Forces + Friction Science Inquiry Grab the ½ sheet off the front table Force & Friction Notes

1. 1 Forces + Friction • Science Inquiry • Grab the ½ sheet off the front table • Force & Friction Notes • Friction Wheel • Force Flip Chart

2. 2 What causes things to move? • A force! • A push or a pull applied to an object.

3. 2 What is a Net Force? • Net Force • When two or more forces act on an object at the same time • 3 Types of Net Forces

4. 3 • Balanced No change in motion

5. 4 an Question: Can there be balanced forces on a object and the object still have motion?

6. 5 Unbalanced Forces • Unequal forces acting on an object meaning "unbalanced". • The object will: • Speed Up • Slow Down • Change Direction • In other words…. • The Body will “Accelerate”

7. 6

8. 5 • Combined Forces • Forces applied to an object in thesame direction • Add the forces together

9. 18 Friction - Forces that oppose motion

10. 20 Friction • What Causes Friction? • Tiny microscopic tears in between 2 surfaces

11. Types of Friction!!

12. Spiral Activity: Left Hand Side • Write examples of the 3 different types of forces • Draw pictures for each • You’ll be graded on • Effort • Color • examples

13. Forces that oppose motion 19 -Friction is a force that opposes motion between two surfaces that are touching each other. Friction Song 1 Friction Song 2 Acts in the opposite direction of the motion

14. Forces that oppose motion -Air resistance is the force air exerts on a moving object

15. 3 types of Friction • Static Friction • Sliding Friction • Rolling Friction

16. 21 Types of Friction • Types of friction: 1. Static – force required to overcome inertia of a stationary object

17. Static friction- occurs between the surfaces of 2 objects that touch but do not move against each other. Static friction must be overcome for one of the objects to move.

18. 22 Static Friction (FS)

19. Not enough static friction

20. 23 Types of Friction (cont’.) 2. Sliding – force required to keep an object sliding at a constant speed 3. Rolling – force required to keep an object rolling at a constant speed • To decrease friction, surfaces can be lubricated with a liquid such as oil.

21. Newton’s Laws!! Warm Up! - Identify the type of friction in each picture and EXPLAIN why you are correct.

22. What will happen? • Abruptly stopping a cart with a suitcase on top…. • You set your coffee cup on the dash and then make a sharp left turn….. • You throw a tennis ball in outer space.

23. Questions: How do we measure force? 7 Newtons • SI unit of force is the Newton (N). • Newton - the amount of force acting on a 1 kg of an object which produces an acceleration of 1m/s2. • Therefore, 1N = 1 kg m s2

24. 8 Newton’s First Law

25. 9 Newton’s First Law

26. 10 Newton’s First Law • An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force. • What do you mean by “Net Force”? • Net means:sum of all the forces acting on the object.

27. 11 Newton’s First Law • Newton’s First Law is also called the Law of Inertia. • Inertia is the tendency of an object to resist any change in its motion.

28. 12 Why does the ladder continue to move? Inertia!

29. 13 Why does the person continue to move? Inertia! Clip

30. Video Time!! https://www.youtube.com/watch?v=_mCC-68LyZM Question:Why does the medicine ball and basketball hit the ground at the same time? Be able to explain your answer…

31. 14 Newton’s Second Law • F=ma • Force = (mass)(acceleration) Kg m/s2

32. 15 F=50 kg m s2 M= 10 kg F=50 kg m s2 M= 20 kg

33. 16 Newton's 2nd Law of Motion: • F = m x a • Mass is in kg • Acceleration is in m/s2 • Force is in kg x m/ s2 (or N) Force = mass x acceleration Let’s do a sample problem…next slide 

34. 17 Force Problems: What force is needed to give an object with a mass of 25.0 kg an acceleration of 15.0 m/s2 ? Formula F = ma Unknown: Given: m = 25.0 kg a = 15.0 m/sec² F = ? F = (25 kg)(15 m/sec²) F = 375 kg•m/sec² = 375 N

35. 34 Newton’s Third Law of Motion …to every action force there is an equal and opposite reaction force

36. Action-Reaction forces act on different objects 35

37. 36

38. Hockey Video Clip

39. Newton’s Laws Comic Strip

40. 24 CLIP The amount of force required to overcome static friction is always greater than the force required to overcome sliding or rolling friction.

41. GRAVITY!! 25 • The force of gravity is an attractive force between objects. • The amount of GRAVITATIONAL FORCE between objects depends upon their: • 1- Masses (greater mass means more gravity) • 2- Distance apart (greater distance means less gravity) *All objects fall toward the earth at the same rate of acceleration, regardless of their masses!

42. 26 Calculating the Gravitational Force

43. Gravitation 27

44. 28 Weightlessness Gravity in Space Moon Moon Hammer & Feather

45. 29 Free fall and Terminal Velocity • The opposing force of air resistance increases with speed. • Objects accelerate towards the Earth until the force of gravity is cancelled or balanced by this air resistance. • This is the highest speed an object can reach. • Different objects have different terminal velocities.

46. Practice Problems

47. 30 Weight and Gravity • Weight is the force of gravity between the earth and a body on its surface. • Weight ≠ mass! • Weight is measured in Newtons (N). W =m x g BECAUSE IT’S A FORCE!

48. 31 Could your weight change by simply going to the top of a mountain?

49. 32 Weight • When the mass of an object and the acceleration due to gravity are known, the weight of an object can be calculated. W = (g)(m) Ex. Mass = 100kg Acc.= 9.81 m/s2 Weight = 981 N

50. 33 Example Problem • What is your weight if your mass 4.52 kilograms? Given: Unknown: m = 4.52 kg W = ? g = a = 9.8 m/sec² Formula: W = mg • W = (4.52kg)(9.8 m/sec²) • W = 44.296 kg•m/sec² = 44.296 N