Physics … Force & Motion

1. Physics… Force & Motion

3. FORCE… • “Any influence that can cause a body to be accelerated. It is measured in NEWTONS.” • A Newton is the force needed to accelerate one kg one meter per second per second • A push or pull exerted by an object to/on another object

4. FORCE cont… • Always occurs in pairs (Sometimes called Agent & Receiver) • It can alter the shape or motion of an object • It is represented by arrows that show direction and size

5. Demos • Rolling Ball Shows Acceleration • Push – Pull; Pushing a closed door; standing on the floor All show that forces occur in pairs

6. Clay ball Shows how force is required to change shape • Tennis ball Change of shape- Elasticity • Pushing on a table Forces occur in pairs; Net Force

7. Tennis Ball • http://www.youtube.com/watch?v=sxS-m9CRu34 • Rubber Ball • http://www.youtube.com/watch?v=N8gxND1kX6k

8. Paired Verbal Fluency • Read the biography of Sir Isaac Newton • Find a Partner • Decide who will go first

9. Isaac Newtonb: 25 Dec 1642 d: 31 March 1727 Principia MathematicaPhilosophiae Naturalis

10. Newton’s Three Laws of Motion

11. Law #1: • “Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it.” • Sometimes called the Law of Inertia

12. What isInertia? • “The sluggishness or apparent resistance a body offers to changes in its state of motion” • The larger the mass, the larger its inertia • A body with less mass is easier to accelerate • A body with more mass is harder to accelerate

13. Demo • Tennis Ball and Cup Tennis ball has inertia; Newton’s First Law

15. http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/http://www.teachersdomain.org/resource/phy03.sci.phys.mfw.galileoplane/ • http://www.youtube.com/watch?v=WOvwwO-l4ps

16. Demos: • Ping pong ball Small inertia; easy to move & stop • Bowling ball Larger inertia; hard to move & stop • Granny Small inertia; easy to move & stop • Mack Truck driven by Granny  Larger inertia; hard to move & stop

17. Mass • Defined as “The quantity of matter in a body” • It is the measure of Inertia m = mass; F = force; a = acceleration m = F/a F = m(a) a = F/m

18. Momentum • The product of MASS and VELOCITY • It is inertia in motion • Are you afraid of a piece of grass?

19. Straw (grass) Through Wood Small mass, great acceleration

20. Demos: • One Ounce Projectile A small mass accelerated at high velocity can be produce a lot of force • Newton’s Jar Momentum • Car on a ramp Momentum • Eeyore on a car on a ramp Momentum; inertia in motion

21. Conservation of Momentum • All energy stored in a moving object is not lost, but only changes form • This is just like “Energy cannot be created nor can it be destroyed, it can only change form” (Stated by: Albert Einstein; Phillip Morrison, Mr. Watts…)

22. Demos: • Newton’s Cradle Conservation of Momentum http://www.youtube.com/watch?v=7_AiV12XBbI&safety_mode=true&persist_safety_mode=1&safe=active • Swinging Rock Potential and Kinetic energies; Conservation of Momentum

23. Mass in a Circular Motion • When object moves in circular path it has a property called Rotational Inertia • AKA: Gyroscopic Inertia

24. Circular Motion con’t… • “An object rotating about an axis tends to remain rotating about that same axis unless it is interfered with by some external force.” • This definition is similar to Newton’s First Law of Motion

25. Rotational Inertia Demos: • Bicycle tire • Gyroscope • Top • Frisbee • Football • Moment of Inertia • X-Zylo

27. Angular Momentum • A measure of an object’s rotation about a particular axis • For an object small compared to the radial distance, it is the product of mass, velocity and radius • It is the measure of the rotational property of motion • It is always perpendicular to the centripetal force

28. Angular Momentum

30. Demos: • Rolling objects • Washer on a string • Slingshot (old-fashioned!) • Bucket with water spun in vertical circles • Q: What holds the water in the bucket? • Spin cycle of washing machine • “Whizzer” • Brendan on the Scrambler

31. Carnival Ride Know-How • It’s better to take the OUTSIDE seat of the car if you’re riding alone • If you’re riding with someone else, take the INSIDE seat

32. The following formula is similar to those for Newton’s First Law, but deals with mass in motion in a circular path: mvr = mvr … The mass is not affected by a smaller radius, while velocity is…

33. What happens in this situation? m v r = ? v r

34. Demo • Spinning on a chair with weights • Arms Out? • Pulling arms in?

35. Centripetal Force • A center-seeking force that causes an object to follow a circular path.  • “Any force that is directed at right angles to the path of the moving body and produces circular motion.”

36. Centrifugal Force • A fictitious outward force due to rotation • It is a reaction to centripetal force but there is no agent, therefore it is experienced relative to position • What we are really experiencing is ANGULAR MOMENTUM!

37. Newton’s Second Law Law #2 • The acceleration of a body is directly proportional to the net force acting on the body and inversely proportional to the mass of the body and is in the direction of the NET FORCE

38. 2nd Law Formulas • You’ve seen these before: • a = F/m • F = m (a) • m = F/a

39. What is the acceleration of these?Acceleration is Inversely Proportional to mass… 5 N Acceleration = 6 kph Acceleration = ? 5 N 5 N Acceleration = ?

40. SolutionsAcceleration is Inversely Proportional to mass… 5 N Acceleration = 6 kph Mass is doubled so a/ 2 = 3 kph 5 N Mass is tripled so a/3 = 2 kph 5 N

41. Acceleration is Directly Proportional to force… 5 N Acceleration = 6 kph 10 N = (2 x f) Acceleration = 12 kph 15 N = (3 x f) Acceleration = 18 kph

42. What if I want the Acceleration to be the same for all these bodies?Acceleration is Directly Proportional to force… 5 N Acceleration = 6 kph 10 N = (2 x f) Acceleration = 6 kph 15 N = (3 x f) Acceleration = 6 kph

43. Newton’s Third Law 3rd Law • “Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first” • For every action, there is an equal and opposite reaction • You cannot touch without being touched

44. Demo • Syringe with water • Rocket Balloon • Beaker of Water on Balance

45. Common Forces • Gravitational – non contact Every object exerts an attractive force on every other object • Buoyancy - contact The tendency to float in a fluid • Friction - contact The resistance to motion where two objects touch

46. Common Forces • Magnetic – non contact The repelling or attraction of a magnet and ferromagnetic material • Elastic - contact Ability to spring back to its original size, shape, or position after being stretched, squeezed, flexed, expanded, etc. • Electrical – non contact Flow or gathering of a negative charge by electrons

47. Other Physics concepts of interest: • ENERGY The quality of an object that enables it to do work • Power WORK/ TIME

48. Potential Energy • The stored energy that a body possesses because of its position with respect to other bodies

49. Kinetic Energy • The energy of motion • Kinetic Energy = 1/2 mv2

50. As an object falls, its energy transformsfrom all Potential to all Kinetic P K K P