Effects of Force on Matter - Science PDF

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Nine Effects of force on matter LY...

FOR ONLINE USE ONLY DO NOT DUPLICATE Chapter Nine Effects of force on matter LY Introduction In Standards Three and Four, you learnt about the concept of matter. You learnt that matter is anything that has mass and which can occupy N space. There are three states of matter: solid, liquid and gaseous states. Matter is made up of many tiny particles that are interconnected. The O particles are made of molecules. Each molecule is made of atoms. Matter is important and has many uses. It can change from one state SE to another. You also learnt about three states of water, their properties and uses. The states of water are solid (ice), liquid and gaseous (steam) states. They show that water can change from one state to another. In this chapter, you will learn about force and how it influences changes U of the states of matter. You will also learn about physical and chemical changes of matter. E N Meaning and types of force LI Different objects or materials such as stones, metal and water are made up of small molecules that are connected or held together. What holds the N molecules together? Why don’t they fall apart? Definitely, the molecules that form these objects are connected or held together by certain O interactions. The interaction between one molecule and another is called force. Force is defined as the push or pull that acts upon an object. Force R can change the state of an object at rest or in uniform motion. The kind of forces that exist in molecules are called molecular forces. FO There are two types of molecular force. One is the intramolecular force that binds atoms to make a molecule. The other type is the intermolecular force that binds molecules. 140 SCIENCE AND TECHNOLOGY STD V.indd 140 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE The interaction of different kinds of intermolecular force is evident in different physical properties of the states of matter, that is, the solid state, liquid state and gaseous state. Solids The molecules in a solid have strong attraction forces between them. These forces are between the nucleus of an atom and the electrons of the other atom in the molecules. In a solid, attraction forces keep the molecules closely and tightly together so that the molecules do not move LY from place to place. The molecules are forced to vibrate in a fixed position. This causes solids to have a definite shape. Figure 1 shows how the molecules in solids are arranged tightly together by the strong attraction N forces. O SE U E N LI Figure 1: Molecules in solids N Liquids O The attraction forces between the molecules in liquids are weaker than those in solids. However, the forces are strong enough to keep the molecules close together. These forces cause continuous flow of R liquids. The molecules in liquids are randomly arranged compared to FO those of solids. Liquids have no definite shape and acquire the shape of the container when filled or stored in a container. Figure 2 shows how molecules in liquids are spaced and are free to move or slide over one another because the force of attraction between them is weak. 141 SCIENCE AND TECHNOLOGY STD V.indd 141 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE LY N O Figure 2: Molecules in liquids Gases SE The attraction forces between the molecules in a gas are weaker than those in liquids. Gases have no definite shape and they occupy the total volume of the container when filled or stored in a container. The molecules U in a gas are free to move because they are held together by very weak attraction forces. These molecules are randomly scattered compared to those of liquids, as shown in Figure 3. E N LI N O R FO Figure 3: Molecules in gases 142 SCIENCE AND TECHNOLOGY STD V.indd 142 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 1: Look at the arrangement of the molecules of matter shown in Figure 4 and answer the questions that follow. LY Solid Liquid Gas N O Figure 4: Arrangement of molecules in three states of matter Questions 1. SE Using Figure 4, explain the arrangement of molecules in solids, liquids and gases. U 2. Why are molecules arranged differently in the three states of matter? E Effects of heat on matter N When an object is heated, its molecules move more vigorously. For this LI reason, heat affects the attraction force in matter. When a solid is heated, the strongly held atoms vibrate within their fixed points. When a liquid N is heated, the molecules collide and move freely from one position to another position. The molecules in liquids are weakly held together and O the space between them is large. The molecules in a gaseous state are more free to move than in a liquid state because the attraction forces R between molecules are very weak. A small amount of heat causes gas molecules to move even faster. FO 