The seeds of dandelions are light and have a long feathery structure that allows them to fly. This structure helps them to be carried long distances by the wind. Wind Dispersal Seeds dispersed by the wind are usually light, small and have a feathery or wing-like structure. The seeds of the cotton plant are light and small. They have fine hair so that they can be carried away easily by wind. Seed Maple seeds have a wing-like structure that helps the seeds to flutter to the ground. With wind dispersal, the seeds are blown over a long distance and land in all kinds of places. Seed Explosive Mechanism Fruits dry up when ripe. They burst and shoot the seeds out of the fruits in different directions. This helps to scatter the seeds away from the parent plants. These are rubber seeds. Their fruits split open to disperse them. The pea pod splits open when it dries up causing the seeds to be thrown out. Balsam plants disperse their seeds by exploding, sending the seeds far away. 46 Hands-on Science Primary 5
Germination Seeds that have been dispersed will start to grow into young plants called seedlings. The growth of seeds into seedlings is the process known as germination. This process can only take place under the right conditions which are: • Presence of air • Presence of water • Presence of warmth Seeds will germinate if all three conditions above are fulfilled. Root Shoot Leaf The seedling will develop into an adult plant. The adult plant produces flowers. Once the flowers are pollinated, fertilization takes place. The life cycle of the plant repeats. There are similarities between fertilization in the sexual reproduction of flowering plants and humans. Do a simple presentation to your classmates by comparing the fertilization between flowering plants and humans in terms of the following: • What are the male and female parts? • Where are these parts located? • What are the reproductive cells in males and females? • How does fertilization take place? You may add on extra points other than the points listed above for a better comparison. Let’s Find Out! During germination, the roots grow first. Then, the shoot appears. At first, the seedling gets its food from its seed. When leaves are formed, the seedling starts making its own food with the presence of sunlight. Chapter 3 Reproduction 47
1. Label two jars as A and B. 2. Slightly wet a kitchen paper towel with water. Then put a small amount of water in the jar. 3. Put the damp kitchen paper towel in the jar. Make sure the paper towel touches the water. 4. Carefully push the seeds down into the paper towel around the edge of the jar so that they can be seen. 5. Repeat steps 2 to 4 so that you have two jars with kitchen towel and beans in each jar. 6. Place jar A near the window where sunlight can reach it. Place jar B in a dark cupboard where it is away from the sunlight. Make sure you refill some water in the jars every day. 7. Predict what happens to the seeds in both jars A and B. Write your prediction in the table below. Jar Prediction Observation A B 8. Observe any changes to the beans daily. Write your observation in the same table after five days. 9. Besides water, what do seeds need to germinate? 10. What is your conclusion from this activity? Let’s Try! Do seeds require light to germinate? • Green bean seeds • Kitchen paper towels • Two glass jars • Water Things needed: 48 Hands-on Science Primary 5
Reproduction in Non-flowering Plants Some plants such as ferns and mosses do not have flowers for reproduction. They are non-flowering plants. Therefore, they do not reproduce from seeds but reproduce from spores. Ferns produce spore bags on the underside of their leaves. When the spore bags dry out, the spores are released into the air. Then, they are dispersed by the wind to grow into new plants. The lifespan of ferns and mosses depends on the species. Some types of ferns can live up to 100 years whereas for mosses, it ranges from a couple to 10 years. Mosses tend to grow in moist and shady areas. They grow together in clumps. Mosses use spores to reproduce. They grow on the ground, rocks, soil, walls or on trees. They can grow on almost anything. Spore bag containing spores Moss Chapter 3 Reproduction 49
Fill in the blanks. Some words can be used more than once. 1. In human reproductive systems, testes produce while ovaries produce . 2. occurs when a sperm fuses with an ovum to form a fertilized egg in the female reproductive system. 3. and are the stages in human growth where the growth is rapid. 4. Boys grow faster than girls in the stage even though the growth occurs slowly. 5. Boys and girls experience changes in their body during . This is the stage that enables humans to reproduce. 6. The female frog lays its eggs directly into the water for fertilization to take place outside its body. This is called fertilization. 7. When the sperms of a male animal are released inside the female’s body to fertilize the egg, it is called fertilization. 8. In a flowering plant, the transfer of pollen grains from the anther to the stigma for fertilization is called . 9. In flowering plants, fertilization occurs in the . The ovary becomes the and the ovules become after fertilization. 10. Seeds are dispersed by , animals, and the explosive mechanism. 11. Germination is the growth of seeds into seedlings when , and warmth are present. 12. Non-flowering plants such as ferns and mosses reproduce through . puberty pollination adolescence fertilization wind childhood ova fruit infancy spores ovule external seeds water sperms internal air Let’s Scan 50 Hands-on Science Primary 5
Map It Out The stage during which adolescents reach sexual maturity and become capable of reproducing Puberty The growth of seeds into young plants in the presence of water, air and warmth Germination The transfer of pollen grains from the anther to the stigma of a flower Pollination The fusion of a sperm and an ovum to form a fertilized egg Fertilization Online QuickQuiz Explain It Reproduction Reproduction in humans Reproduction in animals Reproduction in plants • Reproductive systems • Fertilization and pregnancy • The growth of humans • Internal fertilization • External fertilization • Flowering palnts - Pollination - Fertilization - Seed dispersal - Germination • Non-flowering plants - Spores Chapter 3 Reproduction 51
Chapter 4 What do I know about energy and photosynthesis? 1. 2. 3. What do I want to know about energy and photosynthesis? 1. State that living things need energy to carry out life processes. 2. Recognize that the Sun is our primary source of energy. 3. Explain how humans and animals depend on plants as a source of food. 4. Explain photosynthesis and investigate its requirements. 5. Differentiate the ways in which plants and animals obtain energy. Energy and Photosynthesis A family is going on a picnic. They eat and have fun together. After the picnic, they clean up before they leave. How do they get the energy to do work? Humans need energy, but what about plants? Do they get energy the same way that humans do?
