chapter 9

• examples of destructive forces

  1. tsunamis
  2. earthquakes
  3. volcanic eruptions
  4. topcial cyclones
• tropical cyclones

  1. cause of tropical cyclone -> the increase in temperature of sea surfaces caused by climate change leads to longer and more intense storms that begin over warm oceans in the tropical regions.
  2. tropical cyclones are accompanied by heavy rain and strong winds
  3. due to the heavy rain, flooding occurs
  4. the rapid moving floodwater exerts forces on the soil and loosen it causing landslides
• destruction caused by tropical cyclones

  1. the wind speeds in tropical cyclones can go up to about 200km/h
  2. strong winds exerts great force on object that are in their way, eg: vehicles, buildings, trees, people
  3. the broken parts of objects that are carried in the air by the strong winds can cause more damage to surrounding objects or even hit and injure people
• earthquakes

  1. the surface of the earth is made up of many huge pieces of solid rock called plates. the plates move very slowly and continuously.
  2. earthquakes are caused when there is a great amount of energy released by the forces exerted between a plate sliding over/against another plate
  3. earthquakes are also tremors
• volcanic eruptions

  1. deep in the earth, rocks melt to become magma due to the high temperature
  2. volcanic eruptions occur when magma is pushed out words the earth’s surface with great force together with the earth moving violently.
  3. a great amount of energy stored within the earth is released as heat, light and kinetic energy of the magma.
• destruction caused by volcanic eruptions

  1. causes serious destruction to nearby towns and villages
  2. ash cloud causes air travel disruptions ->volcanic ash can stay in the atmosphere for a long time. this affects the travel arrangements of hundreds of thousands of people. from aerial view [view from a great height above ground], the ash cloud would look dense
• tsunami

  1. when the earthquakes and volcanic eruptions that occur beneath the ocean are strong enough, they trigger a series of powerful waves known as tsunamis
  2. tsunamis occur when vigorous movement of the ocean floor caused by earthquakes or volcanic eruptions displaces the ocean water
  3. the waves are estimated to reach heights of up to 40m
• energy transfer in tsunami

  1. due to the high waves, the potential energy of the ocean water increases greatly
  2. as the waves move at high speed towards the shore, the potential energy in the waves is converted to kinetic energy.
  3. this results in the powerful waves hitting the shore and striking objects along the shore with great force
• how the acceleration of climate change could affect Singapore's food supply

  1. Tropical cyclones are increasing in intensity and duration because of climate change. Scientists have related this to an increase in surface temperature of the sea. When natural disasters occur, sea and air transport is disrupted. This threatens global food and goods supply. As Singapore imports a large percentage of our food supply, it may be affected by such natural disasters.
• force

  1. a force is a push or a pull
  2. examples of actions of forces -> lifting, stretching, pressing, twisting
  3. effects of forces -> move a stationary object, stop a oving object, change the speed of a moving object, change the direction of a moving object
• contact forces

  • forces acting between two objects that are in physical contact with each other
  • examples of contact forces -> frictional force, elastic force
  • frictional force is the force that opposes motion between two surfaces that are in contact
  • elastic force is the force acting on a stretched or compressed elastic object to return to its original shape
  • when an elastic material is stretched or compressed. it resists the change in shape by exerting a force in the opposite direction
• non-contact forces

  1. forces acting between two objects that are not touching each other
  2. examples of non-contact forces -> gravitational force, magnetic force
  3. gravitational force is the force that attracts two objects towards each other.
  4. an object is known to have weight when a planet exerts gravitational force on it and pulls it towards the centre of the planet
  5. the weight of an object is the amount of gravitational force acting on it
• fun facts

  • during low tide, the sea bed is exposed. during high tide, the water level rises and the sea bed is covered by the sea. this is due to the effect of gravitational force exerted on the water by the moon. as the moon is big, it it able to exert a large gravitational force on the seawater on earth. the gravitational force on the water changes as the earth rotates. the water that is facing the moon will experience a larger gravitational force, resulting in high tide
• fun fact

  • the earth behaves like a magnet. the compass that we use to find our way has a magnetic needle that points to the magnetic north pole of the earth. some animal [eg: birds and turtles] can sense the earth‘s magnetic field and use the magnetic field as a guide to navigate long distances when they migrate
• magnetic force

  • magnetic force is the force exerted between a magnet and another magnetic material such as iron or steel [CoINS]
  • every magnet has a north pole and a south pole.
  • when unlike poles are brought close together, the pull together due to the magnetic force of attraction.
  • when like poles are brought close together, they push apart due to the magnetic force of repulsion
• maglev train

  • the maglev train sorks on the principle of magnetic repulsion between the train and the track.
  • the maglev train floats on air due to the magnetic repulsion of like poles. this reduces the friction between the train and the track, allowing the train to travel at a higher speed/
  • maglev -> magnetic + levitation [floating]
• weight

  • weight is the measure of the gravitational force acting on an object.
  • the SI unit of weight is Newton, N.
  • the weight of an object can be measured by using a spring balance. the spring in an spring balance stretches when a force pulls on it.
  • the weight of an object can be read off directly from the scale on the spring balance
  • the weight of an object depends on the gravitational force exerted on the object, which may change with its location
• spring balance

  1. ensure that the 0 mark of the scale is in line with the pointer, if it isnt, move the scale by pushing or pulling the tab until the 0 mark is in line with the pointer
  2. apply the force to be measured on the hook
  3. read the scale to the nearest 1 decimal place
• mass

  • mass is the amount of matter in an object.
  • the SI unit of mass is kilogram, kg
  • the mass of an object remains the same regardless of its location as there is no change in the amount of object
  • an electronic balance/beam balance is used to measure mass
• turning effect on objects

