Science WA2

• Contact forces


  Forces acting between two objects that are in physical contact with each other
• Contact forces


  • Friction
  • Elastic force
• Friction


  The force that opposes motion between two surfaces in contact
• Elastic force


  The force acting on a stretched or compressed elastic object to return it to its original shape
• Non-contact forces


  Forces acting between two objects that are not touching each other
• Non-contact forces

  • Gravitational force
  • Magnetic force
• Gravitational force


  A force that attracts two objects towards each other
• Magnetic force


  A type of non-contact force exerted between a magnet and another magnetic material such as iron or steel
• Magnets


  • Every magnet has a north pole and a south pole
  • Unlike poles of magnets attract
  • Like poles of magnets repel
• Weight


  The measure of the gravitational force acting on an object
• Mass


  The amount of matter in an object
• When a 10 kg bag of rice is placed on the moon

  The mass remains the same, but the weight is smaller than on Earth due to less gravitational force
• Changes in the state of rest or motion of an object

  1. Move a stationary object

  2. Change the speed of an object

  3. Change the direction in which an object moves

  4. Stop a moving object
• When two or more objects interact, they exert a force on one another, resulting in the transfer of energy between the objects
• Turning effect of a force on an object

  • A force applied on an object can cause a turning effect about a fixed point called the pivot
  • This turning effect can help carry out an action with less force, such as removing the lid of a tin can or tightening a nut
• Turning effect of a force

  • Pressing down on the handle of a fork to easily remove the lid of a tin can
  • Turning the handle of a spanner to tighten a nut easily
• Changes in size and/or shape of an object


  • The transfer of energy between objects may cause changes in the size and/or shape of an object
• Changes in size and shape


  • Balloon changes in size when air is pumped into it
  • Sponge changes in shape when a force is applied to it
• Pressure


  An effect of force acting on an object
• Factors affecting pressure


  • Whether carrying a backpack using one or two straps
  • How much the contents of the backpack weigh
• Area of contact


  Affects the pressure exerted by an object
• Pressure exerted by objects

  • Pin pushed into cork board easily due to high pressure from small area of contact
  • Nail pushed into cork board with difficulty due to low pressure from large area of contact
• Calculating pressure


  Pressure = Force / Area
• The unit of pressure is newton per square metre (N/m^2), also known as the pascal (Pa)
• Pressure in everyday life

  • Sharp injection needle pierces skin easily due to high pressure
  • High-heeled shoe exerts higher pressure on mobile phone screen than sneaker
  • Sharp knife cuts tomato more easily than blunt knife due to higher pressure
• Pressure in liquids


  • Pressure increases as you swim deeper underwater
  • Base of a dam has thicker wall than top due to higher water pressure at the base
  • As sea levels rise, the base of a dam needs an even thicker wall
• Pressure in submarines


  • Submarines need a strong body to withstand the high pressure deep underwater
  • Submarines have a depth meter to ensure they stay at a safe depth where pressure is not too high
• Atmospheric pressure


  Earth is surrounded by the atmosphere, which exerts pressure on the surface
• Elements


  The basic building blocks of living and non-living matter that cannot be broken down into simpler substances
• The diversity of matter is made up of one or more elements in the periodic table
• Compounds


  Two or more elements that are chemically combined together
• Mixtures can be made up of:

  • Elements only (Figure 3.10)
  • Compounds only (Figure 3.11)
  • Both elements and compounds (Figure 3.12)
• Properties of Mixtures


  • Have the same characteristics as their constituents
  • Constituents do not have a fixed proportion
  • Constituents can be easily separated from the mixture
• Solution


  A mixture in which one substance (solute) dissolves completely in another substance (solvent)
• In a solution, the particles of the solute can no longer be seen and light can pass through it fully
• Compounds do not have the same properties as their constituent elements
• The constituent elements of a compound are always chemically combined in a fixed proportion by mass
• A compound cannot be separated into its constituent elements easily
• Dilute solution


  A solution with a low percentage of dissolved solute
• Concentrated solution


  A solution with a high percentage of dissolved solute