Introduction to Forces

1. Introduction to Forces

2. Forces (F) • Definition: a push or pull that has the ability to cause a change in motion • Standard unit is the Newton

3. Where did this unit come from?? Sir Isaac Newton • English physicist and mathematician • Laws of Motion and Gravitation • Invented Calculus All before the age of 30!

4. Types of Forces • Forces cause motion • Motion depends on net force • NET means “total” or “sum” Forces can bebalancedorunbalanced

5. Like a tie in an arm wrestling match! • Equal in size Balanced Forces • Opposite in direction • No motion occurs! (equilibrium) p. 51

6. Unbalanced Forces • Unequal in size • Can be in the same direction OR in opposite directions • Forces must be unbalanced to cause a change in motion

8. As a box is sliding down a ramp, a 10 N force of gravity is pulling the box down the ramp while a 2 N force of friction acts to stop the box. What is the net (total) force accelerating the box down the ramp? (Magnitude and Direction!!) 8 N to the Right

9. What is the Net Force??? Fnet = 1N – 3 N = -2N 1 N 3 N Fnet = 1N +1 N = +2N 1 N 1N Fnet = -1N – 1 N = -2N 1 N 1N

10. a force that goes against motion Friction Four Types of Friction: 1. Air friction (Resistance) 2. Viscous friction 3. Sliding friction 4. Rolling friction

11. 1. Air Friction Also calledAir resistance (aerodynamics reduce the air friction) Ex - falling objects or airplanes

12. 2. Viscous Friction Moving through a liquid, or fluid • Ex. - swimming

13. 3. Sliding Friction Ex - rubbing hands or clapping Two surfaces rub against one another Oil and other lubricants help reduce friction.

14. Ex – any object with wheels 4. Rolling Friction An object rolls over a surface A_World_Without_Friction.asf

15. Mass, Weight and Gravity

16. Gravity • Def. - A downward force that causes objects to accelerate to the center of mass Gravity causes all falling objects to accelerate at the same rate.(9.8 m/s2)

17. Free Fall Tower Gizmo

18. Video Clips • Apollo 15 Hammer and Feather Drop • Mythbusters Recreates Apollo 15 Drop

19. (g) Mass Amount of matter inside of an object Is NOT (N) Weight A measure of the force created as your mass responds to gravity

20. Calculating Weight g m = Fw Formula: Force of Weight (N) Mass (Kg) Gravity = 9.8 m/s2 p. 53

21. Let’s look at how mass, weight, and gravity are related. • MassDOES NOTchange, but your weightwill change if there is a change in gravity

22. What would happen to your weight if you were on the Moon? • What would happen to your mass if you were on the Moon?

23. Weight and Mass Gizmo

24. Law of Universal Gravitation Newton said that gravitational force depends on 2 things: The DISTANCE from the center of gravity The MASS of the objects LESS gravitational force The yellowobject has more gravitational force than the red object because the yellow object has more MASS. MORE gravitational force

25. The mass of the moon is much smaller than the mass of the Earth, so the Moon is controlled by the gravitational pull of the Earth. The pull of gravity also keeps satellites orbiting around the Earth

26. Does the moon’s gravitational pull effect the Earth? Yes, the moon’s gravity is large enough to actually pull water out of the ocean from space… Well, not quite that much...just enough to create motion of the tides.

27. As you move further from the center of the Earth, the force of gravity DECREASES. • Where would you weigh less, in Galveston or in Denver? • Denver is the “Mile High City”; the force of gravity is less. Therefore, the force of gravity would be less because it is further away from the center of the Earth, and you would weigh slightly less. Gravity Song!

28. Newton's 1st Law Of Motion

29. Newton’s First Law (Law of Inertia) • An object at rest stays at rest and an object in motion keeps its same motion, UNLESS an outside force acts on it. Teenage Terms – Objects will keep doing what they are doing unless an outside force changes that!

30. Inertia • Def. - The tendency of an object to resist any change in motion • You must overcome inertia to start or stop motion • Depends on the mass of the object Asmass , inertia will

31. Which object has the greatest amount of INERTIA?? • Pencil • Baseball • Bowling Ball • Ping Pong Ball

32. INERTIA is what causes a person (or anything else in the) involved in a head-on collision to continue moving forward at the same speed that the car was traveling, until some outside force causes it to stop (i.e.- seatbelt, windshield, etc.)

33. Injuries Sustained in a Car Crash VIDEO CLIP

34. What’s wrong with this picture??

35. Inertia

36. Other Examples of 1st Law • Card Tricks • Dishes and table cloth • Collisions and seatbelts • Crash Test Dummies • Bike Ramp Crash • First Law, Inertia, and Friction Video

37. Newton's 2nd Law Of Motion

38. Newton’s 2nd Law (F = ma) • The acceleration of an object is directlyproportional to the force acting on it and inverselyproportional to its mass. F, a (direct relationship) m, a (inverse relationship)

39. Force and Acceleration areDirectly Proportional F a 2 N F=ma 2N =(1kg)a a= 2 m/s2 4 N F=ma 4N =(1kg)a a= 4 m/s2

40. Mass and Acceleration areInversely Proportional m, a (inverse relationship) F = ma 1 N = (1kg) a a = 1m/s2 F= ma 1 N = (2kg) a a = 0.5 m/s2

41. Unit for Mass is kilograms (kg) Unit for Acceleration is m/s2 Unit for Force is Newtons (N) Solving 2nd Law Problems Use the formula: F = ma

42. Solving 2nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s2 ? Variables Formula Plug-n chug Answer F= ? m=5 kg a= 2m/s2

43. Solving 2nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s2 ? Variables Formula Plug-n chug Answer F= ? F = ma m=5 kg a= 2m/s2

44. Solving 2nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s2 ? Variables Formula Plug-n chug Answer F= ? F = ma F =(5kg)(2m/s2) m=5 kg a= 2m/s2

45. Solving 2nd Law Problems What force is required to give a 5 kg box an acceleration of 2 m/s2 ? Variables Formula Plug-n chug Answer F= ? F = ma F =(5kg)(2m/s2) m=5 kg a= 2m/s2F= 10N

46. Solving 2nd Law Problems • Explains why you can throw a baseball further than a bowling ball • Braking force required to stop a Volkswagen vs. a dump truck • Why a Mustang accelerates faster than a bus

48. CLASS PRACTICE • What is the acceleration of a 500 kg ball rolled with a force of 3.6N? • A rollercoaster accelerates at a rate of 30 m/s2. If the rollercoaster has a mass of 10,345 kg, what size force must be applied? • What is the mass of a tanker truck that accelerates at 15 m/s2 with a force of 2500 N?

49. Newton's 3rd Law Of Motion

50. Newton’s 3rd Law (Action/Reaction) • Whenever one object exerts a force on another (action), the second object exerts an equal and opposite force (reaction) on the first. • All forces come in pairs.