FORCE

FORCE

1. What is a Force?

   • Force = Push or Pull
     • When one object pushes or pulls another object, you say that the first object exerts a force on the second object
     • Newton = The strength of a force is measured in the SI unit
       • Named after English Scientist, Isaac Newton
     • Strength and direction of a force can be represented by an arrow
       • The arrow points in the direction of a force
         • The longer the arrow, the greater the force
   • A force is described by its strength and by the direction in which it acts

2. Combining Forces

   • Net Force
     • Combination of all forces acting on an object
     • Determines whether an object moves and in which direction it moves
   • Unbalanced Forces
     • When there is a net force acting on an object, the forces are unbalanced
     • Unbalanced Forces can cause an object to start moving, stop moving, or change direction
     • Unbalanced forces acting on an object result in a net force and cause a change in the object's motion
   • Balanced Forces
     • Equal forces acting on one object in opposite directions
     • Balanced forces are acting on an object do not change the object's motion

3. Friction

   • The force that two surfaces exert on each other when they rub against each other
   • Causes of Friction
     • The strength of the force of friction depends on two factors: how hard the surfaces push together and the types of surfaces involved
     • In general, smooth surfaces produce less friction than rough surfaces
     • When the irregularities of one surface come into contact with those of another, friction occurs
   • Static Fricton
     • Friction that acts on objects that are not moving
     • Because of static friction, you must use extra force to start the motion of stationary objects
   • Sliding Friction
     • Occurs when two solid surfaces slide over each other
   • Rolling Friction
     • When an object rolls across a surface, rolling friction occurs
   • Fluid Friction
     • Occurs when a solid object moves through a fluid

4. Gravity

   • Force that pulls objects toward each other
   • Universal Gravitation
     • Gravity acts everywhere in the universe, not just on Earth
     • Isaac Newton discovered this
     • Law of Universal Gravitation
       • States that the force of gravity acts between all objects in the universe
         • Any two objects in the universe, without exception, attract each other
   • Factors Affecting Gravity
     • Two factors affect the gravitational attraction between objects: mass and distance
       • Mass: a measure of the amount of matter in an object
         • The more mass an object has, the greater its gravitational pull
           • Gravitational force also depends on distance between the objects
   • Weight and Mass
     • Mass: measure of the amount of matter in an object
     • Weight: a measure of the amount of matter in an object
       • The force of gravity on a person or object at the surface of a planet
         • Weight depends on the strength of gravitational force but mass does not

5. Gravity and Motion

   • Free Fall
     • When the only force acting on an object is gravity
       • In free fall, the force of gravity is an unbalanced force, which causes an object to accelerate
   • Air Resistance
     • Objects falling through air experience a type of fluid friction called air resistance
     • Increases w/ velocity
       • Terminal Velocity: Greatest velocity a falling object reaches
   • Projectile Motion
     • Projectile: An object that is thrown