Forces

• Forces in nature

  Have the ability to destroy but also have the ability to create beautiful land forms
• How do forces in Nature affect us?

  1. Earthquakes

  2. Tsunamis

  3. Volcanic eruptions

  4. Hurricanes
• Types of forces

  Contact force

  Non-contact force
• Friction


  • A type of force that opposes motion
  • Exists between the surfaces of two objects in contact
• Magnetic force


  • The push or pull between magnets only or magnets on magnetic materials

  
• Gravitational force


  • It is the force acting on an object due to gravity and attracts objects to planets
• Weight

  When a planet exerts gravitational force on another object, it pulls it towards its centre
• Ocean tides


  The tides on Earth are caused partly by the moon's gravity pulling on the waters of the oceans
• Mass


  The measure of the amount of matter in an object
• Weight


  The gravitational force acting on an object
• Mass is the same


  Weight is different on Earth and Moon
• Changes due to forces

  1. Move stationary object

  2. Change speed of object

  3. Change direction of a moving object

  4. Stop a moving object

  5. Turning effect is produced when a force applied causes an object to rotate about a specific point (pivot)
• Turning effect


  A turning effect is produced when a force applied causes an object to rotate about a specific point or axis (lever)
• The greater the distance between the force applied and the pivot


  The greater the turning effect of the applied force
• Free-body diagram (FBD)

  Shows all the forces acting on an object (or a body) in a specific scenario
• The skydiver falls with constant speed because the total upward force (air resistance) is equal to the total downward force (weight) acting on the object. Therefore the speed of the skydiver does not increase.
• Normal force


  Supporting force for weight from the surface. Ensuring the downward force (weight of the object) is balanced out.
• Pressure


  The force acting perpendicularly per unit contact area
• When a greater contact area of an object, the pressure exerted by the object is smaller. (vice versa)
• Atmospheric pressure


  The weight of air pushing down on a given area on Earth
• As depth in a liquid increases


  The liquid pressure increases
• Work

  When work is done on an object, energy is converted from one form to another
• SI unit for work

  Joules (J)
• Larger units for work

  Kilojoules (kJ)
• Pressure


  As pressure increases, liquid travels further out of the container
• Liquid pressure


  The greater the depth of liquid, the greater the liquid pressure
• Drinking from a straw

  1. Air is removed from the straw

  2. Air pressure decreases in the straw

  3. Higher air pressure outside the straw pushes more liquid into the straw
• Suction cup


  1. Air inside the suction cap is removed

  2. Air pressure decreases inside

  3. Atmospheric pressure outside is greater, causing the cap to "suck" onto the surface
• Work

  When work is done on an object, energy is converted from one form to another<|>SI unit for work is joules (J)<|>Larger units are measured in kilojoules (kJ)<|>1 kJ = 1000 J
• For work to be done

  • There is a force acting on the object
  • The object moves
  • The movement of the object is in the direction of the force
• Boy pushing against a solid wall does work, but a girl holding a heavy pile of books in a stationary position does no work
• Calculating work done


  • Marie lifts a 5 kg mass 1 m high (50 J)
  • Isaac carries an 8 kg pail of water up 15 steps, each 20 cm high (240 J)
  • Pulling up a 1 N bucket with 23 N of water for 170 m (4080 J)
  • Marie carries her 20 N bag 30 m (no work done)
• Energy


  The ability to do work<|>Unit is joule (J) or kilojoule (kJ)
• Types of energy


  • Potential Energy
  • Kinetic Energy
  • Light Energy
  • Electrical Energy
  • Sound Energy
  • Heat Energy
• Energy conversions in a skate ramp

  1. No friction: GPE maximum at top, KE maximum at bottom, total energy constant

  2. With friction: GPE and KE never equal, total energy decreases
• In a frictionless scenario, the total energy of a situation is conserved
• In a scenario with friction, the total energy decreases due to energy dissipation
• An object at a higher height will have greater GPE
• An object moving faster will have greater Kinetic Energy
• Law of conservation of energy


  Energy cannot be created or destroyed, it can only be converted from one form to another