Transcript Slide 1
PH 352 Dynamics (Walker ch. 5 - 6) Winter 2006 - NCSSM 1 Accelerometer Vertical Accelerometer: 0 G’s 1G 2 G’s 3 G’s 4 G’s Vertical Accelerations are those accelerations that occur from a change in direction. Whenever you turn through a loop or a corner, you undergo an acceleration. Each line represents 1 G. A G, or gravitational force, is equal to the pull of gravity. Since gravity pulls on you at a rate of 9.8 m/s2, the mass at the third line represents 2 G’s, or an acceleration of 19.6 m/s2 . The first line represents 0 G’s. When you see 0 G’s, you are in a state of freefall! To properly use the vertical accelerometer, hold the tube in your hand, with the rubber band around your wrist. At all times hold the tube vertical, or perpendicular to the floor. (Make sure the bottom points down to the floor of the roller coaster at all times, allowing the mass to move up and down in the tube freely.) • 2. Horizontal Accelerometer – Is used to measure horizontal accelerations which result from an acceleration due to a change of speed. You will use it on rides like Tanganyika Tidal Wave, during a splash, or on the Ubanga Banga Bumper Cars, during a collision. The horizontal accelerometer should always be held with the edge toward you. It should not be held with the face, as currently shown, toward you. 2 Roller Coaster Loops http://physics.k12albemarle.org/teacher/circular/LoopDesign/home .html http://www.vast.org/vip/book/PDFFILES/PART1B.PDF (page 59, 62, 63) http://www.answerbag.com/c_view.php/1866#q_14456 3 Who invented roller coasters? Historians agree that the ride's origins were the Russian Ice Slides. These slides first appeared during the 17th century throughout Russia, with a particular concentration in the area of in what would become St. Petersburg. • The first "real" roller coaster, (one built with wheels on a dry track), was constructed on orders of Catherine the Great. The roller coaster was built in the Gardens of Oreinbaum in St. Petersburg in an amusement center called Katalnaya Gorka in the year 1784. Soon after the first coaster was built, the Napoleonic Wars began. Many French soldiers grew fond of the ice slides while in Russia and brought the idea of the roller coaster back with them to France. . . The first two roller coasters that operated on a continuous circuit were built in the early 1800s in France. One was named Les Montages Russes (The Russian Mountain) was built in Belleville. • Quickly the thrilling Gravity Road became a public attraction. Coal was hauled in the morning, but the afternoon runs were filled with passengers paying 50 cents per ride. By the mid-19th century, the demand for coal was increasing, so White added a backtrack with two 120horsepower steam engines at the top of nearby Mount Pisgah, which pulled the trains up the incline of 664 vertical feet, assisted by "barney," or "safety," cars. • The early history of roller coasters seems to have many disputes about exactly who invented the thrill ride. Hopefully, this gives you some idea though :) 4 Friction Forces • 1.When does friction occur? • 2. What does the frictional force depend on? • 3. How many types of friction forces are there? (related with the object being at rest or in motion) • 4. Is static friction constant? • 5. Is kinetic friction constant? • 6. When does the object start to move? 5 Static and Kinetic Friction 1. "Static" or "sliding" friction This type of friction occurs when dry surfaces rub together. The frictional force depends only on: -the type of surfaces - how hard the surfaces are pressed together. • • • • STATIC FRICTION FORCE The object is STATIONARY As you begin to push on a stationary object, it doesn't move. Static friction increases to oppose the force of your push, until you push hard enough and the object begins to move. • • • • KINETIC FRICTION FORCE The object is MOVING When the object starts to move the friction between the object and the surface lessens and is called kinetic friction. Kinetic friction is constant regardless of velocity. If we push the block harder and harder, the frictional force will increase, until it reaches a maximum (in this case, 2.5N). If we push harder still, (say, 2.6N), the block will start to move, because we're now 6 pushing harder than the frictional force. Static & Kinetic Friction • Static Friction Force • Kinetic Friction Force 7 Static & Kinetic Friction on Incline 8 Circular Motion Animation Back Seat Passenger • • • http://k12.albemarle.org/Instruction/Physics/teacher/home.html http://physics.k12albemarle.org/teacher/circular/CarAndCurve.htm http://www.joma.org/mathDL/4/?pa=content&sa=viewDocument&nodeId=45 2&pf=1 • Vertical Circular Motion: roller coaster, water bucket, cars traveling on hilly roads • http://webphysics.davidson.edu/physlet_resources/bu_semester1/c8_vertic al.html Without a centripetal force, an object in motion continues along a straightline path. With a centripetal force, an object in motion will be accelerated and change its direction. 9 Banked Roadway • http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Circular%20Motion/turning_a_car.htm 10 Circular Motion 11 Interesting Links • http://physics.bu.edu/~duffy/semester1/c05_elevator.html • http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Newton2/ElevatorProblem. html • • • • • • • • • • http://www.batesville.k12.in.us/physics/PhyNet/Mechanics/Newton2/ElevAnswers.htm l http://acept.la.asu.edu/courses/phs110/ds3/pl4.html http://hyperphysics.phy-astr.gsu.edu/hbase/elev.html#c1 http://wps.aw.com/aw_young_physics_11/0,8076,898588content,00.html#Circular%20Motion http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/circmot/rcd.html http://physics.k12albemarle.org/teacher/circular/CarAndCurve.htm 12