Gravity, Friction and Simple Machines

1. Gravity, Friction and Simple Machines BY: BRIANNA SHIELDS

2. Do Now • 1. Which of Newton’s laws of motion explains inertia? • 2. Which type of atomic particle moves during static and current electricity? • 3. Which property of light allows it to bend as it passes through various types of matter?

3. GOAL • To relate gravity and weight • To define friction and air resistance and design ways to increase it or decrease it • To define work • To describe various simple machines

4. Gravity 1. Force of attraction-pulls things downward 2. Objects fall at a rate= 9.8 m/s2 acceleration due to gravity

6. Example 1 sec After falling for 7 seconds what is the acceleration of the ball? 2 sec 3 sec 4 sec 5 sec Speed of a falling object V = 9.8 x t (V= a(g) x t ) 6 sec 7 sec

7. Free Fall

8. Terminal Velocity Object no longer accelerates- it travels at a constant speed

9. Law of Universal Gravitation 1. All objects have gravity 2. Massive objects = greater gravity 3. Objects close together= more gravitational attraction

10. More Gravity Less Gravity Less Gravity More Gravity

11. Weight 1. Amount of gravity that pulls on an object Closer to core = more gravitational pull 2. Weight changes with location WEBSITE: Your weight on other worlds

12. Weight 3. W= m x 9.8 Weight= mass x acceleration due to gravity

13. Weight Calculations • What would a 10kg book weigh in newtons? • W = ma = 10kg x 9.8 m/s^2 = ? • What would a 50kg person weigh in newtons? • W = ma= 50kg x 9.8 m/s^’2 = ?

14. If a feather and a hammer are dropped at the same time, which will hit the ground first?

15. Air resistance Prevents objects from falling at 9.8 m/s Slows objects down Object rubs against air molecules Pushes upward on objects Due to object’s shape Why does the hammer hit the ground before the feather?

16. If a feather and a hammer are dropped at the same time on the moon, which will hit the ground first? Find out by watching “Brain Bytes” NASA Vodcast

17. Friction 1. Exists Where 2 surfaces touch 2. Acts in direction opposite to object’s motion

18. Friction acting on an incline • Often, picking up a heavy object is actually easier than trying to slide it across the floor Pushing FRICTION

19. Types of friction 1. Sliding- produced when solid objects slide over each other 2. Rolling Friction- produced by wheels 3. Fluid friction- created when an object moves through/across a fluid (water, oil or air)

20. Check out this Friction Board!!

21. Examples of Friction • Come up with atleast two examples of each friction: sliding, rolling and fluid • Come up with atleast two examples during which friction would be helpful

22. Label with the type of friction: Rolling Friction

23. Label with the type of friction: Fluid Friction

24. Label with the type of friction: • The movement of lubricated engine parts

25. Label with the type of friction: Rolling Friction

26. Label with the type of friction: Rolling Friction

27. Label with the type of friction: Sliding Friction

28. Label with the type of friction: Fluid Friction

29. When Friction is Helpful

30. Compare these two animations. How can the differences be explained? With air resistance Without air resistance

31. No Gravity: What will happen when the banana is shot from the cannon?

32. With Gravity: What will happen when the banana is shot from the cannon?

33. You will view a photograph of two balls being released from an apparatus. Which will hit the ground first? The one dropped straight down or the one shot out sideways?Website: http://www.fearofphysics.com/XYIndep/xyindep.html

34. Projectile Motion Tutorial Online: http://www.mhhe.com/physsci/physical/giambattista/proj/projectile.html

35. Work A force acting through a distance to move an object Must be moved over a distance Object must move in direction of force Work = force x distance

36. Work Examples Pushing a desk Throwing a baseball Lifting a shovel Not Examples Carrying a grocery bag Pushing on a wall Carrying a shovelful of snow

37. Work or Not??? Explain • Picking up a grocery bag • Carrying a grocery bag to the door • Throwing a baseball 20 meters • Lifting a suitcase to put into the overhead luggage compartment • Pushing against a cement slab until exhausted

38. Work or Not??? Explain • Carrying a bag of cat litter home from the store • Slamming a tennis ball across the net • Studying all night for the science test • Finger pushing down the RETURN key on a computer

39. Work or Not??? Explain • Carrying a shovel full of snow from the driveway to the lawn • You and a friend pushing a heavy piano across a wooden floor • Standing for half and hour in the freezing cold waiting for the bus to come

40. Work Example • If you lifted an object weighing 200 N through a distance of 0.5 m, how much work would you do? • W = F x D = 200N x 0.5m = 100nm

41. Work Example • If you picked up a rock weighing 350 N for a distance of 1.0m, how much work would you do? • W = F x D = 350N x 1.0m = 210 nm

43. What do machines do? Change small forces into large forces Allow small forces to move large objects Change the size and direction of the force Doesn’t reduce work- divides it into smaller jobs

44. Inclined plane Ramp, slanted surface Ex: truck ramp

45. Wedge Moving inclined plane with edges Ex: knife, scissors, key

46. Screw Bar wrapped with threads for fastening Ex: Lightbulb Jar Lid

47. Lever Bar that pivots up and down Ex: hammer, teeter toter

48. Pulley Rope wrapped around a wheel Ex: window shade pull

49. Wheel and axle 2 different sized spinning circles Ex: fan, sawblade, screwdriver

50. Machine Assessment • Work with your group members to create your own examples (atleast two) for each machine: • Pulley • Lever • Wedge • Screw • Inclined plane • Wheel and axle