143 SCIENCE AND TECHNOLOGY STD V.indd 143 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Uses of molecular forces Uses of molecular forces include: 1. Binding the molecules that form matter; 2. Enabling matter to be in different shapes and states; 3. Enabling chemical changes to occur; 4. Influencing various physical properties of matter such as boiling, LY freezing and melting points; and 5. Helping molecules to bind and work together. N The importance of molecular forces to living organisms O Molecular forces are very important to living organisms. They enable them to perform their functions. The following are examples of the areas where 1. SE molecular forces are important in daily life: The molecules in the body of a living organism such as proteins and genes are bound together using molecular forces. U 2. Water in plants is transported by molecular forces. 3. The properties of various substances such as water and soap are influenced by molecular forces. E 4. In industries, molecular forces are applied in the manufacturing of N various products such as iron, steel bars, spare parts, paint and oil. LI 5. The magnitude of force that exists in materials influences various properties such as boiling, melting and freezing points of liquids. N Physical and chemical changes O Physical and chemical changes are the main types of changes that occur in matter. R Physical change FO Physical change is a change that does not produce a new chemical substance; it only changes the state of matter. A good example of a physical change is the existence of water in the three states shown Figure 5. 144 SCIENCE AND TECHNOLOGY STD V.indd 144 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Increasing heat Increasing heat (Melts) (Boils) ICE WATER VAPOUR Decreasing heat Decreasing heat (Solidifies) (Condenses) Figure 5: Physical change of water LY Ice is water in a solid state. When ice is heated, it melts and becomes water. When the water that is in a liquid state is heated, it boils and becomes vapour, which is a gaseous state. When vapour is cooled it N becomes liquid. Water may freeze and become ice. Ice, water and vapour are different states of the same matter. Therefore, this implies that matter O can be changed from one state to another by increasing or decreasing temperature. The physical change of water does not affect the chemical properties of water. SE Experiment 1: Observing physical change U Aim: To identify the properties of physical change Materials: Wax, a pot, water, two cans and a stove E Procedure N 1. Pour the water into the pot and put the pot on the stove to boil the water. LI 2. Put the wax into the can. N 3. Put the can with the wax into the pot containing warm water and leave it there for five minutes. O 4. Remove the can with the wax from the pot containing warm water and put it into a container containing cold water. R 5. Allow the melted wax in the can to cool. FO Results When wax that is in a solid state is heated, it changes into a liquid state. But it changes again into a solid state after it has cooled. 145 SCIENCE AND TECHNOLOGY STD V.indd 145 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Conclusion The experiment shows that the change from solid to liquid and into solid again is a physical change. No new substance was formed. Chemical change This is a change that results in the formation of a new type of substance that cannot be changed back to its original form. Examples of chemical changes are the rusting of iron, the souring of milk and the burning of LY pieces of paper. Activity 2: Observing chemical change N Materials: Pieces of paper or any other combustible materials, a matchbox and a burning pit O Procedure 1. 2. SE Collect the pieces of paper or any other combustible materials. Put the pieces of paper into the burning pit. 3. Use the matchbox to ignite the pieces of paper, as shown in Figure U 6. What do you see? E N LI N O R FO Figure 6: Pupils burning pieces of paper in a pit 146 SCIENCE AND TECHNOLOGY STD V.indd 146 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE In this activity, it is observed that light, smoke, ash and heat are produced as a result of burning pieces of paper. This chemical change has produced ash and smoke. The ash and smoke are new types of substances that cannot be changed again into pieces of paper. Experiment 2: Identifying properties of chemical change Aim: To identify the properties of chemical change LY Materials: Sugar, a small pot, a stove and a matchbox Procedure N 1. Take one teaspoonful of sugar. O 2. Observe and record its colour and smell. 3. Put the sugar in the pot. SE 4. Light the stove and heat the pot containing the sugar. 5. Observe the heated sugar and record the observations. U 6. Increase the intensity of the flame and record the observations. 