FORCE

FORCE

What is force
1. A push or a pull
2. Described by its strengh and by the direction in which it acts
3. A projectile
  1. When you throw a projectile at an upward angle, the force of gravity reduces its vertical velocity
    1. Eventually the upward motion of the projictile will stop and gravity will pull it back toward the ground
      1. From this point the projectile will fall at the same rate as any dropped object
  2. An object that is thrown
  3. If two balls are thworn one horizontally and one vertically
    1. Gravity acts the same way on both
      1. So both fall at the same rate
        And will hit the ground at exactly the same time
Types of forces
1. Net force
  1. When more than a single force acts on an object at one time
  2. It is the combination of all forces acting on a object
  3. It determines wheter an object moves and also in which direction it moves
2. Two kinds
  1. Unbalanced forces
    1. Result in a net force and cause a change in the object's motion
      1. It can cause on object to start, stop moving or change direction
    2. Whenever there is a net force acting on a object, the forces are unbalanced
  2. Balanced forces
    1. Do not changethe object's motion
      1. There is no net force
3. Gravity
  1. A force that pulls objects towards each other
  2. Law of Universal Gavitation
    1. States that the force of gravity acts between all objects in the universe
      1. Any two objects in the universe, without exception, attract each other
  3. Gravitational attractuion depends on
    1. Mass
    2. Distance
    3. Gravity increases with mass and dicreases with distance
  4. On earth, gravity is a downward force that affects all objects
  5. Free fall
    1. When the only force acting on an object is gravity the object is said to be in free fall
    2. In free fall, the force of gravity is an unbalanced force
      1. Causes an object to accelerate
        At a rate of 9.8 m/s
        All object in free fall accelerate at the same rate regradless of their massess
4. Friction
  1. Four kinds
    1. Fluid
      1. Occurs when a solid moves through a fluid
      2. Air resistance
        Objects falling through air experience a type of fluid friction called air resistance
        Upward force exerted on falling objects
        Not the same for all objects
        Greater surface = more air resistance
        In a vacum where there is no air, all objects fall with exactly the same rate of acceleration
        Increases with velocity
        Until it reaches Terminal velocity
        Greatest velocity a falling object reaches
        Reached when the force of air resistance equals the weight of the object
        Forces become balanced
        No more acceleration
        The object continues to fall but its velocity remains constant
    2. Sliding
      1. Occurs when two solid surfaces slide over each other
    3. Rolling
      1. occurs when an object rolls across a surface
    4. Static
      1. Acts on objects not moving
      2. Because of it, you must use an extra force greater than static friction to start the motion of stationary objects
        Once the object is moving, there is no longer static friction
        Other types take over
  2. The force that two surfaces exert on each other when they rub against each other
  3. The strengh of the force of friction depends on
    1. how hard the surfaces push together
    2. types of surfaces involved
  4. Friction always acts in a direction opposie to the direction of the object's motion
  5. Rolling and fluid friction is easier to overcome than sliding friction
How is it measured
1. Force
  1. When arrows are used
    1. When forces act in the same direction, they combine by the addition of their individual forces
    2. When forces act in opposite directions, they combine by the substraction of their individual forces
      1. The net force always acts in the direction of the greater force
      2. If the opposing forces are of equal strengh, there is no net force.
        There is no change in he object's motion
    3. In order to find net force
  2. In Newton (N)
    1. SI unit
2. Weight and Mass
  1. Mass is a measure of the amount of matter in a object
  2. The force of gravity on a person or object at the surface of a planet is known as weight
    1. Weight is a measure of the gravitational force exerted on it
  3. Weight varies with the strengh of the gravitational force but mass doesn't
How is it represented
1. With an arrow
  1. The arrow points in the direction of a force
  2. The length of the arrow tells you the strengh of a force
    1. Longer = greater

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