1.  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? WARMUP SEPT 17 TH - THINK

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/s 2

3. WEIGHT AND MASS… What’s the mass of my 893N ex-husband that just happens to be in my basement?

4. WEIGHT PROBLEMS! F G =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/s 2 )?  On Jupiter (accel of gravity 24.8m/s 2 )?

7. WHAT PLANET ARE YOU ON? YOU HAVE A 4KG CAT THAT WEIGHS 14.4N Planet Gravity : (m/s 2 ) a= Mercury3.61 Venus8.83 Earth9.8 Earth's Moon1.6 Mars3.75 Jupiter26 Jupiter's Moon Io1.81 Saturn11.2 Uranus10.5 Neptune13.3 Pluto0.61

8. NOW IT’S TIME FOR NEWTON’S 2 ND LAW  Newton’s 1 st : Inertia. At rest, stay at rest; in motion, stay in motion.  Newton’s 2 nd : 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

11. 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

12. CALCULATE THE FORCE HOW DO WE?

13. HOW? LIKE THIS: My 4 kg cat, Jeter, ran at our kitten Shadow with an acceleration of 3.0 m/s 2. 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

14. 12 WHAT? Remember Force has its own special unit… 1kg x 1m/s 2 = 1 newton (1N) F = ma Learn it. Live it. Love it.

15. FORCE = MASS(ACCELERATION) 1. How much force is needed to push a lawnmower of 30 kg at 2.5 m/s 2 ?

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

17. 3. What is the mass of a baseball that has an acceleration of 125 m/s 2 after a force of 44 Newtons has hit it?

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

19. NOW YOU PRACTICE!

21. WITHOUT FRICTION…

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

23. WITHOUT FRICTION…

24. FRICTION- WORKS AGAINST YOU …..BUT IT CAN BE HELPFUL! WHEN DO I WANT…  A lot of friction? A lot of friction?  http://www.youtube.com/watch?v=yTKwS-J7qVE http://www.youtube.com/watch?v=yTKwS-J7qVE  A little bit of friction? A little bit of friction?  http://digg.com/video/the-science-of-figure-skating http://digg.com/video/the-science-of-figure-skating  http://www.nbclearn.com/olympics http://www.nbclearn.com/olympics

25. FRICTION TYPES AND PARTS…  There are three Basic Types of Friction  Static  Kinetic  Fluid

26. TYPES OF FRICTION: 1) Static friction: Friction that resists the start of sliding motion between two objects at rest. Keeps things stopped

27. 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.

28. KINETIC FRICTION: Sliding or Rolling

29. TYPES OF FRICTION: 3) Fluid friction: The friction between layers of a fluid. 2 types- Liquid and Gas Liquid- water, oil etc. Gas - Air

30. 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.

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

33. FRICTION IS CUMULATIVE  Small amounts of friction in a system add up to become a large amount of friction.

34. TEXTBOOK FRICTION…CHALLENGE