7. Turn off the stove when the sugar has boiled for a few minutes. E 8. Wait for the pot to cool. 9. Observe and record the colour, smell and taste of the remaining N materials in the pot. LI Results N 1. Are the properties of the sugar before and after heating similar? O 2. Is the substance or material left in the pot still sugar? R Conclusion Write the conclusion of the experiment you have done. FO 147 SCIENCE AND TECHNOLOGY STD V.indd 147 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Exercise 1 Answer questions 1 and 2 by choosing the correct answer. 1. The attraction forces between the molecules of matter are very weak in _______. (a) metal (b) water LY (c) air 2. Which one of these has a specific shape? N (a) A soft drink O (b) A piece of paper (c) Gas SE 3. Write TRUE for a true statement and FALSE for a false U statement. (a) The vibrations of molecules in solid matter are greater than those in liquid matter when heated. ____ E (b) When water boils to become vapour, it is a chemical change. N ____ LI (c) When wax is heated it changes its shape. ____ N (d) The attraction forces in solid matter and gaseous matter are the same. ____ O (e) The molecules in liquid matter are held together like in solid matter. ____ R (f) The burning of leaves and the souring of milk are chemical FO changes. ____ 148 SCIENCE AND TECHNOLOGY STD V.indd 148 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE Activity 3: Observing the results of grinding chalk Materials: A piece of chalk, a piece of a wooden board and a stone Procedure 1. Take the piece of chalk and put it on the piece of the wooden board. 2. Use the stone to grind the piece of chalk. 3. Gather the powder. 4. Compare the shape of the original piece of chalk and the chalk LY powder. 5. Write the results by answering the following questions: N (a) What is the state of the piece of chalk and the chalk powder? (b) What is the difference in shape between the piece of chalk O and the chalk powder? The chalk powder has been obtained by grinding the piece of chalk. The SE powder and the original piece of chalk are in a solid state. Therefore, the grinding of chalk did not change the state and nature of the piece of chalk. Instead, it changed its shape. This is physical change because U there is no formation of a new chemical substance. Activity 4: Observing the results of burning wooden sticks E Materials: A matchbox, dried wooden sticks and a piece of an iron N sheet Procedure LI 1. Pick up the dried wooden sticks and put them on the piece of the iron sheet. N 2. Ignite the wooden sticks using the matchbox. O 3. Make sure all the dried sticks are burnt completely. 4. Write the results by answering the following questions: R (a) What is the name of the residues on the piece of the iron sheet? FO (b) How do these residues differ from the sticks before they were burnt? (c) Is it possible to remake the wooden sticks from the residues? 149 SCIENCE AND TECHNOLOGY STD V.indd 149 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE When the sticks were burnt, they changed to pieces of charcoal and ashes. The charcoal and ashes were new chemical substances. They could not be converted back to wooden sticks. This is chemical change because new substances were formed. The difference between physical change and chemical change is shown in Table 1. Table: The differences between physical and chemical change Physical change Chemical change LY No new chemical substance is A new chemical substance is formed. formed. The original substance can be A new substance cannot be N easily regenerated after the changed back to the original change because the change is substance because the change is O temporary. permanent. The mass of the substance before The mass of the substance after and after the change is the same. the change is not the same. A little energy is used or is produced. SE A lot of energy is used or produced. The substance before and The new substance has different U after the change has the same properties from the properties of properties. the original substance. Exercise 2 E Answer the following questions. N 1. In the following changes, state whether the change is physical LI or chemical: (a) Rusting of iron N (b) Souring of milk O (c) Vapourisation of water (d) Making ugali using maize flour (e) Rotting of a plant R (f) Melting of wax FO (g) Burning of charcoal 150 SCIENCE AND TECHNOLOGY STD V.indd 150 7/30/21 11:03 AM  FOR ONLINE USE ONLY DO NOT DUPLICATE 2. In which state of matter is ice? 3. Which state of water may change and form clouds? 4. Give three differences between physical change and chemical change. Vocabulary Atom the smallest particle of a chemical element LY Force a push or pull that causes an object to move in a certain direction N Molecule the smallest particle in an element or compound that has the O chemical properties of that element or compound Nucleus the positively charged centre of an atom SE U E N LI N O R FO 151 SCIENCE AND TECHNOLOGY STD V.indd 151 7/30/21 11:03 AM