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3.2 Weight, Gravity, and Friction

3.2 Weight, Gravity, and Friction. Unit 1 Chapter 3 CPO Science Courtney Lewis Stapley Junior High School. 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?

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3.2 Weight, Gravity, and Friction

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  1. 3.2 Weight, Gravity, and Friction Unit 1 Chapter 3 CPO Science Courtney Lewis Stapley Junior High School

  2. 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 mass—the bigger the mass, the bigger the gravitational pull

  3. Mass & Weight • Weight is force due to GRAVITY • If you know mass, use a=9.8 m/s2 to find the weight (in other words the force) • We use the equation: • Fw=mg (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

  4. Newton’s 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

  5. 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?

  6. Friction • Forces that result from relative motion between objects, opposes motion • Types of Friction: • Air Friction—air moving around moving objects • Sliding Friction—2 surfaces rub together • Viscous Friction—2 fluids slide against each other • Rolling Friction—1 object rolls over another

  7. Friction & Motion • Friction is opposite the force causing motion • Force in F=ma is the net force, the gravitational force—friction • Friction slows acceleration • Use better designs to try to reduce friction to make machines more efficient

  8. Homework • Assignment 3.2 p. 62: Vocab Set 2—3, CR 7—11, Problems 2—4 • DUE Tuesday, May 12, 2009

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