Living things need energy to carry out life processes. Where do you get energy from? What is the first thing in your mind when you are hungry? How do you feel if you have an empty stomach? Foods contain important nutrients that give us energy, help us grow, repair any damage in our cells and keep our body working well. Carbohydrates Vegetables Proteins Fruits We eat a variety of food from each food group to maintain a healthy diet. The healthy diet provides different nutrients to the body as well as provides us with the energy we need. 4.1 Energy from Food Energy and Chapter 4 Photosynthesis 53
Energy for Life Processes We get energy from food to carry out life processes. Digestion We use energy to eat and break down the food in our stomach. Then, the nutrients can be absorbed into the blood and used by our body. Respiration We need energy for breathing. The energy is used for the gaseous exchange between our body cells and the external environment. Growth and reproduction We need energy to grow as well as to repair old cells, develop and reproduce. 54 Hands-on Science Primary 5
Blood circulation Our body uses energy to carry blood that contains nutrients, oxygen and water to all body parts. At the same time, the blood also carries waste materials away from them. Living things obtain energy from their environment to carry out life processes. Our body also needs energy to remove waste products from the digestive process. The waste products are not usable and toxic. Movement We need energy to move. We need more energy when we do vigorous exercise and other physical activities. Energy and Chapter 4 Photosynthesis 55
Primary Source of Energy The energy is passed on from one animal to another animal. Humans and animals depend on plants as a source of food. The energy is passed on from the plants to the humans and animals. In this way, the Sun is our primary source of energy. The energy is passed on from the plants to the animals. We get energy from food. Where does food come from? We get energy from eating animals or plants. Plants get energy from the Sun to make food. The energy is passed on from the Sun to the plants. The Sun is our primary source of energy. It brings heat and light to our Earth. In the presence of light, green plants make their own food and produce oxygen for life on Earth. 56 Hands-on Science Primary 5
The energy from the Sun is passed on to plants when they make food. Let’s Think Based on this picture, list the examples of food we get from: (a) animals (b) plants The energy is passed on to animals when they eat plants. Energy and Chapter 4 Photosynthesis 57
Plants absorb light energy from the Sun. They use the light energy to make food through the process of photosynthesis. What do plants need to carry out photosynthesis? Sunlight Sunlight provides the plants with light energy. Carbon dioxide Plants take in carbon dioxide in the air through the openings in their leaves called stomata. Water The roots absorb water from the soil and transport it to the leaves. Chlorophyll It is a green pigment in leaves. It absorbs sunlight. The light energy enables plants to combine carbon dioxide and water to produce sugar. Sunlight Chlorophyll is found in the chloroplasts of plant cells. 4.2 Photosynthesis 58 Hands-on Science Primary 5
Oxygen Oxygen is produced. It is given out to the surroundings through the stomata. Sugar Sugar is produced. It is transported to all parts of the plant to be used as food. Excess sugar is stored in different parts of the plant as starch. What do plants produce after photosynthesis? The word equation for photosynthesis is as follows: Let’s Think Excess sugar is stored in different parts of the plant as starch. (a) Which are the parts of plants that store excess sugar? (b) Give an example of a plant for each of the parts you stated in (a). Take good care of plants. We need them for energy. Carbon dioxide + water sugar + oxygen in the presence of sunlight and chlorophyll Energy and Chapter 4 Photosynthesis 59
Work in pairs and differentiate the ways in which plants and animals: • obtain their food • obtain their energy You may do the comparison in a table and explain your points. Let’s Find Out! Let’s Try! Is sunlight necessary for photosynthesis? 1. Put two potted plants in the following conditions. Potted plant A: put in an open area exposed to sunlight Potted plant B: put in a shady area where sunlight cannot reach 2. Leave the plants for one week. 3. Pluck one leaf each from plants A and B to test for the presence of starch. 4. Your teacher will help you to remove the chlorophyll from the leaves of both plants respectively as follows. 5. Place the leaf on a white tile using forceps. Drop a few drops of iodine solution onto the leaf to test for starch. 6. Record your observations in the table below. • Two similar potted green plants • Beakers • Boiling tubes Things needed: • Alcohol • Bunsen burner • Tripod stands • Wire gauze • Water • White tiles • Iodine solution • Forceps Leaf Boiling water (a) Dip the leaf into a beaker of boiling water for five minutes to soften the leaf. Hot water Alcohol Bunsen burner (turned off) (b) Place the leaf into a boiling tube containing alcohol. Then, put the boiling tube into a beaker of hot water for five minutes to remove the chlorophyll. Hot water (c) Next, dip the leaf into a beaker of hot water for 15 seconds to remove alcohol from the leaf. Leaf Presence of sunlight Observation of the test for starch Remarks Potted plant A If the brown iodine solution turns blueblack, then starch is present. Potted plant B 60 Hands-on Science Primary 5
