What is energy? In this section...

Transcription

1 What is energy? Energy is the power or ability to do work. It makes things change, it does things for us. Everything we do is connected to energy in one form or another. Inside our bodies energy makes us grow, move about, think and keeps us warm. In the world around us, energy gives us light and heat in our homes, it powers our machines and runs our cars. You cannot make energy and you cannot get rid of it, you can only change it into another type of energy. Over the years, people have learnt how to change energy from one form to another. This has helped to make our lives more comfortable and easy. In this section......we look at the many different forms of energy: light, heat, sound, movement (kinetic), electrical, chemical, elastic and gravitational.

2 ENERGY FROM THE SUN 1 The sun was our first source of energy, providing heat and light energy. Although there are other sources of energy today the sun is still Earth s primary source of energy. For the first humans (before they discovered fire) the sun was the only source of heat and light. When the sun went down at night, it became dark but cold. But the sun s energy is useful for much more than just light and heat. The energy from the sun is used by green plants. Plants capture the energy from the sun and change it into sugar, which is stored in their roots and leaves. The sugar provides energy for the plants to grow. This stored energy in plants is also useful to other living things. When animals and people eat plants, they get the energy stored in the plants. Animals and people then use this stored energy to keep them warm, grow, move and reproduce. photosynthesis Plants make food using the energy from the sunlight by a special process called photo (meaning light) synthesis (meaning making something). Photosynthesis means using light to make food. This can only happen when there is a chemical called chlorophyll present in the plant. Chlorophyll in the leaves gives plants their green colour. Chlorophyll uses light from the sun to change water, from the soil and carbon dioxide from the air into sugar (food) to provide energy for them to grow. Plants are like sugar factories, making and storing sugar in their cells. Sugar is the energy store in the plant. Plants also produce oxygen, which humans need to breath.

3 FOOD CHAINS 2 Food is the fuel that makes animals and our bodies work. Some of the food fuel gives us energy, some keeps us warm and some allows us to grow. Animals and people cannot change light energy into sugar like plants do, so they eat plants to get energy. The stored sugar in the plant is passed on to animals and humans. The food we eat provides us with energy. Almost every living thing depends on plants for its food supply. Even meat-eating animals feed on the plants that their prey have eaten. When living things feed on other living things, food chains develop - food or stored energy is moved from one living thing to another. A food chain always starts with a green plant. Many types of animals eat more than one type of food they might eat different types of plants, or several different animals. This means that many different food chains overlap and link. Linked food chains are called food webs. If one part of the food chain changes, it can affect the whole food web. food chain facts Green plants are called the producers in a food chain because they produce food for the rest of the chain. Animals and people who eat (or consume) plants are called the consumers. The food chain links the producers to the consumers. If one part of the food chain changes, it all changes. Animals that eat plants are called herbivores; animals that eat others animals are called carnivores; animals that eat both are called omnivores.

4 TYPES OF ENERGY 3 Energy cannot be made or lost but it can be transferred, or stored. It is easier to think about energy changing from one form to another, this is called transformation. Energy makes everything happen and can be divided into two types stored energy (called potential energy) and moving energy (called kinetic energy). In each of these groups there are a number of different forms of energy: Light Sound Heat Chemical Electrical Movement Gravitational Elastic energy facts Energy is measured in joules one unit of energy equals one joule. The term joule was named after the scientist James Prescott Joule. Electricity is measured in units of power called watts. The watt was named in honour of James Watt, the inventor of the steam engine.

5 LIGHT & SOUND ENERGY 4 LIGHT ENERGY We cannot see anything without light. Most of our light during the day comes from the sun. At night we get light when it is reflected off the moon. We also get light from many other sources: from fires, candles, lamps and light bulbs. light energy facts Light travels in straight lines called rays. If an object blocks the rays, a shadow forms because rays cannot bend round an object. Shadows have the same shape as the object. Sun rays travel at an amazing speed - over 186,000 miles per second! SOUND ENERGY Sound energy is made of vibrations that can travel through solids, liquids, air and gases. Sound vibrations would not be heard if we didn t have ears. The vibrations pass into our ears and are funnelled to our ear drum. The ear drum vibrates, moving tiny bones in the middle ear, which then vibrate into liquid in the ear. Hairs inside the liquid then send electrical impulses to the brain to register sound. sound energy facts Sound is measured in decibels. The level of the loudness depends on the size of the decibels. A rocket launch could be 180 decibels, whereas a whisper could be as quiet as 30 decibels. As sound vibrations spread, they begin to fade. The nearer you are to the source of the sound, the louder it is. If vibrations follow each other slowly, the sound they make is lower. We call this low pitch. If the vibrations are quick in succession they produce a high pitched sound. Some animals can hear sounds that are so high, or so low-pitched, that humans cannot hear them.

