Sec 2 Science Summary Notes

CHAPTER 9: APPLICATION OF FORCES AND TRANSFER OF ENERGY *For G3 syllabus Only Contact force Non-contact force friction, elastic force, tension, normal contact force magnetic force, gravitational force (weight) Effects of forces • change in the state of rest or motion o start an object moving o stop a moving object o change the speed of a moving object o change the direction of a moving object • change the size and shape of an object • turning effect (e.g. spanners, levers) • pressure Magnetic force A magnet has two poles – a north pole (N) and a south pole (S). • Like poles repel each other • Unlike poles attract each other Mass Weight • the amount of matter in an object. • the gravitational force acting on an object. • SI unit: kilogram (kg) • SI unit: newton (N) • Remains constant regardless of location • May change with location • Measured with electronic or beam balance • Measured with spring balance Friction The force that opposes motion between two surfaces in contact. Friction can also take the form of air resistance and water resistance. Positive effects of friction Negative effects of friction • Friction enable us to have a grip to hold things and walk e.g. friction between our hands and a pencil, friction between shoes and the ground. • Friction slows things down and enable them to stop e.g. friction between the bicycle and the wheel. • Friction causes wear and tear e.g. friction between tyres and the road • Friction reduce the speed of objects e.g. water resistance acting on a swimmer Pressure is the measure of the amount of force acting on a unit area. 𝑃 = 𝐹 𝐴 forcepressure area= SI unit : N/m2 or pascal (Pa) Pressure depends on force and area in contact. How to increase pressure? • Increase the force • Decrease the area of contact e.g. sharp injection needle, small surface area of heel of high- heeled shoe, sharp knife *Pressure in liquid • The deeper the depth of the liquid, the higher the pressure. • Application of liquid pressure on submarines and dams. *Atmospheric pressure • Atmospheric pressure is 100 000 Pa at sea level. • Drinking straws and suction cup are used by creating a difference in the air pressure inside the straws / suction cup and the surrounding atmospheric pressure. How to decrease pressure? • Decrease the force • Increase the area of contact e.g. the heavy weight of an excavator acts on the caterpillar tracks which have a large contact area with the ground. Therefore, the pressure on the ground is low and hence, the excavator does not sink into the muddy ground. W = m x g Weight = mass x gravitational field strength (N) (kg) (on Earth g = 10 N/kg)

CHAPTER 9: APPLICATION OF FORCES AND TRANSFER OF ENERGY *For G3 syllabus Only * Work is done when energy is transferred through the application of force. THREE Conditions for Work to be done: 1. There is a force acting on an object. 2. The object moves. 3. The object moves in the direction of the force. W = F x d SI unit of Work: joule (J) More work is done when: 1. the force applied is larger 2. the distance moved by the object in the direction of the force is larger Destructive Power of Forces in Nature (Earthquakes, tsunamis, volcanic eruptions, tropical cyclones) Sources of Energy Impact on Environment 1. Fossil fuels Chemical potential energy → heat energy → kinetic energy (steam) → kinetic energy (turbine) → electrical energy Releases air pollutants and greenhouse gases (e.g. carbon dioxide) which causes global warming which lead to climate change and more intense natural disasters. 2. Solar energy Light energy → electrical energy Production and disposal of solar panels produces toxic waste. 3 Hydroelectric energy Gravitational potential energy → kinetic energy (water) → kinetic energy (turbine) → electrical energy Water floods areas behind the dam, killing plants and forcing animals to move. As fishes move, fishermen need to relocate. 4. Wind energy Kinetic energy (wind) → kinetic energy (wind turbine) → electrical energy (generator) Large plots of land must be cleared. Destruction of natural habitats hence potential loss of wildlife. Birds may collide into turbines. Noise pollution. 5. Geothermal energy Heat energy → kinetic energy (steam) → kinetic energy (turbine) → electrical energy Large areas of land need to be cleared, destroying wildlife habitats and affecting diversity of species. Traces of toxic elements may be drawn out from underground. 6. Biofuels Chemical potential energy → heat energy → kinetic energy Releases air pollutants when burnt. 7. Nuclear energy Nuclear energy → heat energy → kinetic energy (steam) → kinetic (turbine) → electrical energy Clean energy requiring less land. Potential risk to health & safety of nearby communities. Different forms of energy Kinetic Energy Energy possessed by a moving object. The faster an object moves, the more kinetic energy it has. Gravitational potential energy Energy stored when an object is lifted above the surface of the Earth. The higher the object, the greater its gravitational potential energy. Elastic potential energy Energy stored when objects are stretched, compressed or bent. Chemical potential energy Energy stored in substances, such as food and fuels. Principle of Conservation of Energy • Energy cannot be created or destroyed. • It can only be transferred from one form to another. • The total amount of energy in an isolated system is constant. Work = Force x Distance moved (in the direction of the force)

CHAPTER 10: TRANSFER OF HEAT ENERGY AND ITS EFFECTS *For G3 syllabus Only Transfer of Heat Energy When two objects are in contact, heat energy is transferred from an object of higher temperature to an object of lower temperature. S.I. unit of temperature: kelvin (K) Expansion and Contraction in Solids, Liquids and Gases Heating → Expansion Cooling → Contraction When temperature increases, particles gain energy and move further away from one another. When temperature decreases, particles lose energy and move closer to one another. Volume increases Volume decreases Mass remains unchanged Density decreases mD V  = Density increases mD V  = Applications of Expansion and Contraction Effect Precaution Buckling of railway lines Small gaps to allow for expansion Cracking of concrete surfaces Snapping of overhead wires Allow extra length of wire Expansion/Contraction of bridges One end of bridge is fixed while the other end is free to move over rollers Bursting of pipes carrying hot water ‘Expansion loops’ For the same rise in temperature: Expansion of gas > liquid > solid For the same fall in temperature: Contraction of gas > liquid > solid Bimetallic strips Unequal expansion and contraction of two metals. Used in thermostats, fire alarms etc.

CHAPTER 10: TRANSFER OF HEAT ENERGY AND ITS EFFECTS *For G3 syllabus Only Conduction Convection Radiation Definition Conduction is the transfer of heat energy through a medium or material without the physical movement of the medium. Convection is the transfer of heat energy by convection currents in a fluid (liquid or gas), due to a difference in density. Radiation is the transfer of heat energy, in the form of waves such as infrared radiation, without the aid of a medium. Notes Best in solids, then liquids, then gases. In liquids and gases only. In solids, liquids, gases and vacuum. Metals are good conductors of heat as they have free electrons. Heat from Sun reaches Earth by radiation. Explanation Particles gain heat and vibrate faster. These particles collide with neighbouring particles, transferring energy and causing them to vibrate faster too. When the water at the bottom of the fla