FORCE

FORCE

1. What is force

   • A push or a pull
   • Described by its strengh and by the direction in which it acts
   • A projectile
     • When you throw a projectile at an upward angle, the force of gravity reduces its vertical velocity
       • Eventually the upward motion of the projictile will stop and gravity will pull it back toward the ground
         • From this point the projectile will fall at the same rate as any dropped object
     • An object that is thrown
     • If two balls are thworn one horizontally and one vertically
       • Gravity acts the same way on both
         • So both fall at the same rate
           • And will hit the ground at exactly the same time

2. Types of forces

   • Net force
     • When more than a single force acts on an object at one time
     • It is the combination of all forces acting on a object
     • It determines wheter an object moves and also in which direction it moves
   • Two kinds
     • Unbalanced forces
       • Result in a net force and cause a change in the object's motion
         • It can cause on object to start, stop moving or change direction
       • Whenever there is a net force acting on a object, the forces are unbalanced
     • Balanced forces
       • Do not changethe object's motion
         • There is no net force
   • Gravity
     • A force that pulls objects towards each other
     • Law of Universal Gavitation
       • States that the force of gravity acts between all objects in the universe
         • Any two objects in the universe, without exception, attract each other
     • Gravitational attractuion depends on
       • Mass
       • Distance
       • Gravity increases with mass and dicreases with distance
     • On earth, gravity is a downward force that affects all objects
     • Free fall
       • When the only force acting on an object is gravity the object is said to be in free fall
       • In free fall, the force of gravity is an unbalanced force
         • 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
   • Friction
     • Four kinds
       • Fluid
         • Occurs when a solid moves through a fluid
         • 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
       • Sliding
         • Occurs when two solid surfaces slide over each other
       • Rolling
         • occurs when an object rolls across a surface
       • Static
         • Acts on objects not moving
         • 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
     • The force that two surfaces exert on each other when they rub against each other
     • The strengh of the force of friction depends on
       • how hard the surfaces push together
       • types of surfaces involved
     • Friction always acts in a direction opposie to the direction of the object's motion
     • Rolling and fluid friction is easier to overcome than sliding friction

3. How is it measured

   • Force
     • When arrows are used
       • When forces act in the same direction, they combine by the addition of their individual forces
       • When forces act in opposite directions, they combine by the substraction of their individual forces
         • The net force always acts in the direction of the greater force
         • If the opposing forces are of equal strengh, there is no net force.
           • There is no change in he object's motion
       • In order to find net force
     • In Newton (N)
       • SI unit
   • Weight and Mass
     • Mass is a measure of the amount of matter in a object
     • The force of gravity on a person or object at the surface of a planet is known as weight
       • Weight is a measure of the gravitational force exerted on it
     • Weight varies with the strengh of the gravitational force but mass doesn't

4. How is it represented

   • With an arrow
     • The arrow points in the direction of a force
     • The length of the arrow tells you the strengh of a force
       • Longer = greater