7. What do you need to observe in this activity? 8. In which plant is the starch present? 9. What is the relationship between the presence of starch and photosynthesis? 10. What is your conclusion from this activity? Let’s Try! Is water necessary for photosynthesis? 1. Expose two potted plants C and D to sunlight. 2. Water plant C every day. Leave plant D aside. 3. Pluck one leaf each from plants C and D after one week. 4. Test the leaves for the presence of starch. Refer to steps 4 and 5 of the previous activity. 5. Record your observations in the table below. Leaf Presence of water Observation of the test for starch Potted plant C Potted plant D 6. What variable is kept the same in this activity? 7. What variable is changed in this activity? 8. Is the activity a fair test? 9. In which plant is the starch present? 10. What is your conclusion from this activity? • Two similar potted green plants • Beakers • Boiling tubes Things needed: • Alcohol • Bunsen burner • Tripod stands • Wire gauze • Water • White tiles • Iodine solution • Forceps Energy and Chapter 4 Photosynthesis 61
Let’s Try! Is carbon dioxide necessary for photosynthesis? 1. Keep two potted plants E and F in a dark place for two days to remove the starch. 2. Then, set them up as shown below and keep in the sun for three hours. 3. Pluck one leaf each from plants E and F after three hours. 4. Test the leaves for the presence of starch. 5. Record your observations in the table below. Leaf Presence of carbon dioxide Observation of the test for starch Potted plant E Potted plant F 6. What variable is kept the same in this activity? 7. What variable is changed in this activity? 8. What do you need to observe? 9. In which plant is the starch present? 10. What is your conclusion from this activity? Things needed: • Two similar potted green plants • Beakers • Boiling tubes • Alcohol • Bunsen burner • Tripod stands • Wire gauze • Water • White tiles • Iodine solution • Forceps • Bell jars • Glass plates • Chemical which removes carbon dioxide Bell jar Chemical which removes carbon dioxide Glass plates Air without carbon dioxide Green plant Green plant F E Sunlight Air Sunlight 62 Hands-on Science Primary 5
Fill in the blanks. Some words can be used more than once. 1. All living things need to carry out life processes. 2. We get energy from to carry out life processes such as digestion, , growth, and movement. 3. Humans and animals depend on as a source of food to get energy. 4. The is our primary source of energy. 5. The Sun’s is passed on to us when we eat plants or animals. 6. Plants make food through the process of . 7. Green plants that have need carbon dioxide, and for photosynthesis. 8. Sugar and are produced during photosynthesis. 9. Sugar produced from photosynthesis can be changed to . 10. Excess sugar is stored as starch in the leaves, and other parts of the plant. respiration chlorophyll plants water reproduction energy roots photosynthesis starch Sun sunlight food oxygen Let’s Scan Energy and Chapter 4 Photosynthesis 63
The natural coloring matter that exists in plants and gives their leaves a particular color Map It Out A process where green plants use sunlight to make food Photosynthesis Pigment A green pigment found in the chloroplasts of plant cells that absorbs sunlight to make food Chlorophyll Online QuickQuiz Explain It Starch A white substance stored as food in different parts of the plant Energy and photosynthesis Energy from food Primary source of energy Photosynthesis To carry out life processes: • Digestion • Respiration • Blood circulation • Growth and reproduction • Movement • The energy from the Sun is passed on to plants. • When humans or animals eat the plants, the energy is passed on to them. Requirements to carry out the process: • Sunlight • Carbon dioxide • Water • Chlorophyll Products of the process: • Oxygen • Sugar 64 Hands-on Science Primary 5
Chapter 5 What do I know about electricity? 1. 2. 3. What do I want to know about electricity? 1. Describe a simple electric circuit, its components and their functions. 2. Recognize the difference between open and closed circuits, and the symbols used to represent the electrical components in a circuit diagram. 3. Explain the difference between series and parallel circuits. 4. Identify the factors that affect the brightness of bulbs in a circuit. 5. Identify electrical conductors and insulators, and their uses in our daily life. Electricity Light bulbs brighten up dark areas. They need electricity to work. The bulb in a flashlight needs electricity to light up. How does the bulb get electricity?
