S2 Science

• Type of forces

  Contact force non-contact force

  -friction -magnetic force

  -elastic force -gravitational force

  (Weight)
• Definition of friction:

  The force that opposes motion between two surfaces in contact
• Friction:

  Positive Things about friction:

  -enable us to have a grip to hold things and walk

  -slows things down and enable them to stop

  Negative things about friction:

  -causes wear and tear

  -reduces the speed of objects
• Gravitational field strength(formula):

  W= m x g
• Deifinition of weight

  The gravitational force acting on an object
• Definition of mass

  The amount of matter in an object
• Weight

  SI Unit = Newton (N)

  -may change witht location

  -measured with a spring balance

  -----------------------------------

  Mass

  SI Unit = Kilogram (Kg)

  -remains constant regardless of location

  -measured with electronic or beam balance
• Effects of forces

  •Change in the state of rest or motion

  -start a moving object♡

  -change the speed of a moving object☆

  -change the direction of a moving object♤

  •change the size and shape of an object◇

  •turning effect♧(e.g. spanners, levers)
• Pressure is the measure of the amount of force acting on a unit area
• Formula:

  Force

  Pressure = -----------

  Area

  SI unit = pascal ( Pa )
• Pressure depends on force and area in contact
• How to increase pressure?

  -○increase the force○

  -♡decrease the area of contact♡

  ---‐-‐----------------------------

  How to decrease pressure?

  -♧decrease the force♧

  -♤increase the area of contact♤
• 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 °~°
• Formula=

  Work = Force x Distance moved in the direction of the force
• 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
• Different forms of energy -kinetic energy•~• -gravitational potential energy°~° -elastic potential energy°▪︎° -chemical potential energy°○°

  -heat energy○□○

  -light energy•◇•

  -sound energy☆^☆

  -electrical energy×○×
• 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
• ☆Fossil fuels

  Chemical potential energy > heat energy > kinetic energy(steam)>kinetic energy(turbine) > electrical energy

  -----------------------------------

  ☆Impact on environment

  -releases air pollutants and greenhouse gases which leades to global warming which leads to climate change and more intense natural disasters °-°
• •Solar energy

  Light energy > electrical energy

  --------------------‐---------------

  Impact in environment

  -production and disposal of solar panels produces toxic waste°▪︎°
• •Hydroelectric energy

  Gravitational potential energy > kinetic energy(water) > kinetic energy(turbine) > electrical energy

  -----------------------------------

  Impact on environment

  -water floods areas behind the dam killing plants and forcing animals to move

  -as fishes move,fishermen needs to relocate


  ☆Advantages

  Minimal greenhouse gases produced
• •Wind energy

  Kinetic energy(wind) > kinetic energy(wind turbine) > electrical energy(generator)

  -----------------------------------

  Impact on environment

  -large plots of land must be cleared and thus destruction of natural habitats hence potential loss of wildlife

  -birds may collide into turbines

  -noise pollution


  Advantages

  -minimal greenhouse gases produced
• ☆Geothermal energy

  Heat energy > kinetic energy(steam) > kinetic energy(turbine) > electrical energy

  -----------------------------------

  Impact on environment

  -large areas of land need to be cleared, destroying wildlife habitats and affecting diversity of species

  -traces of toxic elements may be drawn our from underground


  Advantages

  -minimal greenhouse gases produced
• ♡Biofuels

  Chemical potential energy > heat energy > kinetic energy

  -----------------------------------

  Impact on environment

  -Releases air pollutants when burnt


  Advantages

  -Plants used to make biofuels can ve grown in a short time(renewable)

  -Plants take in carbon dioxide during photosynthesis and this helps balance the amount of carbom dioxide released when biofuels are burnt
• Nuclear energy (non-renewable)°▪︎°

  Nuclear energy > heat energy > kinetic energy(steam) > kinetic energy(turbine) > electrical energy

  -----------------------------------

  Impact on environment

  -potential risk to health and safety of nearby communities

  -nuclear waste needs to be stored without leakage


  ☆Advantages☆

  -clean energy

  -less land required
• Fossil fuels advantages

  -cost effective

  -doesnt require as much land as solar or wind energy


  Solar energy advantages

  -does not release air pollutants when generating electricity
• ------------total energy------------

  -useful energy -energy transferred

  To the surroundings

  •~• (Eg. Heat,sound,light energy)
• -Temperature is a measure of how hot an object is-

  Instrument to measure temperature:

  Thermometer

  SI unit=Kelvin(K)
• Heat is transferred from a hotter object to a colder object
• Conduction

  -transfer if heat from one place to another with a physical movement of a medium

  ★when an object is heated, the particlescmove faster(more vigorously)

  -these particles collide with neighbouring particles and transfer the energy, causing them to move faster as well.
• Covection

  -tranfer of heat without a physical movement of a medium
• Expansion contraction

  -gains heat -lose heat

  -expand -contract

  -vol ⬆️ -vol ⬇️
• Bimetalic strip

  1. expands at different rates
  2. Which expands more
  3. Bends
  4. Open-circuit