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Warm Up February 27, 2013

Warm Up February 27, 2013. Two friends are discussing what the world would be like if there were no friction. Emily says, “To go to school in the morning, I could just push off my front door and I could slide all the way to school.”

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Warm Up February 27, 2013

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  1. Warm Up February 27, 2013 • Two friends are discussing what the world would be like if there were no friction. • Emily says, “To go to school in the morning, I could just push off my front door and I could slide all the way to school.” • Anna says, “No, I don’t think so. You would eventually slow down after a while.” Who do you agree with most and why?

  2. Center of Gravity Test • Can you lift up the chair without moving your feet???

  3. 10.2 Gravity • Gravity – an attractive force that pulls objects that have mass together. • F = force of gravity • G = gravitational constant • m1 and m2 = masses of 1 and 2 • d = distance between mass 1 and 2

  4. The more massive an object is, the greater its gravitational force. • The sun is the most massive thing in our solar system which is why the planets orbit around it.

  5. So why aren’t we pulled toward the sun?? • Well, the sun is more massive than earth, but it is also much further away. Earth is much closer to us and also very massive, so we feel its gravitational pull more strongly.

  6. This is a modern way that physicists envision gravity. • They see gravity as a change in the shape of space-time.

  7. Weight • Weight – a force exerted on objects near planets. Weight = mass x acceleration due to gravity On earth, acceleration due to gravity is 9.8 m/s2 • Weight is measured in pounds or Newtons because it is a force.

  8. Fundamental Forces • Gravity – pulls objects with mass together • Electromagnetic Force – pulls opposites together and pushes like charges apart • Strong Force – pulls protons together in the nucleus • Weak Force - pushes protons, neutrons and electrons out of the nucleus (radioactive decay)

  9. You can become weightless but you can never become massless! • If gravity is not pulling on you, will have no weight. In other words, if you stood on a scale, it would read 0.

  10. Vomit Comet

  11. Free Fall • If something is falling straight down, without any downward pull other than gravity, it is in free fall. • Objects in free fall all accelerate at the same rate, earth’s acceleration due to gravity, which is 9.8 m/s2.

  12. Try this: • Start with 2 pieces of paper. • Crumple one into a ball. • Drop both from the same height. Note which one hits the ground first.

  13. The force of gravity acting on both pieces of paper is the same. • BUT, the net force is not the same!! • The uncrumpled paper has to “push through” more air molecules, which exert a greater upward force on this paper. This upward force is a type of fluid friction called air resistance.

  14. Earth Moon

  15. Demo

  16. Projectile Motion • The pull of gravity acts independently of horizontal motion. • Objects in free fall experience the same acceleration due to gravity as projectiles do.

  17. Agenda • Warm Up • Review HW • Bill Nye “Gravity” • 10.2 Gravity Notes • Cool Down

  18. Cool Down • Title: Gravity Circle Map • P. 388 #2a-c and #3a-c • 10.2 Vocab Booklet (7 words on p. 380 “mass-tension”) Homework

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