Batteries supply electricity for a torch to work. When electricity flows through the bulb, it lights up. The path along which the electricity flows is called an electric circuit. A simple electric circuit is made up of a battery, a connecting wire, a switch and a bulb. These are the components of the circuit. A torch is made up of these parts. When these parts are connected, electricity flows through the circuit and the torch lights up. The flow of electricity is called electric current. Electricity that moves from one place to another is called electric current. Electricity that gathers in one place is known as static electricity. This explains why a balloon sticks to us after we rub it against our clothes. Bulb Battery Switch Wire 5.1 Electric Circuits 66 Hands-on Science Primary 5
Parts of an Electric Circuit The basic parts of an electric circuit are shown below. • It is made of copper wires covered with a layer of plastic or rubber. • It connects the parts of the circuit together. • It allows electricity to flow through it. • It is a source of electricity. • It has two terminals. • At the positive terminal, there is a ‘+’ symbol. • At the negative terminal, there is a ‘–’ symbol. • It is used to break or complete an electric circuit. • If the switch is turned on, the electric current flows. • If the switch is turned off, the electric current stops flowing. • There is a tungsten filament in the bulb. • When electricity passes through it, it gives out light. Positive terminal Negative terminal Battery Bulb Tungsten filament Glass bulb Connecting wire Switch Chapter 5 Electricity 67
A switch is used to open or close a circuit. The circuit allows electric current to flow through it. • When the switch is on / closed, the bulb lights up. • Electric current flows through the circuit to light up the bulb. • The circuit is said to be a complete circuit or a closed circuit. • In a closed circuit, all of the parts are properly connected. • When the switch is off / open, the bulb will not light up. • This is because no electric current flows through the circuit. • The circuit is said to be an incomplete circuit or an open circuit. • In an open circuit, not all of the parts are properly connected. Let’s Try! How do we make an electric circuit that lights up a bulb? • Battery • Bulb • Connecting wire Things needed: 1. You are given a battery, a bulb and a connecting wire. 2. Join them together based on the diagrams given. A closed circuit An open circuit 5.2 Open and Closed Circuits 68 Hands-on Science Primary 5
3. Which circuits light up the bulb? Why? 4. What is your conclusion from this activity? Circuit Diagrams and Symbols A circuit diagram represents an actual circuit. It is a drawing that uses simple symbols to represent the different components in a circuit. A D B E C F Component Symbol Battery Connecting wire Bulb Switch Open switch Closed switch Chapter 5 Electricity 69
Circuit diagrams show us how the components of an electric circuit are connected. A closed circuit An open circuit Switch Bulb Battery Switch Bulb Battery A closed circuit diagram An open circuit diagram Let’s Try! How do we build simple circuits based on circuit diagrams? • Batteries • Battery holder • Bulbs Things needed: 1. You are given the things needed to build simple circuits. 2. Build simple circuits based on the circuit diagrams shown below. • Bulb holder • Switch • Connecting wires with crocodile clips A B C D 70 Hands-on Science Primary 5
3. Record your observations in the table below. Circuit Does the bulb light up? What is the corrective action to light up the bulb? A B C D 4. Why does the bulb light up when it is connected correctly to the battery? 5. What is your conclusion from this activity? Electric current flows through a closed circuit to light up a bulb. Bulbs can be arranged differently to build a series circuit or a parallel circuit. Series Circuit A series circuit is a closed circuit in which all the components are connected in a row, one after another to form a closed loop. The current flows in one path. Can you identify the current flow path in circuits A, B and C? Circuit A Circuit B 5.3 Series and Parallel Circuits Circuit A is made up of one bulb and one battery. Circuit B is made up of two bulbs, a closed switch and one battery. Chapter 5 Electricity 71
Circuit C Parallel Circuit A parallel circuit is a closed circuit in which the current flows in two or more paths. Can you identify the current flow path in circuits D, E and F ? Circuit D Circuit E Circuit F Circuit C is made up of two bulbs and three batteries. Circuit E is made up of two bulbs, a closed switch and one battery. Electric current flows in two paths. Circuit F is made up of three bulbs and two batteries. Electric current flows in three paths. Circuit D is made up of two bulbs and two batteries. Electric current flows in two paths. 72 Hands-on Science Primary 5