  • a force applied on an object can cause a turning effect about a fixed point called the pivot, this can help us to carry out an action with little force
  • eg: opening a tin with a fork is easier than using your bare hands. when a downward fotce is applied on the handle of the fork, the fork applies an upward force at the small edge of the tin [pivot]. this results in a greater turning effect, making the lid easier to turn
• change in size/shape of an object

  • the transfer of energy between objects may cause changes in the size and/or shape of an object
  • changes to state to rest or motion of an object
  • turning effects in objects
  • changes to size and/or shape of an object
  • changes to pressure on objects

  A FORCE CANNOT CHANGE THE MASS OF AN OBJECT
• therefore, the effects of forces when force applied are

  • speed of object changing
  • shape of object changing
  • direction of motion of object changing
  • size of object changing
  • turning effect of object
• pressure

  • pressure is the effect of force acting on an object
  • factors affecting the amount of pressure acting on an object -> area of contact with the surface, amount of force applied on the surface
  • pressure is defined as force per unit area
  • pressure = force divided by area, where the amount of force applied is measured in newton, and the are of contact is measured in square metre [m2]. the unit of pressure is newton per square metre [N/m2], also known as pascal [Pa]
• effect of area on pressure

  • the smaller the contact area, the higher the pressure exerted
  • the larger the contact area, the lower the pressure exerted
  • eg: the area of contact of block A is smaller than block B. for the same amount of force [weight] applied, the pressure exerted by block A will be larger than black B
• effects of force on pressure

  • when both objects have the same area of contact, we have to consider the amount of force applied to it.
  • when more force is applied to the object, a greater pressure is exerted on the [surface], allowing the object to sink deeper
• liquid pressure

  • in a water bottle filled with water, the water at the bottom has the highest pressure, the weight of the water particles pushing down on the bottom of the water bottle creates more pressure at the bottom of the water bottle
• depth limit

  • a submarine has a recommended depth limit to dive underwater as when the pressure increases when the depth increases, sumarines need a strong body to withstand the high pressure when they dive down. there is a recommended depth limit as they need to ensure that the submarine is at a safe depth where the water pressure is not high enough to damage its physical structure
• atmospheric pressure

  • air particles experience gravitational force
  • the earth is surrounded by a thick layer of air which exerts pressure on us and all objects on earth
  • the pressure exeted by air is called air pressure/atmospheric pressure
  • the thick layer of air around the earth exerts a pressure of approximately 100 000Pa at sea level
  • at the top of the moutain, there are few air particales pushing down on the surface. so, the atmospheric pressure is lower
• eg of how pressure works in our everyday lives:

  • drinking straws, they work on the difference in air pressure. when you suck on the straw, some air is removed from the drink. the air pressure inside the straw decreases and becomes lower then the surrounding atmosheric pressure. the higher atmospheric pressure from the surrounding air forces the liquid up the straw and into your mouth.
• forms of energy

  1. Electrical energy can be used to power electrical appliances like the television and the electric fan.
  2. Sound energy enables us to listen to our favourite music.
  3. Light energy allows us to see things.
  4. Heat energy enables us to warm our food.
  5. Chemical potential energy in batteries can be used as an energy source when converted into electrical energy.
  6. Gravitational potential energy which an object possesses due to its position can cause an object to move faster when converted into kinetic energy.
• energy

  • energy is the capacity to do work
  • the SI unit of energy is joule (J)
  • energy can be transferred from one place to another
  • energy can change the state of matter
  • energy can be converted or transformed from one form to another
• conservation of energy

  • conservation of energy is a scientific principle which states the total energy always remains constant, as energy cannot be created or destroyed but can be converted from one form to another
• limitations of energy production

  • insufficient land
  • lack of natural resources -> import ALL of our fuel
  • unable to implement renewable energies because of geographical restraints
• advantages of energy production

  • 95% of our electricity is generated using natural gas -> 95% natural gas, 5% diesel, fuel oil and others
  • the establishment of the SLNG [singapore liquefied natural gas] terminal allows us to import liquefied natural gas from all over the world
  • the natural gas we import is mainly used by power generation companies to generate electrcity
  • previously, we could only depend on malaysia and indonesia for piped natural gas
• CCGT [combined cycle gas turbine]

  • uses both steam and gas turbines to produce more electricity from the same fuel as compared to steam turbines
  • in the gas turbine, chemical energy of the natural gas is converted to kinetic energy of the turbine. this kinetic energy is then converted to electrical energy via a generator.
• solar energy

  • right now, the most viable source of renewable energy is solar energy
  • if we have a cloud cover, the supply would be intermittent
  • on average, we only get 5 hours of sunlight
  • even is we cover all of singapore with solar panel, we still wouldn’t be able to meet our energy requirements. so, we use natural gas, which is more reliable, to generate electricity
  • singapore experiences less than 1 min of disruption per customer per year
• energy transportation

  • as singapore has limited land, we shifted our electricity cables underground
  • the electricity transmission main artery is located 60m below ground and its 60m deep and 35km long
• transmission cables

  • singapore also has other underground infrastructure, such as the singapore district cooling system under marina bay. it provides chilled water for air conditioning to buildings such as marina bay sands.
  • this frees up space above ground for other uses
• power system control centre

  • we use the condition monitoring system to predict and avert downtime and disruption. this allows a better allocation of resources
  • nerve centre of electricity generation and transmission system
  • ensures security of supply of electricity to consumers
• smart meters

  • we use them to tell consumers how much electricity they are using so that they can adjust their energy use and save money