chapter 9 science

• typhoon - a powerful storm with strong winds and heavy rain

  : force of the wind damages property

  : heavy rainfall causes flood

  : floodwaters exert forces on soil, loosens it -> landslide
• volcanic eruption

  : hot liquid rock (magma) exerts force on the earth's crust

  : too much pressure -> forced upward to the surface

  : released as heat, light, kinetic energy
• earthquakes

  : plates (in the earth's crust) push against each other with great force, release of energy
• tsunami - series of large, powerful ocean waves, often caused by a powerful earthquake under the ocean
• force - a push or pull interaction between objects that result in a change in the state of rest or motion of a body

  : contact force (friction)

  : non-contact force (gravity)
• frictional force - occurs when two solid surfaces are in contact
• reducing friction

  : smooth surfaces

  : lubrication (oil)

  : streamlining shape (airplane)
• disadvantages of friction

  : makes movement more difficult

  : wears away materials

  : produces unwanted heat
• advantages of friction

  : holds nail in place

  : bicycle brakes

  : walk

  : prevents slipping
• gravitational force - attractive force that exists between any two objects
• electrostatic force

  : unlike charges attract

  : like charges repel

  : electrostatic force of attraction/repulsion
• magnetic force - force exerted by a magnet on a magnetic material
• weight - gravitational force acting on an object

  : measured in newtons (N)

  : mass x gravitational field strength (m x g)
• measure mass -> beam balance

  measure weight -> spring balance
• effects of forces

  1. start an object moving
  2. stop moving object
  3. change speed of moving object
  4. change direction of moving object
  5. turning effect
  6. change in size/shape
  7. change in pressure
• speed - distance travelled per unit time

  : SI unit -> metre per second (m/s)
• turning effect

  : produces a turning effect about a fixed point (pivot)
• pressure - amount of force acting per unit area

  : SI unit -> pascal (Pa)

  : used in calculations -> newton per square metre (N/m^2)
• pressure increases when

  : applied force increases

  : contact area decreases
• pressure in liquids

  : more depth, more pressure

  : dam, submarine
• atmospheric (air) pressure

  _straw

  : suck out the air, air pressure decreases

  : air pressure outside the straw is greater

  _suction cup

  : press on the suction cup

  : less air inside, air pressure inside decreases

  : pressure outside is greater, force holds the cup to the surface
• work done - force exerted on an object and the object moves in the direction of the force applied

  : SI unit -> joule (J)

  : work done = force x distance
• for work to be done,

  1. force must be applied
  2. object must move
  3. object moves in the same direction

  (yes to all)
• energy - ability to do work or to produce a change

  : always converted from one form to another, never created or destroyed
• calculate weight

  : mass x gravitational field strength

  [convert to g to kg first]

  • g is always 10N/kg on earth

  calculate speed

  : distance x time

  [SI unit -> m/s]

  
  

  calculate pressure

  : force/area

  [convert to m first!!]

  • Pa or N/m2

  calculate work done

  : force (weight) x distance

  [convert to m]