current_chp._10-2

							                        Friction Foldable
•   Once your paper is folded, label the four sections with
    the four types of friction:
      1.   Static friction
      2.   Sliding friction
      3.   Fluid friction
      4.   Rolling friction
      p. 342
                       Types of friction
• Static friction – friction that acts on objects that are not moving
  Ex. Pushing on a heavy refrigerator/ driving off with a book on
  top of the car

• Sliding friction – friction that occurs when 2 solid surfaces slide
  over each other Ex. Bike brakes/ ballet dancers
                 Types of Friction (cont’d)

• Rolling friction- occurs when an object rolls across a surface
  (ex: skateboard on road)

• Fluid friction – occurs when a solid object moves through a
  fluid          (ex: surfboard on water)
              Bell Ringer          1-25-11

See if you can answer these from memory:
1. What is a force?
2. What unit measures force?
3. A ________ is a combination of all the forces acting on an
      object.
4. List the two types of forces and the key words we use to
      remember them.
Chapter 10
 section 2

  Gravity
      Who is this?

Issac Newton- He came up
 with the Law of Universal
        Gravitation.
                                 Gravity

• Gravity- a force that pulls objects toward each other
    – Ex: Earth pulling us toward it
• Law of Universal Gravitation- the law that states that the force of
  gravity acts between all objects in the universe
• Why don’t you feel the gravity between other objects and you?
                                  Gravity
• Two factors affect Gravity:
   – 1. Mass
       •   amount of matter in an object
       •   Not affected by gravity
       •   Greater the mass, greater the gravity
       •   Ex: sun and planets
   – 2. Distance
       • Greater the distance, Less the gravity
                          Weight

• Weight- the force of gravity on an object or person
                           Free Fall

• Free fall- an object is in free fall when there is only one
  force (gravity) acting on the object
                        Air Resistance

•   Air Resistance- an upward force exerted on falling objects
•   It’s not the same for all objects.
•   The greater the surface area, the greater the air resistance.
•   Another name for air resistance is drag.
                            Terminal Velocity
• Terminal Velocity- the greatest velocity a falling object
  reaches
   – Exists when the force of air resistance equals the weight of
     the object/or the force of gravity pulling down on the object
   – Air Resistance = Weight or Gravity
                         Projectile
• Projectile- an object that is thrown

• Will an object that is thrown horizontally land on the
  ground at the same time as an object that is dropped?
                  Video
• Terminal Velocity
                Exit Quiz              1-26-10
1. What is a force?
2. The combination of all the forces acting on an object is called
   ______.
3. If two forces are balanced, is there a net force?
4. The SI unit for force is the ________.
5. Tell me one of the four types of friction and give an example.