Force

Force

1. a push or pull

   • described by its strength and direction in which it acts
     • strength measured in SI unit: Newton (N)

2. net force: combination of all forces on object

   • balanced: equal forces on 1 object in opposite directions; no motion
     • --><--=0 N Forces may cancel each other + produce no net force
   • unbalanced: results in a net force + cause change in object's motion
     • -><---=5N Two forces can subtract to produce a net force in the direction of the larger force
     • -->-->=10N Two forces can add tgh to produce a larger net force than either original force

3. types of forces

   • friction: 2 surfaces exert when they rub against each other
     • the strength of the force of friction depends on
       • how hard the surfaces push together
         • friction increases if surfaces push hard against each other
       • types of surfaces involved
         • smooth surfaces produce less friction than rough surfaces
     • types of friction
       • static: acts on objects that are not moving; prevents from sliding/slipping
         • to make an object move, you must exert a greater force than the static friction
       • sliding(kinetic): when 2 solids surfaces slide over each other
       • rolling: when an objects rolls across a surface
       • fluid: when a solid object moves moves through a fluid
   • gravity: pulls objects towards each other
     • law of universal gravitation: the force of gravity acts between all objects in the universe
     • if mass increases, gravity increases
     • if distance increases, gravity decreases
     • weight: force of gravity on a person/object at the surface of a planet
     • free fall: when gravity is the only force acting on an object
       • all objects accelerate at same rate regardless of mass
         • an object accelerates when gravity is unbalanced
     • air resistance: upward force; type of fluid friction; happens to objects falling through the air
       • objects with greater surface area=more air resistance=falls slower
         • 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
     • projectile: object that is thrown
       • when thrown at an upward angle, gravity reduces vertical velocity
         • 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
     • Newton's laws of motion
       • first law(law of inertia)
         • an object at rest will remain at rest
         • an object moving at constant v will continue unless unbalanced force acts on it
         • 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
       • second law
         • acceleration=net force/mass; force=mass x acceleration
         • to increase acceleration-->increase force-->decrease mass
         • acceleration of object depends on mass of object and force applied
       • third law
         • 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)
     • gravity and motion
     • factors affecting gravity

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