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Force

Force. Definition: A push or a pull Force can cause motion SI unit -> Newton (N)= 1 kg x 1 m/s 2 Sometimes pound ( lb ) can be used as a unit for force 1 Newton=0.22481 pounds force. Combining Forces. Balanced Force Equal and opposite forces = ‘balanced’

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Force

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  1. Force Definition: • A push or a pull • Force can cause motion • SI unit -> Newton (N)= 1 kg x 1 m/s2 • Sometimes pound (lb) can be used as a unit for force • 1 Newton=0.22481 pounds force

  2. Combining Forces • Balanced Force • Equal and opposite forces = ‘balanced’ • Balanced forces give no motion No motion of hands

  3. Combining Forces • Unbalanced force – more force in one direction (net force)

  4. Net Force • Bigger force to the right • Smaller force to the left • Net force to the right

  5. III. Friction and Gravity • Friction – a force that opposes motion • Caused by the interaction between two touching surfaces rubbing against each other • Four Types

  6. a. Static • Friction that acts on something that is not moving • No heat or wear is generated

  7. b. Sliding • Force resulting when pushing or pulling an object over a surface.

  8. c. Rolling • Contact is reduced because of rollers or wheels or ball bearings.

  9. d. Fluid friction • Resistance from a “fluid” • Fluids are liquids and gases.

  10. Reducing friction • A smooth surface does not demonstrate as much friction as a rough surface. • Waxing, oiling, etc. can be used to reduce friction.

  11. Coefficient of Friction • µ= “coefficient of friction”  represents the roughness of the surfaces in contact. • In reality there two main subtypes: • µs- Static friction to get it moving • µk- Kinetic friction to keep it moving • µs> µk needed for movement to occur

  12. Gravity – force of attraction between two objects ---> pulling force Factors Affecting Gravity • Mass – more mass, more gravity • Distance – closer, more gravity http://www.exploratorium.edu/ronh/weight/

  13. End Check- Complete on separate sheet of paper • 1. Describe three ways in which a car’s velocity will change • 2. Identify a one situation involving unbalanced force and one situation involving balanced force. Explain how it each affect the motion of an object. • 3. Arrange the following pairs of surfaces in order of most friction to least friction • A shoe sole and a waxed basketball court • A shoe sole and the frozen surface of a lake • A shoe sole and the sidewalk

  14. End Check- Complete on separate sheet of paper • 4. Explain why Venus, which is slightly less massive than Earth, experiences a stronger gravitational pull from the sun than Earth does. • 5. What is the average acceleration of a scooter that starts at rest and moves straight ahead at 12 m/s in 24 s. • 6. Which will be moving faster after 3.0 s, a cyclist maintaining a constant velocity of 15 m/s straight ahead or a race car accelerating forward from a stoplight at 4.0 m/s2?

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