Factors Affecting the Brightness of a Bulb The brightness of a bulb in a circuit depends on the amount of electric current flowing through it. We can adjust the brightness of the bulb by making the following changes: • The number of batteries used • The number of bulbs used • The arrangement of bulbs Let’s Try! Will the brightness of the bulb be affected by the number of batteries used in a circuit? 1. Connect a battery to a bulb as shown in the circuit below. Switch on the circuit and observe the brightness of the bulb. Record your observation. 2. Switch off the circuit. Connect another battery to the existing battery side by side. Switch on the circuit again and record the brightness of the bulb. 3. Repeat step 2 by adding one more battery to the circuit. Record your observation. 4. Complete the table below to record the brightness of the bulb. Circuit Brightness of the bulb Circuit with one battery Circuit with two batteries Circuit with three batteries 5. How do we make the bulb brighter? 6. If we reduce the number of batteries, what happens to the brightness of the bulb? 7. What is your conclusion from this activity? Things needed: • Batteries • Battery holder • Bulbs • Bulb holder • Switch • Connecting wires with crocodile clips (These materials are also used for the activities on pages 74 and 75.) Chapter 5 Electricity 73
1. Connect a battery to a bulb and a switch to form a simple circuit. Switch on the circuit and observe the brightness of the bulb. Record your observation. 2. Switch off the circuit. Connect another bulb to the circuit as shown below. Switch on the circuit again and record the brightness of the bulbs. 3. Repeat step 2 by adding one more bulb to the circuit. Record your observation. 4. Complete the table below to record the brightness of the bulbs. Circuit Brightness of the bulbs Circuit with one bulb Circuit with two bulbs Circuit with three bulbs 5. Draw the circuit diagram for each of the circuits built. 6. How do we make the bulb dimmer? 7. If we reduce the number of bulbs, what happens to the brightness of the other bulbs? 8. What variable is kept the same in this activity? 9. What variable is changed in this activity? 10. What variable is responding in this activity? 11. What is your conclusion from this activity? Circuit with one bulb Circuit with two bulbs Circuit with three bulbs Let’s Try! Will the brightness of the bulb be affected by the number of bulbs used in a circuit? 74 Hands-on Science Primary 5
1. Build two circuits as shown below. 2. Switch on the circuits and observe the brightness of the bulbs of each circuit. 3. Compare the brightness of the bulbs and record your observations in the table below. Circuit Brightness of the bulbs A B 4. Draw the circuit diagrams for both circuits. 5. Which circuit has brighter bulbs? Why? 6. How should the bulbs be arranged in a circuit to give the brightest light? 7. Remove a bulb from circuit A. What happens to the other bulb? Why? 8. Remove a bulb from circuit B. What happens to the other bulb? Why? 9. What is your conclusion from this activity? Circuit A Circuit B Circuit A Circuit B Let’s Try! Will the brightness of the bulb be affected by the arrangement of bulbs in a circuit? Chapter 5 Electricity 75
A bulb in a circuit lights up brighter when more electricity flows through it. This can be done by adding more batteries to the circuit. BATTERY AA The bulb lights up brightly. BATTERY AA BATTERY AA The bulb becomes brighter. How do you make a bulb dimmer? A bulb in a circuit becomes dimmer if more bulbs are added to the circuit. BATTERY AA The bulb lights up brightly. BATTERY AA The bulbs are dimmer. There are two ways in which components of an electric circuit can be arranged. In a series circuit, there is only one path for the electricity to flow through the bulbs. If more bulbs are added, the brightness of the bulbs will decrease. If one bulb is removed or spoilt, the other bulbs do not light up because the circuit is incomplete. A series circuit A series circuit diagram In a parallel circuit, there are separate paths for electricity to flow through the bulbs. The electric current divides and flows through each of the three bulbs separately. If one bulb is removed or spoilt, the other bulbs will still light up. A parallel circuit A parallel circuit diagram 76 Hands-on Science Primary 5
Let’s Think Analyze the circuit diagram. What happens to the other bulbs if (a) bulb A is removed? (b) bulb B is removed? (c) bulb C is removed? B C A Find out the advantages and disadvantages of: • the series circuit • the parallel circuit Make the comparison in a table. Share your findings with your friends. Let’s Find Out! Materials that allow electricity to flow through them are electrical conductors, for example, metal keys, magnets, bolts and nuts. They can conduct electricity. Materials that do not allow electricity to flow through them are electrical insulators. Glass, plastic and cloth are examples of electrical insulators. They cannot conduct electricity. When they are connected to a circuit, the bulb does not light up. Electrical wires are made of copper that is a good conductor of electricity. Copper wires Plastic and rubber are insulators. They do not allow electricity to flow through them. A plastic or rubber covering is wrapped around electrical wires to protect us from electric shocks. Plastic or rubber insulators 5.4 Electrical Conductors and Insulators Chapter 5 Electricity 77
