Intro - 3 - Reference Frames, Coordinates, Labs

0.3-0.5: Reference Frames, Coordinate Systems, and Lab Reports Quantum Ch 6: Frames of Reference 1 2 Frames of Reference  To study motion you need to know an object’s precise position & time.  Eg GPS uses satellites in reference with: The centre of the earth  The Atomic clock   Example p153  Conclusion: Motion is relative to the frame of reference that is used 3 0.3 Frames of Reference A frame of reference (f.o.r.) eliminates confusion due to viewpoint.  Generally an origin 0 and three axes (x, y, z) are used.  Inertial f.o.r. = the object is at rest or in uniform rectilinear motion.   Two observers will agree on measurements if they are in an inertial viewpoint! 4 0.3 Frames of Reference   Other frames of reference include… Terrestrial f.o.r. = origin is fixed point on earth’s surface.   Geocentric f.o.r. = origin is centre of the earth.   Experiments on earth are not affected by its rotation. Eg GPS, the motion of satellites. Heliocentric f.o.r. = origin is centre of the sun.  Eg. Planetary studies 5 0.4 Coordinate Systems Coordinate systems give a position on the x, y and z axes for accurate location.  We will consider motion in 2 directions only.    Just the x-axis & the y-axis!!!!! We will use:   Cartesian coordinate system Polar coordinate system 6 Cartesian coordinate system.  Each point can be located with:    X-coordinate (independent) Y-coordinate (dependent) Point 0 is the origin (0,0) 7 Polar Coordinate System Point 0 is called the pole.  Positive X-axis is called the polar axis.  (radial coordinate, angular coordinate)  (distance from 0 to P, angle θ)  Trigonometric direction.  8 Transformation: Polar to Cartesian  We can transform from (r,θ) to (x,y) via the following formulae:   x=r*cos(θ) y=r*sin(θ) 9  Cartesian coordinate system:  Each point is in reference to the origin 0.  A point is described using an (x, y)  Polar coordinate system:  Each point is in reference to the pole.  A point is described by (r, θ)  Transform via:  x=r*cos(θ) and y=r*sin(θ) 10 Can You Cancel Velocity? (https://www.youtube.com/watch?v=qQVDAMzo4mE) Relativity Paradox (https://www.youtube.com/watch?v=wteiuxyqtoM) How Fast Are You Moving? (https://www.youtube.com/watch?v=wD7C4V9smG4) 11 0.5 Lab Reports Two types: formal and informal  Formal Lab: contains the following (typed) sections:         Purpose: what are you doing and why? Materials: what did you use? Procedure: how did you do it (step by step)? Diagrams (optional): what did it look like? Observations: what did you measure or record? Calculations: what did you calculate from your obs? Conclusion/Discussion: did you accomplish your purpose, plus any other questions. 12 0.5 Lab Reports (cont.)  Informal Lab:    Do not have to write out purpose/materials/procedure Usually contains only observations, calculations and discussion questions. For all labs, a marking rubric is provided outlining exactly which sections are required for that lab. Read it! 13 0.5 Lab Reports (cont.)  Sources of error:    Does not include those things for which you know a numerical measurement uncertainty (ie the ruler) “Human error” (must be specific!) Think… what could have affected my results in my lab with my setup?  Ex: In a motion lab, friction between two parts or surfaces that you can’t measure may affect your results. It could be valid to mention that.