3'2 Weight, Gravity, and Friction

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3.2 Weight, Gravity, and Friction

• Unit 1 Chapter 3
• CPO Science
• Courtney Lewis
• Stapley Junior High School

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Gravity

• If you and a friend are at the top of a hill and
  you both start going down at the same time with
  the same force, will you both reach the bottom at
  the same time?
• Force that pulls every mass toward every other
  mass
• Depends on massthe bigger the mass, the bigger
  the gravitational pull

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Mass Weight

• Weight is force due to GRAVITY
• If you know mass, use a9.8 m/s2 to find the
  weight (in other words the force)
• We use the equation
• Fwmg (g is the acceleration due to gravity)
• Read it F sub w equals mass times acceleration
  due to gravity
• N for weight kg for mass

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Newtons law of universal gravity

• Gravity a force of attraction that exists between
  any 2 objects that have mass
• The law The force of attraction between 2
  objects is directly related to the masses of the
  objects inversely related to the distance
  between them

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Equation of Universal Gravitation
2 bowling balls, one is 20 kg the other is 30 kg
and they are 10 m apart, what is the
gravitational force between the two bowling balls?
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Friction

• Forces that result from relative motion between
  objects, opposes motion
• Types of Friction
• Air Frictionair moving around moving objects
• Sliding Friction2 surfaces rub together
• Viscous Friction2 fluids slide against each
  other
• Rolling Friction1 object rolls over another

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Friction Motion

• Friction is opposite the force causing motion
• Force in Fma is the net force, the gravitational
  forcefriction
• Friction slows acceleration
• Use better designs to try to reduce friction to
  make machines more efficient

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Homework

• Assignment 3.2 p. 62 Vocab Set 23, CR 711,
  Problems 24
• DUE Wednesday, May 7, 2008