Fun Side of Mechanics Day 7: Fun and Review

1. Fun Side of Mechanics Day 7: Fun and Review Jonathan Abbott

2. A taste of Quantum: It’s a Wave • In quantum, you learn that everything (light and mass) is a wave. This is pretty hard to believe because we don’t see it, but it is evident when you look at things that are very small (like little particles). • http://youtu.be/UANVMIajqlA

3. Speed Skating • Basic Inline Skating • http://youtu.be/OXWGB3aQTzI • Double Push • http://www.youtube.com/watch?v=4ZovJ1FPmBg • Think where the friction is and how it is used to propel the skaters. • Also notice what the arms do. What physics concept might the arms help with.

4. Figure Skating • http://youtu.be/_-xwx-Z3ijc • Look for countersteeringand conservation of angular momentum

5. Car Engine • We generally have an internal combustion engine. • This means that energy from gasoline is released (as it catches on fire) to kinetic energy using a motor. • http://auto.howstuffworks.com/engine1.htm • We will look at a piston and learn about some of the other parts of a car engine.

6. Jobs (Do they Use Mechanics) • Check out bls.gov for their occupation outlook handbook for tons of job information. • Chemist • Accountant • Actor • Actuary • Agricultural and food scientist • Architect • Artist • Automotive mechanic • Bookkeeping clerk • Carpenter • Childcare worker • Civil engineer • Coach • Computer hardware engineer • Computer software engineer • Computer support specialist • Cost estimator • Court reporter • Dancer • Database administrator • Designer • Desktop publisher • Disc jockey • Doctor • Drafter • Economist • Electrical engineer • Electrician • Engineering technician • Environmental scientist • Farmer • Financial analyst • Firefighter • Human resources assistant • Judge • Landscape architect • Lawyer • Librarian • Loan officer • Musician • Nurse • Paralegal • Pharmacist • Photographer • Physicist • Pilot • Police officer • Politician • Professional athlete • Psychologist • Real estate agent • Recreation and fitness worker • Recreational therapist • Reporter • Secretary • Social worker • Statistician • Surveyor • Systems analyst • Teacher • Urban planner • Veterinarian • Webmaster • Writer • Zookeeper

7. Economics model like PhysicsPhysics model of Damped Harmonic Motion Applies to US Recession Ideal growth Actual Economy GDP Second Dip Recession Time

8. REVIEW: What was Mechanics? • Mechanics: • Geometry in motion or study of motion

9. REVIEW: What was Force, What was newton’s Second Law • Force: A push or a pull • Newton’s Second law: • F=ma. • Force = mass * acceleration

10. REVIEW: What was Net Force, What was newton’s First Law Just keep pedaling, just keep pedaling

11. REVIEW: What was Net Force, What was newton’s First Law Just keep pedaling, just keep pedaling

12. REVIEW: Free Body Diagrams

13. REVIEW: Friction – Kinetic Vs. Static

14. REVIEW: Newton’s Third Law & Action Reaction Pairs 1 2 3

15. REVIEW: Counter Steering Normal Turn right to lean Turn left

16. REVIEW: Momentum/Collisions

17. REVIEW: Energy, Mechanical Energy

18. REVIEW: Translation Vs. Rotation

19. REVIEW: Torque, Moment of Inertia, Angular Momentum

20. Review: Two methods of Balance Countersteering Continuum Twist body Change Point of Contact Change Shape of Body Translation Rotation Use both techniques to balance best

21. Review Impulse I should have worn a helmet… Impulse = Change in Momentum = Force * Time

22. Centripetal Force Review • We call this force that causes circular motion the centripetal force. • ‘Centripetal’ means center seeking • Why might the rollercoaster passengers not fall out during the loop shown below? [Hint: draw a free body diagram]

23. Centripetal Forces Example • Conceptual Question: Why are roads banked?

24. Right Hand Rule • Remember angular momentum (w)? • We used an arrow to describe rotation. • A bigger arrow = spin faster, more rotational inertia • We can use an arrow to describe torque (and it relates to angular momentum). • Torque = rx F • Torque = radial vector cross the force

25. Right hand rule • Torque = rx F • Torque = radial vector cross the force • Curl your fingers from the radial vector to the force (your palm). • Your thumb here should point ‘out of the page’

26. Right Hand Rule continued • The cool thing is that the torque vector points in the direction the angular momentum is increasing.

27. Precession/Gyroscopes A spinning object can precess or rotate when a torque is applied perpendicular to the axis of rotation This is due to conservation of angular momentum and can be shown with the right hand rule. http://youtu.be/8H98BgRzpOM http://www.flickr.com/photos/loopzilla/94042474/sizes/m/in/photostream/

28. Advanced turning and Gravitational Potential Energy • By leaning your unicycle, you automatically want to turn. • You can do this: Have you ever ridden a bike with no hands? How can you turn? You turn by leaning the bicycle underneath you. Gravity pulls on your body, putting pressure on the tires making you want to turn. • It’s hard to see without some pictures…

29. Leaning

30. Riding a bike with no hands • I don’t recommend it, but it is possible. • Let’s go back to the unicycle. I said that when the unicycle wheel was leaning to one side, the unique would naturally “turn.” This was due to gravitational potential energy. Let’s explore this further.

31. Gravitational Potential Well • The unicycle wants to be the closest to the ground that it can (too bad for me)… • So if the unicycle is tilted front or back, the center of mass of the unique actually is higher than if the unicycle is square to the ground. Notice how the unicycle wheel is actually shifted up in the right picture. Gravity pull the unicycle to it is closest to the ground like the left picture.

32. What does this mean? • This means that if you can ‘tilt’ the wheel, gravity will do the work to turn the wheel for you. YOU CAN DO THIS!!! • Bikes are designed so that the front wheel is actually “unstable” and the front wheel will naturally want to turn so the bike is closer to the ground

33. Unstable: tilt = Turn “Axis of Rotation” • As you tilt the bike (by twisting your body) you make the front wheel naturally try to turn in the direction you are leaning • Then you have to do some impressive countersteering in order to fully stay upright. • Note: why doesn’t the front wheel easily turn? • The faster you go, the greater a “restoring force” (friction) keeps wheel straight. • Hence, you have to be going fairly fast to ride with no hands. Gravity Normal force Friction

34. Front Tire: A closer Look Looking down from “axis of rotation” “Axis of Rotation” The net torque about the axis of rotation is small because friction is a great restoring force. Gravity The net torque is small; the restoring force of friction depends on your speed as you turn Normal force Normal force Friction Friction