TOPIC 9 -FORCES AND THEIR EFFECTS

• when 2 objects interact they both experience a force
• touching = contact force
• not-touching = non-contact force
• Friction?


  Force that acts to resist 2 objects sliding past each other
• VECTORS ARE REPRESENTED WITH ARROWS

  • length of arrows= magnitude of vectors
  • direction of arrows = direction of vector
• action-reaction forces

  • these forces are pairs with same type of force and same size but act in opposite direction
• Contact forces:

  • ONLY occurs between 2 objects touching
  • includes normal contact force and friction
  • normal contact force(always acts at right angle to surface between 2 objects)
• contact force created when one object pushes against another
• mechanical procceses are wasteful when they cause rise in tempature because energy is dissipated(wasted) in heating the surroundings
• all mechanical process induce surfaces moving past each other so some thermal energy is dissipated due to friction
• what are non contact forces?


  Gravity(non-uniform), magnetic force(non-uniform), and electric field-plates(uniform) and point charges(non-)
• How does Lubrication prevent energy being wasted

  lubrication is spreading oily substances over parts of mechanical system which reduces friction between objects when they move, so more energy is transferred into useful kinetic energy stores then less energy is transferred into thermal energy stores.
• physical quantities are scalars or vectors
• scalar(magnitude,size) examples:

  • energy
  • mass
  • length
  • speed
  • density
• vector(magnitude and direction) examples:

  • displacement
  • velocity
  • all forces
  • momentum
  • acceleration
• forces are either unbalanced or equilibrium
• what is equilibrium


  if forces acting on object are balanced
• balanced forces= equilibrium = zero resultant force
• equilibrium means objects aren't accelerating or decelerating
• unbalanced - this force cause acceleration or deceleration
• resultant force is the sum of all forces
• forces in same direction = add
• forces in opposite direction = subtract
• force at right angle can be separated into 2 forces at right angle to each other then added
• What is free body diagram?


  shows direction and magnitude of force on object
• often objects in diagram shown as dot or box
• arrows in free body diagram show which force is bigger
• Zero resultant force:

  • arrows cancel each other out
  • don't balance
  • This means object is travelling at constant speed or not moving
• forces in diagram include

  • normal contact force, weight, friction,drag,upthrust
• Non-contact force applies force a distance and have force fields
• What are these: friction, thrust, push and pull, air resistance, water resistance,normal reaction force 


  Contact force
• What objects are affected by gravitational field


  Objects with mass
• If force is non-uniform what does this mean

  1)force acts in different direction

  2)field gets weaker as we move from surface
• If field lines gets further apart means it getting weaker
• Electrical field affects anything with charge

  What ate the 2 types

  Plates, point charges
• If force is uniform(same) what does this mean?


  Same direction everywhere, same strength everywhere
• Magnetic field exerts force on magnetic material what are they


  Iron, colbat, nickel

  
• positive arrows go out and.... (electrical fields)


  Negative arrows go in

  
• What objects are affected by gravitational field
 


  Objects with mass

  
• On point charges if attract field lines go in if repel


  Field lines push out