6 HEAT & CHEMICAL ENERGY 5 HEAT ENERGY Heat is vital to many living creatures, including people it keeps us warm (so that our bodies can work properly) and as humans we also use heat to cook food and heat water. Heat can come from the sun or from fires. Power stations can turn coal or oil into electricity that can be used to power machines that also produce heat. Some of the food we eat is changed into heat energy to warm our bodies from the inside. We are called warm-blooded. Other animals, such as snakes and lizards, need the heat from the sun to warm their bodies as they cannot change their food into heat. These animals are known as cold-blooded animals. When there is no sun, cold-blooded animals get cold and tend to remain still. heat energy facts Heat comes from molecules moving around. Heat travels through air and liquids in a circles - this is called convection. Heat moves through solids by conduction, where the molecules vibrate pushing and bumping the heat. Some materials let heat energy pass through them easily and are called conductors. An example of a conductor is metal. Some materials do not let heat pass through easily and these are called insulators. An example of an insulator is foam. CHEMICAL ENERGY Chemical energy is stored in food and in fuels, such as oil, coal and gas. Chemical energy is released from fuels when they are burnt. Energy is released from food when it is broken down inside our bodies. We use the chemical energy stored in food to make our bodies warm, to grow or to move. The energy released from burning oil, gas and coal is used to make machinery work or to power vehicles. Chemical energy can make something change into something else. The change is permanent and cannot be reversed. Think about baking a cake. Once the cake has been baked you cannot change it back into its original ingredients.

7 ELECTRICAL ENERGY 6 Electricity is a type of energy that comes from the movement of electrical charges. Everything around us is made up of atoms every planet, rock, tree, animal, the air we breathe, our water and even us! Atoms are very small particles made up of even smaller particles. The centre of the atom is called the nucleus (made up of protons and neutrons) and around the nucleus are electrons. A force can make these electrons move. Electricity is moving electrons. Lightning is electrical energy where the electrons move from one cloud to another or jump down to the ground. Static electricity is the shock you sometimes feel when you take your jumper off - it can make your hair stand on end. It is caused when the electrons jump from one object to another. electrical energy facts The Ancient Greeks discovered the first examples of static electricity when they found that amber behaved oddly by attracting feathers if it was rubbed against fur. In 1831, Michael Faraday discovered that electrical energy could be produced with magnets. Electrical energy can travel down cables at about 250,000 kilometres a second which is almost as fast as the speed of light!

8 MOVEMENT, GRAVITATIONAL & ELASTIC ENERGY 7 MOVEMENT ENERGY Movement or motion is when something is not still. Things cannot start or move on their own, they need force to get started (a pull or a push). A force can make things speed up, slow down, change direction or change shape. If two forces pull or push against one another, the bigger force wins. You cannot see these forces - just the effects of the force, for example, the movement of a ball being thrown, someone bouncing on a trampoline or a windmill s sails turning. ELASTIC ENERGY Elastic energy is when you stretch or twist something and it returns back to its original shape and size. You can see this type of energy with rubber or elastic bands or springs. GRAVITATIONAL ENERGY Gravity is a mysterious force. Everything in the universe attracts other things towards it the larger the thing, the more gravitational pull there is. The Earth is so huge that gravity pulls everything down to it. Without it everything would float around. Rain falling, dropping something or rolling a ball down a hill, jumping up high and landing back down again are all examples of Earth s gravity. It was in the late 1600 s that Sir Isaac Newton made all the important discoveries about movement and gravity.