FUN SIDE OF MECHANICS DAY 7 FUN AND

FUN SIDE OF MECHANICS DAY 7: FUN AND REVIEW Jonathan Abbott

A TASTE OFQUANTUM: 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/UANVMIajql. A

SPEED SKATING Basic Inline Skating � http: //youtu. be/OXWGB 3 a. QTz. I Double Push � http: //www. youtube. com/watch? v=4 Zov. J 1 FPm. Bg 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.

FIGURE SKATING http: //youtu. be/_-xwx-Z 3 ijc Look for countersteering and conservation of angular momentum

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/engine 1. htm We will look at a piston and learn about some of the other parts of a car engine.

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 Environmenta l 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

ECONOMICS MODEL LIKE PHYSICS MODEL OF DAMPED HARMONIC MOTION APPLIES TO US RECESSION Ideal growth GDP Actual Economy Second Dip Recession Time

REVIEW: WHAT WAS MECHANICS? Mechanics: Geometry in motion or study of motion Physics Mechanics

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 Mechanics Force Newton’s Second Law

REVIEW: WHAT WAS NET FORCE, WHAT WAS NEWTON’S FIRST LAW Mechanics Force Newton’s Second Law Just keep pedaling, just keep pedaling Net Force Newton’s First Law

REVIEW: WHAT WAS NET FORCE, WHAT WAS NEWTON’S FIRST LAW Mechanics Force Newton’s Second Law Just keep pedaling, just keep pedaling Net Force Newton’s First Law

REVIEW: FREE BODY DIAGRAMS Mechanics Force Newton’s 1 st and 2 nd Law Free Body Diagram

REVIEW: FRICTION – KINETIC VS. STATIC Mechanics Force Newton’s 1 st and 2 nd Law Free Body Diagram Friction

REVIEW: NEWTON’S THIRD LAW & ACTION REACTION PAIRS Force Newton’s 1 st and 2 nd Law Free Body Diagram 1 2 3 Friction Newton’s Third Law Action Reaction Pair

REVIEW: COUNTER STEERING Mechanics Application: Balance Force Newton’s 3 Laws Normal Free Body Diagram Friction Turn right to lean Countersteering Turn left

REVIEW: MOMENTUM/COLLISIONS Mechanics Application: Balance Momentum Force Newton’s 3 Laws Friction

REVIEW: ENERGY, MECHANICAL ENERGY Mechanics Application: Balance Momentum Energy Force Newton’s 3 Laws Friction Kinetic Potential translation height rotation elastic Other

REVIEW: TRANSLATION VS. ROTATION Mechanics Translation Force Momentum Newton’s 3 Laws Free Body Diagram Friction Rotation Energy

REVIEW: TORQUE, MOMENT OF INERTIA, ANGULAR MOMENTUM Translation Rotation Force Torque Mass Moment of Inertia Momentum Angular Momentum

REVIEW: TWO METHODS OF BALANCE Countersteering Twist body Continuum Change Point of Contact Change Shape of Body Translation Rotation Use both techniques to balance best

REVIEW IMPULSE Mechanics Translation Force Rotation Energy Momentum Newton’s 3 Laws Free Body Diagram Friction Impulse = Change in Momentum = Force * Time I should have worn a helmet…

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]

CENTRIPETAL FORCES EXAMPLE Conceptual Question: Why are roads banked?

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 = r x F Torque = radial vector cross the force

RIGHT HAND RULE Torque = r x 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’

RIGHT HAND RULE CONTINUED The cool thing is that the torque vector points in the direction the angular momentum is increasing.

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/8 H 98 Bg Rzp. OM http: //www. flickr. com/photos/loopzilla/94042474/sizes/m/in/photostream/

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… 28

LEANING 29

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.

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.

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

UNSTABLE: TILT =TURN 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? “Axis of Rotation” 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 � The Friction

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