Chapter 9 Application of Forces Part 1 2025 Slides PDF

Chapter 9 Application of Forces and Transfer of Energy Application of Forces and Transfer of Energy 9.1 How Do Forces in Nature Affect Us? 9.2 What are the types of Forces? 9.3 What Happens When Two or more Objects Interact? 9.4 How Is Energy Conserved? 9.5 What Are...

Chapter 9 Application of Forces and Transfer of Energy Application of Forces and Transfer of Energy 9.1 How Do Forces in Nature Affect Us? 9.2 What are the types of Forces? 9.3 What Happens When Two or more Objects Interact? 9.4 How Is Energy Conserved? 9.5 What Are the Sources of Energy We Use? Forces of Nature Forces of nature can be very large and destructive Forces of nature includes: Tropical Cyclones Volcanic eruption Tsunamis Earthquakes Hurricane/typhoon © 2013 Marshall Cavendish International (Singapore) Pte Ltd  Forces of Nature © 2013 Marshall Cavendish International (Singapore) Pte Ltd  Destructive forces of nature around the world in Dec 2021 Typhoon in Earthquake in Philippines Indonesia Massive flood in Malaysia © 2013 Marshall Cavendish International (Singapore) Pte Ltd 9.1 How Do Forces in Nature Affect Us? Class Discussion 9.1.1 Activity Book 2A pg 1-3 The Destructive Nature of Natural Disaster 9.2 What are the types of Forces A force can be a ‘push’ or a ‘pull’. Boy exerts a push on the Boy exerts a pull on boat the boat Examples of Forces Squeezing Twisting Stretching Pulling Pressing  9.2.1 Forces Around Us Non-Contact Force Contact Force Gravitational Force Frictional Force Magnetic Force Friction and Its Effects Frictional force Friction occurs when two objects are in physical contact with each other. The diagram below shows a microscopic view of two surfaces in contact. Friction and its Effects Friction always opposes motion between two surfaces in contact. Friction is a contact force. It is a force due to two surfaces in contact with each other. Friction is greater when an object moves on a rough surface than on a smooth surface. Friction has both positive and negative effects in our lives Friction and Its Effects Negative effects of friction Friction produces heat which results in wastage of energy. Causes wear and tear of moving parts in engines, motors and machines. Friction and Its Effects Positive effects of friction Needed for walking or holding a pair of chopsticks Used in braking pads to slow down cars Friction and Its Effects Ways to reduce friction include: Wheels Ball Bearings Lubricants and polishing surfaces Air cushion e.g. hovercraft Friction and Its Effects Friction as a useful force Friction can also be useful for our daily lives. Examples include: Car tyres Parachutes Shoes for Rock climbing Magnetic Force Magnetic force is a force of attraction between magnets and magnetic material. It can also refer to the force of attraction or repulsion between magnets. Magnetic Force Not all metals can be attracted by magnets. Only magnetic materials or alloys of magnetic materials can be attracted by magnets. Common magnetic materials and alloy: – Cobalt – Iron – Nickel – Steel Magnetic Poles The two ends of the bar magnet where the magnetic effects are the strongest, are called the poles of the magnets. Law of magnetic poles Like poles repel, unlike poles attract. Force of Attraction Force of Repulsion Uses of Magnets Compass Maglev Train Gravitational Force The gravitational force of the Earth pulls all objects towards its centre of the Earth. Weight is the gravitational force exerted by the Earth on the object. Gravitational field strength is the amount of gravitational force acting on 1 kg mass The gravitational field strength on Earth denoted by g which has a value of 10 N/kg The weight of an object that has a mass of 1 kg is 10 N on Earth Gravitational Force 9.2.2 Comparing Mass and Weight Weight and mass are often used interchangeably in our ordinary conversation. In science, weight and mass are two different quantities, each with their own physical units. earth moon weight weight Mass on the earth = 60 kg Mass on the moon = 60 kg Weight on the earth = 600 N Weight on the moon = 100 N Mass Mass is a measure of the amount of substance in a body. a) S.I. unit: kilogram b) Mass does not change with locations. (it is the same on earth or on the moon) Mass The measuring apparatus for mass are the beam balance or the electronic balance. Beam balance Beam balance is used to measure mass Electronic balance Electronic balance is used to measure mass Weight a) Weight is the gravitational force exerted on object. b) Measured using a spring balance. c) S.I. unit: Newton d) May change with location Spring balance Spring balance is used to measure weight  Differences between mass and weight Mass Weight matter 1. the amount of _________ 1. the gravitational ______ force in an object. exerted on an object. 2. Remains 2. varies according to regardlessconstant of location gravitational field strength. 