science sec 2

• Strong winds can exert great forces on objects such as vehicles, buildings, trees, and people
• Contact Forces:

  • Forces acting between two objects in physical contact
  • Examples: Friction, Elastic force
• Friction is the force that opposes motion between two surfaces in contact
• Elastic force is the force acting on a stretched or compressed elastic object to return to its original shape
• Non-contact Forces:

  • Forces acting between two objects not touching each other
  • Examples: Gravitational force, Magnetic force
• Gravitational force attracts two objects towards each other
• Magnetic force is exerted between a magnet and another magnetic material like iron or steel
• Weight is the measure of gravitational force acting on an object, with the SI unit being newton (N)
• Mass is the amount of matter in an object, with the SI unit being kilogram (kg)
• Weight may change with location, while mass remains constant regardless of location
• Pressure is defined as force per unit area
• When the area of contact increases, pressure decreases and vice versa
• Energy can be converted from one form to another
• The total energy of something remains constant and does not increase or decrease
• Gravitational potential energy increases as something goes up and converts to kinetic energy as it goes down
• Most energy on Earth comes from the Sun, supporting life through photosynthesis and growth of plants
• Fossil fuels are formed from dead plants and animals, limited and non-renewable
• Burning fossil fuels releases heat energy used to produce electricity in power stations
• Solar energy is renewable, derived from sunlight, and converted to electrical energy
• Hydroelectric energy is renewable, derived from fast-flowing rivers, and converted to electrical energy
• Wind energy is renewable, derived from strong wind, and converted to electrical energy
• Geothermal energy is renewable, derived from hot water underground, and converted to electrical energy
• Biofuels are renewable, derived from food waste/plants, and converted to electrical energy
• Nuclear energy is renewable, derived from nuclear fission, and converted to electrical energy
• Temperature is the measure of how hot an object is
• Temperature can be measured more accurately using scientific instruments such as a thermometer
• A thermometer is used to measure changes in temperature resulting from the transfer of heat
• The SI unit of temperature is Kelvin (K)
• When two objects are in contact, heat energy is transferred from the hotter object (of a higher temperature) to the colder object (of a lower temperature), causing the temperature of the colder object to increase and the temperature of the hotter object to decrease until they reach the same temperature
• Heat energy is transferred from the water in the basin to the water in the beaker, increasing the temperature of the water in the beaker
• Heat energy is transferred from the water in the beaker to the ice cubes, decreasing the temperature of the water
• The transfer of heat energy can cause objects or substances to expand or contract
• Expansion and contraction can take place in solids, liquids, and gases
• In solids:

  • In hot weather, a metal railway track gains heat and expands, potentially causing buckling
  • Concrete bridges expand in hot weather and contract in cool weather, with expansion joints and rollers allowing for safe expansion and contraction
• In liquids:

  • Oceans absorb heat energy, causing them to expand and the sea level to rise, leading to coastal erosion
• Metal pipes expand and contract based on temperature and substances they carry, with flexible bands allowing for safe expansion and contraction
• The effects of expansion and contraction due to the transfer of heat energy can be applied in daily life, such as opening a jar by using hot water to expand the lid more than the glass jar
• A bimetallic strip consists of two different metals joined together, expanding at different rates when heated, used in bimetallic thermometers, circuit breakers, and thermostats
• In a liquid-in-glass thermometer, the liquid expands and rises up the narrow glass tube when heated, and contracts and falls back into the bulb when cooled
• In a hot air balloon, heating the air inside increases its volume, decreasing its density and causing it to rise, while the air inside a deflated balloon has the same temperature as the outside air