydroelectric power, solar energy, nuclear energy, geothermal energy, wind energy, and biomass energy.
Additionally, we will state the mass-energy equation (E = mc²) and apply it in problem-solving. We’ll also describe the electricity generation process, illustrating it with a block diagram that shows how fossil fuel input is transformed into electricity output.
Lastly, we will discuss the environmental issues related to power generation and explain energy flow through steady-state systems, such as a filament lamp, a power station, and a vehicle traveling at a constant speed on a level road.
ENERGY
Energy is a key concept in science that connects many natural phenomena. When we say an object has energy, we mean it can do work. For example, running water has the ability to turn water mills and turbines, demonstrating its energy.
Energy comes in various forms, including mechanical, heat, light, sound, electrical, chemical, and nuclear energy. It can change from one form to another. An object has energy if it can perform work. Mechanical energy is divided into two types: kinetic energy and potential energy.
Kinetic Energy
Kinetic energy is the energy of moving objects. For instance, moving air, or wind, can be harnessed to drive windmills or propel sailing boats. Similarly, flowing water in rivers can transport logs and generate electricity by turning turbines.
When an object is in motion, it has kinetic energy, which allows it to do work. If the object stops, it has used up all its kinetic energy. For example, consider an object with mass ( m ) moving at a velocity ( v ). If it travels a distance ( S ) but stops due to an opposing force, like friction, it can do work against that force until its kinetic energy is completely expended.
Potential Energy
Potential energy is the energy that an object has due to its position, even when it is at rest. For example, an apple hanging on a tree has the potential to do work when it falls, so it possesses potential energy.
Objects can have potential energy based on their position or condition. For instance, water stored at a height has potential energy because it can flow down and do work. Similarly, a hammer lifted to a certain height can do work when it falls, thanks to its gravitational potential energy.
Another example is a stretched bow, which has potential energy in its stretched position. When released, this energy propels the arrow forward; this type of energy is called elastic potential energy.
When a body of mass ( m ) is lifted to a height ( h ), it gains potential energy equal to the work done to lift it. Thus, potential energy depends on an object’s position or height.
FORMS OF ENERGY
Mechanical Energy
Mechanical energy is the energy an object has due to its motion or position. Examples include running water, wind, a moving car, a lifted hammer, a stretched bow, a catapult, and a compressed spring.
Heat Energy
Heat energy is produced by hot bodies and is released when fuels are burned. It is also generated when motion is resisted by friction. The food we consume provides us with heat energy, and the Sun is the primary source of heat energy on Earth.
Electrical Energy
Electrical energy is a widely used form of energy that can be easily transported through wires. We obtain electrical energy from batteries and electric generators, which are powered by sources like hydro, thermal, or nuclear energy.
Sound Energy
Sound energy is produced when objects vibrate, such as when you knock on a door or when musical instruments like drums or flutes are played.
Light Energy
Light energy is essential for visibility and is necessary for processes like photosynthesis in plants. We get light from sources such as candles, electric bulbs, fluorescent tubes, and mainly from the Sun.
Chemical Energy
Chemical energy is stored in food, fuels, and other substances. During chemical reactions, such as burning wood or coal, this energy is released as heat and light. Our bodies obtain energy from the food we eat, which is transformed into heat and muscular energy.
Nuclear Energy
Nuclear energy is released during nuclear reactions, including fission and fusion, as heat, light, and nuclear radiations. This energy is harnessed in nuclear reactors to generate electricity. The energy produced by the Sun for billions of years comes from these nuclear reactions occurring within it.