3. measured using a 3. measured using a _________ beam or ___________ spring balance. ____________ balance. electronic kilogram 4. S.I. unit: __________ newton 4. S.I. unit: __________ Mass and Weight Mass and weight The force of gravity (weight) is different on different massive objects, e.g. planets. The weight of a person on the earth is greater than his weight on the moon. This is due to the stronger gravitational field strength on the earth. Gravitational field strength on the Earth = 10 N/kg. Gravitational field strength on the Moon = 1.6 N/kg. 9.3 What Happens when two or more objects interact? A force can Change the shape of an object Change the size of an object Make a stationary object move Effects of Forces A force can Change the direction of a moving object Change the speed of a moving object Stop a moving object A force cannot change the mass of an object.  Moment of a Force: Turning Effect of Forces A force can have a turning effect. steering wheel see-saw swing 9.3.1 Effects of Forces Examples of turning effect of forces Using a crowbar Using a fishing rod A person applies a force on the A person applies a large force on the handle of a crowbar. The crowbar fishing rod handle to lift the fishing turns and pulls out the nail from the rod. The fish that is caught at the wooden plank. other end of the rod moves over a large distance. Force Force Turning effect Turning effect 9.3.1 Effects of Forces Examples of turning effect of forces Force Using a wheelbarrow A person applies a Turning effect upward force on the handles of a wheelbarrow. The heavy load becomes easier to move. 9.3.2 Pressure 1. What is pressure? 2. How to relate pressure and area and force? 3. How to calculate pressure Optional for G2 4. Applications of pressure?  Pressure is defined as the force acting per unit area  Let’s look at an example Force Force Thumbnail Thumbnail 1 2 Cardboard Which thumbnail will make a hole in the cardboard easily?  Force Force Thumbnail Thumbnail 1 2 What can you say about the area? What is the explanation behind?  Force Force Thumbnail Thumbnail 1 2 Area touching cardboard Area touching cardboard is small is large A sharp object pierces a surface more easily than a blunt object  Optional for G2 Pressure Force Area = S I unit: Pascal ( Pa ) 1 Pa = 1N/m 2 Which position will the block exert more pressure on the ground? Optional for G2 Force = 10 N Force = 10 N B A 2m 2m 10 m 2m Area touching the floor = L x W Area touching the floor = L x W = 10 m x 2 m = 20m2 = 2 m x 2 m = 4m2 Pressure = Force / Area Pressure = Force / Area = 10 N / 20m2 = 10 N / 4m2 = 0.5 N/m2 = 2.5 N/m2  Optional for G2 Which cube exerts more pressure? Force = 8 N Force = 16 N B C 2m 4m 2m 4m Area touching the floor = L x W Area touching the floor = L x W = 2 m x 2 m = 4 m2 = 4 m x 4 m = 16 m2 Pressure = Force / Area Pressure = Force / Area = 8 N / 4 m2 = 16 N / 16 m2 = 2 N/m2 = 1 N/m2 9.3.3 Applications of Pressure in Everyday Life ⚫Bulldozer ⚫Can openers ⚫Knife ⚫Plane ⚫Suction cups  Optional for G2 Class 9.3.3 Activity Book 2A pg 23-26 What are the Daily Life Phenomena Associated with Pressure?  Optional for G2 Applications of Pressure in Everyday Life 1.Pressure due to water depends on the depth of water. 2.The deeper the water, the higher the pressure. 3.The shallower the water, the lower the pressure.  Optional for G2 Applications of Pressure in Everyday Life ⚫ Suction cups work because the atmospheric pressure outsid e pushes down on it and holds it firmly in place. ⚫ Suction cups will hold on until either the cup is lifted from the side allowing air in and makes pressures equal or by applying a force large enough to overcome atmospheric pressure Other places where pressure plays a role? Sling bag Haversack Applications of pressure in daily lives: https://www.youtube.com/watch?v=5UnNfkX3Qc4  Optional for G2 Example ⚫Calculate the pressure exerted by a 300 N force over an area of 0.5 m2. P = 600 Pa  Optional for G2 Example ⚫The wind exerts a pressure of 150 Pa on a wall. The dimensions of the wall are 2 m by 3 m. What is the force that the wind exerts on the wall? F = 900 N  Optional for G2 Example ⚫A force of 250 N is exerted on an area with 50 Pa of pressure. Calculate the contact area. A = 5 m2  Optional for G2 Example A block of wood 6 m long, 3 m wide and 0.5 m thick is placed on a table. If weight of the block of wood is 4 5000 N , what is the pressure on the table due to the block? (Take g = 10 m/s2) F p= A Area = 6 X 3 = 18m2 (Note: Weight is a type of force) p =F/A ∴ p = 45000 / 18 = 2500 Pa  Optional for G2 Example An Eskimo stands on snow wearing snow-shoes. The mass of the Eskimo is 40 k g. Each side of the snow-shoe has an area of 0.25 m2. What pressure does the Eskimo exert on the snow? F p= A Area = 0.25 X 2 = 0.5 m2 F = Weight = 40 x 10 = 400 N (Note: Weight is a type of force) p =F/A ∴ p = 400 / 0.5 = 800 Pa