Force

Force

a push or pull
1. described by its strength and direction in which it acts
  1. strength measured in SI unit: Newton (N)
net force: combination of all forces on object
1. balanced: equal forces on 1 object in opposite directions; no motion
  1. --><--=0 N Forces may cancel each other + produce no net force
2. unbalanced: results in a net force + cause change in object's motion
  1. -><---=5N Two forces can subtract to produce a net force in the direction of the larger force
  2. -->-->=10N Two forces can add tgh to produce a larger net force than either original force
types of forces
1. friction: 2 surfaces exert when they rub against each other
  1. the strength of the force of friction depends on
    1. how hard the surfaces push together
      1. friction increases if surfaces push hard against each other
    2. types of surfaces involved
      1. smooth surfaces produce less friction than rough surfaces
  2. types of friction
    1. static: acts on objects that are not moving; prevents from sliding/slipping
      1. to make an object move, you must exert a greater force than the static friction
    2. sliding(kinetic): when 2 solids surfaces slide over each other
    3. rolling: when an objects rolls across a surface
    4. fluid: when a solid object moves moves through a fluid
2. gravity: pulls objects towards each other
  1. law of universal gravitation: the force of gravity acts between all objects in the universe
  2. if mass increases, gravity increases
  3. if distance increases, gravity decreases
  4. weight: force of gravity on a person/object at the surface of a planet
  5. free fall: when gravity is the only force acting on an object
    1. all objects accelerate at same rate regardless of mass
      1. an object accelerates when gravity is unbalanced
  6. air resistance: upward force; type of fluid friction; happens to objects falling through the air
    1. objects with greater surface area=more air resistance=falls slower
      1. as object speeds up, air res. increases until upward force=downward force--> balanced forces so no acceleration; velocity remains constant
        terminal velocity: greatest velocity a falling object reaches; reached when air res.=weight of object
  7. projectile: object that is thrown
    1. when thrown at an upward angle, gravity reduces vertical velocity
      1. when upward motion stops, gravity pulls it back toward the ground
        from this point the object will fall at the same rate as any dropped object
  8. Newton's laws of motion
    1. first law(law of inertia)
      1. an object at rest will remain at rest
      2. an object moving at constant v will continue unless unbalanced force acts on it
      3. object won't move until a force acts on it
        inertia: tendency of an object to resist change in motion
        great mass=great inertia= great force required to change its motion
    2. second law
      1. acceleration=net force/mass; force=mass x acceleration
      2. to increase acceleration-->increase force-->decrease mass
      3. acceleration of object depends on mass of object and force applied
    3. third law
      1. every action has an equal and opposite force
        action-reaction pairs: when action force occurs(push on an object) the object pushes back on your feet w/ an equal but opposite force(reaction force)
        action and reaction forces don't cancel out bc they're acting on different objects
        it only cancels out when balanced force is exerted on the same object from different directions
        you can't always detect motion when paired forces are in motion
        if inertia is so great, small amount of acceleration would he hard to notice
        high momentum=harder to stop
        larger mass=more momentum
        momentum: mass X velocity (km*m/s); described by direction and quantity
        momentum is conserved when objects collide
        law of conservation of momentum: any group of objects remains the same or is conserved inless outside forces act on it
        collision with 2 moving objects: mm of each car decreases while the other increases.
        collision with one moving object: all momentum transfers form the moving object to the stationary to make it move
        collision with connected objects: move slower
        high velocity=high momentum(even if mass is little)
  9. gravity and motion
  10. factors affecting gravity

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