Sec 2 Sci 10

• Place your left hand in cold water, and your right hand in warm water. How does each hand feel? Next, place both your hands in water at room temperature. Although your hands are placed in water of the same temperature, your right hand feels cooler than your left hand
• Temperature is the measure of how hot an object is. Apart from using one's senses, temperature can be measured more accurately using scientific instruments such as a thermometer
• In daily life, we measure temperature in degree Celsius (°C) or degree Fahrenheit (°F). In science, the SI unit of temperature is Kelvin (K)
• Transfer of heat energy

  1. Hotter object transfers heat energy to colder object

  2. Temperature of colder object increases

  3. Temperature of hotter object decreases

  4. Temperatures equalise
• 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)
• Expansion and contraction


  • When a substance is heated, it gains heat and expands (increases in volume)
  • When a substance is cooled, it releases heat and contracts (decreases in volume)
• Expansion and contraction in solids


  • Railway track expands in hot weather, may buckle
  • Concrete bridge expands in hot weather, contracts in cool weather, may get damaged
• Expansion gaps and expansion joints

  Provide space for expansion and contraction of solids
• Climate change causes oceans to absorb more heat energy, leading to expansion and sea level rise, which increases coastal erosion
• Metal pipes carrying steam or hot water are built with flexible bends to enable expansion and contraction without breaking
• Bimetallic strip

  Made of two metals that expand at different rates upon the same change in temperature
• Applications of bimetallic strip

  • Used in thermostats and bimetallic thermometers
  • Used in electric irons to switch off when set temperature is reached
  • Used in food thermometers to measure temperature
• Liquid-in-glass thermometer

  Liquid in the bulb expands and rises up the tube when temperature increases, contracts and falls back when temperature decreases
• When air in a hot air balloon is heated, its volume increases, density decreases, causing the balloon to rise
• Heat energy can be transferred by conduction, convection, and radiation
• Conduction


  Transfer of heat energy without the physical movement of the medium
• Metals are better conductors of heat than non-metals
• Solids are generally better conductors of heat than fluids (liquids and gases) due to the closer arrangement of particles
• The can feels colder than the carton
• Metals conduct heat better than non-metals
• Good conductors of heat

  • Metals such as aluminium, iron, steel and mercury
• Poor conductors of heat

  • Non-metals such as wood, paper, glass and plastic
  • Liquids
  • Gases
• Solids are generally better conductors of heat than fluids (liquids and gases)
• The close arrangement of particles in solids enables the transfer of heat energy to occur more quickly
• Convection


  The transfer of heat energy from one place to another by the physical movement of a medium
• Convection in liquids

  1. Heated water expands, becomes less dense, and rises

  2. Cooler and denser water sinks

  3. Convection currents are formed

  4. Heat energy is transferred throughout
• Convection in gases

  1. Hot air rises

  2. Cooler air moves down to replace the hot air

  3. Cycle of convection currents is formed
• Radiation

  The transfer of energy from a hotter body to a cooler body without the need for a medium
• Heat energy can be transferred from the sun to Earth by radiation
• Energy from the sun can be absorbed or reflected by the atmosphere and Earth's surface
• Greenhouse effect


  The warming of the surface of Earth caused by heat being prevented from leaving Earth's atmosphere by radiation
• Greenhouse gases trap heat within the atmosphere and keep Earth warm
• Burning of fossil fuels increases the amount of greenhouse gases in the atmosphere, leading to global warming
• Effects of global warming include melting of polar ice caps and glaciers, and rising sea levels
• Environmental scientists

  • Discover new knowledge related to the environment
  • Use knowledge to protect the environment and human health
  • Develop plans to prevent, control or resolve environmental problems
  • Test and analyse environmental samples
  • Advise policymakers on environmental issues
• Singapore has built sea walls and rock structures to protect its coastline from erosion
• Coral reefs protect coastlines from natural disasters and rising sea levels
• Coral bleaching occurs when corals force out the algae that live in them due to increased seawater temperature
• Scientists are experimenting with creating new breeds of coral that can survive extreme heat
• Different materials conduct heat at different rates