# current_chp._10-2 by wanghonghx

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```									                        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.

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