Water is a conductor. Watery substances such as orange juice and tomato juice can conduct electricity even though they are vegetables or fruits. Water Rubber is a more commonly used insulator. We are encouraged to wear rubber gloves and boots while working with electrical connections. Rubber Glass is a good insulator because it does not allow electricity to flow through it. Glass 78 Hands-on Science Primary 5
Let’s Try! What material can conduct electricity? Things needed: 1. Set up the apparatus as shown. 2. Connect a steel nail to the crocodile clips. Write down the material used to make the steel nail. 3. Observe whether the bulb lights up when it is connected to the steel nail. 4. Record your observation in the table below. Object Material used to make the object Does the bulb light up? Steel nail Coin Eraser Glass rod Wooden ruler Paper clip Straw Magnet Handkerchief 5. Repeat steps 2 and 3 with other objects listed in the table. Then, record your observations. 6. What can you infer if the bulb lights up? 7. Group the materials into electrical conductors and electrical insulators. Electrical conductor Electrical insulator 8. What is your conclusion from this activity? • Battery holder • Batteries • Connecting wires with crocodile clips • Bulb • Steel nail • Wooden ruler • Coin • Paper clip • Glass rod • Straw • Magnet • Handkerchief • Eraser Bulb Batteries Test object Crocodile clip Chapter 5 Electricity 79
Ways to Use Electricity Safely You have learned how to conserve electricity in Primary 1, can you recall what are the ways? Other than using electricity wisely, we must make sure that we use it safely. Do not connect too many plugs to a socket to reduce the risk of overloading and fire. Do not touch or use exposed electrical wires that may cause electric shocks. Hold the plastic handle when using electrical appliances. Plastic is an electrical insulator that protects us from direct contact with electricity. Switch off electrical appliances after use. Do not leave them on ‘standby’ mode. This is a way to conserve electricity. Do not touch electrical parts with wet hands. This is because water is a conductor that allows electricity to flow through it. 80 Hands-on Science Primary 5
Fill in the blanks. 1. An electric is the path through which electricity flows. 2. The components of an electric circuit are the battery, , bulb and connecting wire. 3. A circuit is a circuit through which electricity can flow through the components. 4. A bulb in an circuit does not light up. 5. A circuit diagram is a drawing that uses to represent the components in an actual circuit. 6. In a circuit, there is only one path for the electricity to flow. 7. In a circuit, there is more than one path for the electricity to flow. 8. A bulb will light up brighter if more are added to the circuit. 9. A bulb will light up dimmer if more are added to the circuit. 10. An electrical allows electricity to flow through it. 11. An electrical does not allow electricity to flow through it. 12. We must conserve electricity and use it . closed series parallel switch insulator batteries circuit conductor bulbs open safely symbols Let’s Scan Chapter 5 Electricity 81
Map It Out Electric circuits Open and closed circuits Electrical conductors and insulators Series and parallel circuits Electricity A closed circuit in which the current divides into two or more paths Parallel circuit Material that allows electric current to pass through it to conduct electricity Electrical conductor Material that does not allow electric current to pass through it to conduct electricity Electrical insulator Drawing that represents an actual electric circuit Circuit diagram Online Explain QuickQuiz It A closed circuit in which the electric current flows in one path Series circuit Components: • Bulb • Battery • Switch • Connecting wire An electric circuit can be represented using a circuit diagram. • Open circuit: electric current cannot flow through it • Closed circuit: electric current can flow through it and light up the bulb • Series circuit: electric current flows in one path • Parallel circuit: electric current divides into two or more paths • Factors affecting the brightness of a bulb: - the number of batteries used - the number of bulbs used - the arrangement of the bulbs • Electrical conductor: allows electricity to flow through it • Electrical insulator: does not allow electricity to flow through it 82 Hands-on Science Primary 5
Chapter 6 What do I know about simple machines? 1. 2. 3. What do I want to know about simple machines? 1. Identify the different types of simple machines. 2. Explain the functions of each type of simple machine. 3. Explain the precautionary measures in using simple machines. Simple Machines Children like to play in the playground. They play seesaw, slide, swing and others. These are simple machines. What are the other simple machines that you can find in your everyday life?
