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Warmup Sept 17 th - Think

Warmup Sept 17 th - Think. You were kidnapped and knocked out. Some time later, you wake up in a dark warehouse. All there is in the room is a scale and a light, so you decide to weigh yourself. WOW!!! You gained a whole lot of weight last night…what happened?

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Warmup Sept 17 th - Think

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  1. Warmup Sept 17th - Think • You were kidnapped and knocked out. Some time later, you wake up in a dark warehouse. All there is in the room is a scale and a light, so you decide to weigh yourself. WOW!!! You gained a whole lot of weight last night…what happened? • You remember seeing alien figures in a dream-state, and realize you must be on another planet. Is the planet smaller or more massive than Earth?

  2. Weight and Mass… Fg = mg (formula for weight) Fg (weight) is the force an object has due to gravity Gravity on the Earth 9.8m/s2

  3. Weight and Mass… What’s the mass of my 893N ex-husband that just happens to be in my basement?

  4. Weight Problems! Fg=mg • What does a 60kg tool weigh? • What’s the mass of a crate of tools that weighs 234 N?

  5. Weight and mass: • What does a case of the new Chipotle Gatorade with a mass of 54.8kg weigh?

  6. What would a 60kg tool weigh: • On Mars (accel of gravity 3.7m/s2 )? • On Jupiter (accel of gravity 24.8m/s2 )?

  7. What planet are you on?You have a 4kg cat that weighs 14.4N

  8. Now it’s time for Newton’s 2nd Law • Newton’s 1st: Inertia. At rest, stay at rest; in motion, stay in motion. • Newton’s 2nd: What happens when a force acts on an object? • Acceleration.

  9. Newton’s Second Law:Force = mass x acceleration Force equals mass times acceleration. F=ma

  10. Newton’s Second Law: • The acceleration of an object is directly proportional to the force applied to the object, and inversely proportional to the mass. • -or – if F then A if M then A

  11. Calculate the Force How Do We?

  12. How? Like this: My 4 kg cat, Jeter, ran at our kitten Shadow with an acceleration of 3.0 m/s2. He didn’t stop. Poor little kitten! After suffering a mild concussion, we wondered….how much force did Jeter hit him with? Force = mass x acceleration, or… 4 x 3 = 12

  13. 12 what? Remember Force has its own special unit… 1kg x 1m/s2 = 1 newton (1N) F = ma Learn it. Live it. Love it.

  14. Force = mass(acceleration) 1. How much force is needed to push a lawnmower of 30 kg at 2.5 m/s2?

  15. 2. How much force must be applied to a bowling ball that has a mass of 5kg to achieve an acceleration of 25m/s2?

  16. 3. What is the mass of a baseball that has an acceleration of 125 m/s2 after a force of 44 Newtons has hit it?

  17. 4. What is the acceleration of a 22kg wolf that hits attacks a bear with a force of 400 Newtons?

  18. Now you practice!

  19. Without friction…

  20. FRICTION Friction - a force that opposes motion, or “pushes back” when two surfaces are touching. It’s always around and it affects everything.

  21. Without friction…

  22. FRICTION- works against you …..but it can be helpful! When do I want… • A lot of friction? • http://www.youtube.com/watch?v=yTKwS-J7qVE • A little bit of friction? • http://digg.com/video/the-science-of-figure-skating • http://www.nbclearn.com/olympics

  23. Friction types and parts… • There are three Basic Types of Friction • Static • Kinetic • Fluid

  24. Types of friction: 1) Static friction: Friction that resists the start of sliding motion between two objects at rest. Keeps things stopped

  25. Types of friction: 2) Kinetic friction: The force that opposes the movement of two surfaces that are in contact and moving over each other.To make something move, you just overcome static friction by pulling with a force larger than kinetic friction.

  26. Kinetic Friction: Sliding or Rolling

  27. Types of friction: 3) Fluid friction: The friction between layers of a fluid. 2 types- Liquid and Gas Liquid- water, oil etc. Gas - Air

  28. Types of friction: Described by viscosity. Viscosity – the “thickness” of a fluid. Low viscosity = “thin;” High viscosity = “thick” or “viscous.” The less viscous a fluid is, the easier it moves.

  29. Does Size Matter? I’m talking about Mass or surface area folks!

  30. Friction DOES depend upon: • 1. surface area in contact • 2. mass/gravity (weight) of object • 3. the texture of the surface

  31. Friction is cumulative • Small amounts of friction in a system add up to become a large amount of friction.

  32. Textbook friction…CHALLENGE

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