Physics

• What is mass measured in?

  Kilograms
• What causes weight to act downwards?

  Weight is due to an object having mass in a gravitational field
• What is tension due to?

  Contact pull
• In which direction does tension act?

  Tension acts in any direction
• What causes friction?

  Friction is due to an object moving past another object in contact with it
• How is friction measured?

  In newtons
• What are the two types of friction?

  Dynamic and static friction
• What does friction depend on?

  Surface and normal contact force N
• In which direction does friction always act?

  Opposite to the direction of potential motion
• What is the law for friction?

  • Area of contact does not affect frictional force
  • Dynamic force: $F =$$\mu_d \times N$
  • Dynamic friction does not depend on speed of sliding
  • Static force: $F =$$\mu_s \times N$
  • $\mu_s > \mu_d$
• What are drag and air resistance examples of?

  Friction due to an object moving through a fluid
• In which direction do drag and air resistance act?

  Opposite to the direction of movement
• What is normal contact force due to?

  Another object in contact pushing the first
• In which direction does normal contact force act?

  Perpendicular to the surface of the second object
• What is upthrust (buoyancy effect) due to?


  The displacement of a fluid caused by weight
• In which direction does upthrust act?

  Opposite to gravity
• What causes gas pressure?

  Particles in the fluid colliding with the object
• In which direction does gas pressure act?

  Perpendicular to the object's surface
• What causes lift?

  A difference of pressure
• In which direction does lift act?

  From high pressure to low pressure
• What do electric and magnetic forces act on?

  Charged particles or magnetic material
• How do electric and magnetic forces act?

  They can either attract or repel
• What is Hooke's Law?


  Restoring force equals spring constant times extension
• What is the formula for Hooke's Law?

  $F =$$k \times x$
• What is momentum defined as?

  Mass times velocity
• Why is momentum considered a vector?

  Because it has both magnitude and direction
• What is the principle of conservation of momentum?

  • In a closed system with no external forces, total momentum remains constant
  • Momentum before = Momentum after
• What should you consider if momentum before equals zero but momentum after has objects moving?

  They must move in different directions to cancel out
• What can change in momentum be written as?

  Impulse J