Did you know that we do work by using simple machines almost every day? We use a can opener to open a can of baked beans, a pair of scissors to cut a piece of paper and a ramp to move heavy boxes. These are some of the simple machines that we use every day. Look at the pictures below: A mother is carrying her groceries using a shopping trolley. A man is carrying his groceries using a box in his hands. Which of the above pictures shows an easy way to carry things with less effort? Simple machines are used to make our work easier. They allow us to complete our work with less effort and in a shorter amount of time. We can group simple machines into a few types based on their functions. The different types of simple machines are: • Lever • Pulley • Gears • Wheel and axle • Inclined plane • Screw • Wedge 6.1 Types of Simple Machines 84 Hands-on Science Primary 5
Levers A lever has three parts. The part where the lever is supported at one point is called the fulcrum. The part from the fulcrum to the weight we want to lift is called the weight arm. The part from the fulcrum to where we want to apply force, either pulling or pushing, is called the force arm. Let’s Try! Is it easier to lift a weight when the force arm is shorter, longer or the same as the weight arm? 1. Fold the toilet paper tube into a triangular shape. The tube will be the fulcrum. 2. Poke a hole in each of the paper cups using a sharp object. Make sure the holes are at the same height on each cup. 3. Insert both ends of the chopstick into each cup. The chopstick can rest on the tube and acts as a lever. 4. Position the fulcrum at the center. 5. Fix the position of the fulcrum with a thread. Then, put six bolts on one end of the lever as the weight. Paper cups Thread Chopstick Force Toilet paper tube in triangular shape Weight 6. Put some bolts at the other end as the force. Record the number of bolts needed to lift the weight of the six bolts. Position of the fulcrum At the center Shorter force arm Longer force arm Number of bolts needed to lift the weight 7. Adjust the chopstick on the tube to make the force arm shorter than the weight arm. 8. Repeat steps 5 and 6. 9. Repeat steps 5 and 6 with the force arm longer than the weight arm. 10. What is the factor that affects the results of the activity? 11. What is the best way to lift the weight with less force? 12. What is your conclusion from this activity? Things needed: • Toilet paper tube • Bolts • Two small paper cups • Chopstick • Thread Chapter 6 Simple Machines 85
When we push down one end of the lever, the other end will move upwards. Levers enable us to lift a heavy load with less effort. To use the least effort, the fulcrum should be placed as close as possible to the load. Large force Small force Effort Fulcrum Load E Effort L Load F Fulcrum L L F E E L F E L F E The positions of the effort, fulcrum and load are interchangeable. Based on their positions, we can group levers into first-class levers, second-class levers and third-class levers. First-class levers The fulcrum is located between the load and the effort. Examples of the levers are scissors, seesaws, pliers and crowbars. For first-class levers to work efficiently: • Place the fulcrum as near as possible to the load. • Apply the effort as far as possible from the fulcrum. A lever is simply a bar that rests and turns about a fixed point. It is useful for lifting or moving heavy things. The point at which the lever is resting is called the fulcrum. A force, known as effort, is applied at a point on the bar to lift a weight which is known as the load. 86 Hands-on Science Primary 5
F E L Second-class levers E E F L Third-class levers The load is located between the fulcrum and the effort. The effort is further from the fulcrum compared to the load. Examples of the levers are wheelbarrows, nutcrackers, and bottle openers. The effort is located between the load and the fulcrum. The load is further from the fulcrum compared to the effort. Examples of the levers are brooms, fishing rods and ice tongs. L E F E L F Chapter 6 Simple Machines 87
Pulley A pulley is a wheel with a groove. This groove is for a rope to move around the pulley. Pulleys are used to lift up or lower down objects. When we pull the rope, the wheel will turn. Thus, this will move the object that is attached to the other end of the rope. Pulleys help in lifting heavy things easily. Let’s take a look at the types of pulleys used in our daily lives: • Fixed pulleys • Movable pulleys • Pulley systems Fixed Pulley Fixed pulleys do not move. With a fixed pulley, the direction of force is changed. When the effort moves downwards, the load moves upwards. This type of pulley changes the direction of the force applied (effort). When we pull the rope downwards, the flag moves upwards. A fixed pulley is fixed at the flagpole. 88 Hands-on Science Primary 5
Movable Pulley Movable pulleys are not fixed to any support. They move together with the load. Movable pulleys do not change the direction of the force. Both the effort and load move in the same direction. This type of pulley reduces the force applied (effort). When the cable is pulled to move upwards, the load that attaches to the pulley will move upwards. Pulley System A pulley system consists of a fixed pulley and a movable pulley. It increases the force applied (effort) to produce a greater force to lift the load. A weightlifting machine in a gym works on a pulley system. We use the pulleys to help lift the weights. Pulleys make our work easier by: • changing the direction of a force • helping us to lift a load with less effort. The more pulleys are used, the lesser effort is needed. Chapter 6 Simple Machines 89
Gears A gear is a wheel with teeth around it. It is normally fitted with another gear. How do gears help us to do work? Gears are used to change the speed of the force applied. This depends on the size and the type of gear used. In most devices, the gears are fitted next to each other. When they join together, they turn together. When one gear in our watch turns, it causes the other gear to turn in the opposite direction. In this way, it changes the direction of the rotation. When the bigger gear turns in a clockwise direction, the smaller gear turns in an anticlockwise direction. The bigger gear turns slower with more force while the smaller gear turns more quickly with less force. Anticlockwise Clockwise 1 2 3 4 Let’s Think • Why does a bigger gear turn slower with more force compared to a smaller gear? • Gears are of different sizes. Which gear should be used for cycling uphill? Which gear should be used for racing bikes? Bicycles use gears to change the speed. The gears are connected by a chain. When the bicycle is pedaled, the chain transfers the force from the pedals to move the wheels to go around. The chain can be moved between gears of different sizes. 90 Hands-on Science Primary 5
Wheel and axle A wheel and axle is a simple machine that consists of a wheel which is connected to a rod called an axle. They are connected in such a way that they rotate together. A wheel and axle combination is a force magnifier. When a small force is applied to the wheel, it generates a larger force to move a load at the axle. This type of simple machine allows movement of larger objects over a distance with less force. Wheel Screwdriver Axle A man is fixing the door with a screwdriver. When he turns the wheel, the axle attached to it moves together. This simplifies work by rotating the screw into the door. An axle is a rod that runs through a hole in a wheel. When we ride a bicycle, the wheels spin in a balanced circle around an axle. Bicycles are made up of more than one type of simple machines! When we turn the wheel of the water tap, the axle connected to the wheel is turned together. This allows water to flow out of the tap. Wheel Axle Water tap A door knob is made up of a wheel fixed to a rod. When we gently turn the wheel, it releases the latch and the door is opened. Wheel Axle Doorknob Chapter 6 Simple Machines 91
Inclined Plane An inclined plane is a sloping surface. It is used to move a load from a lower spot to a higher spot more easily. It is also easier to push or pull a load up an inclined plane. Inclined planes have no moving parts. This type of simple machine reduces the force applied (effort) to move an object up to a higher spot over a greater distance. Some other examples of inclined planes are stairs, escalators and ramps (moving truck ramps). A slide allows the child to reach the lower spot faster and more easily without much effort needed. A ladder allows the man to easily reach a higher level to do repair work. Wheelchair ramp Wheelchair ramps allow wheelchair users to access a bus or a building more easily. 92 Hands-on Science Primary 5
Let’s Think Why do mountain roads go around the mountain? Screw A screw is a simple machine that is like an inclined plane. It is an inclined plane that wraps around a shaft. It can be driven into an object or flat surface using a screwdriver. When the screw is rotated, it moves downwards into the object following the screw thread (inclined plane). A screw needs to be rotated many times to drive it down a small distance. However, only a small effort is applied on the screw to produce a large downward force. Screw head These are the examples of screws. They can be used to fasten or hold things tightly together and to raise weights. A screw cap is used as an effective seal for bottles and jars. It is easily opened and closed by consumers. A corkscrew is screwed into the cork by rotating the handle and then pulling it out from the bottle. Screw thread Chapter 6 Simple Machines 93
1. Look at the three screws. Predict which screw would be the easiest to screw into the wooden block. 2. Take the screw with the least number of threads. 3. Screw it into the wooden block within 30 seconds. Measure the length of the screw that is left on the surface of the wooden block. 4. Repeat step 3 with the other two screws. Screw The length of the screw from the surface of the wooden block (mm) The least number of threads (A) More threads (B) The greatest number of threads (C) 5. If a hill is represented using these screws, which would take you a longer time to go up the hill from the same distance? Why? 6. Could you pull out the screws with your fingers? Why do we use tools? 7. What is your conclusion from this activity? Let’s Try! Which screw is easier to screw into a wooden block? • Wooden block • Screwdriver Things needed: • Three screws of the same length with a different number of threads Work in groups. List three simple machines (including the wedge on page 95) that can do the work in each of the following places: • In the kitchen • In the garden • In school • On the street Write down what they are, what kind of machine they are and what they are used for. Present your work in a table form. Let’s Find Out! 94 Hands-on Science Primary 5
Wedge A wedge is made up of one or two inclined planes. It has a sharp or pointed edge at one end. It is used to split an object apart by cutting, tearing or breaking it into two or more pieces. Some examples of wedges that are used for separating are shovels, axes, scissors or ice picks. A wedge can also be used to hold things in place. A doorstop is wedged under a door to prevent the door from moving. It is also used to keep or hold things together from moving. Some of the examples are push pins, nails or shims. A stapler is used to fasten together sheets of paper with a staple. A thumbtack is used to fasten paper to a softboard. A knife is used to cut an onion into slices. A saw is used for cutting wood or other hard materials into pieces. Chapter 6 Simple Machines 95