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PHYS_2014_Lecture_2

# PHYS_2014_Lecture_2 - Lecture 2 Introduction to the Study...

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Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 1 There is a time and a place for everything. Much of Physics is concerned with determining the time and place ( position or location), and the relation between time and place, of the myriad stuff that make up the Physical World. Motion Forces Mechanics Lecture 2: Introduction to the Study of Motion

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Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 2 Fundamental Quantities All other quantities in Mechanics can be expressed (i.e. described mathematically) in terms of these three fundamental quantities. time (seconds, minutes, hours, years,…) length (inches, feet, miles,… or …, millimeters, centimeters, meters, kilometers,…) mass (pounds, slugs…, or …, milligrams, grams, kilograms,…)
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 3 Systéme International (SI) Units time: second, s length: meter, m (3.281 ft) mass: kilogram, kg (2.205 lbs. where acceleration due to gravity is 32.174 ft/s 2 ) Sometimes referred to as the MKS ( meter-kilogram-second ) system (as opposed to the older cgs or centimeter-gram- second system or the English system of feet-pounds- seconds). In this course, we mainly use SI units.

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Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 4 Converting Units We are often given problems that are in units other than SI units. We must convert the those units into their SI equivalents. e.g. what is 70 mph in SI units (m/s)? miles 70 km 1.609 hr mile × km 112.63 hr km 112.63 = m 1000 hr km × m 112,648 hr m 112,648 hr = 1 s 3600 hr × m 31 s =
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 5 Straight Line (one dimensional) Motion When I roll a billiard ball, how does its position change in (as a function of) time? This is a question of kinematics. Kinematics is the mathematical description of motion. It is the “what’s happening” of motion, not the how or why.

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Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 6 Speed The simplest way to relate the change in position of an object, Δ x , to the corresponding change in time, Δ t , is to take the ratio of the two. We call this speed . We use the Greek letter Δ to mean “the change in.” Δ the change in position speed, Δ the change in time = = x v t position, x (m) Δ x time, t (s) 0 1 2 3 4 5 0 1 2 3 4 5 Δ t
Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 7 I live about 25 km (~15 miles) from the OSU campus. If I leave my house at 7:00 am and I arrive at the campus at 7:30 am, at what speed do I travel from my home to campus? m 25 km 1000 25000 m km m 14 s s 1800 s 30 min 60 min × Δ = = = = Δ × x v t m 14 s ft 3.281 × m 1 ft 5280 × s 3600 mile × miles 31 hr hr = Let us express this in a way that is more familiar:

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Fall 2010 Oklahoma State University PHYS2014: Benton Lecture 2, Slide 8 Δ the change in position average speed, Δ the change in time = = x v t At 31 miles/hr, at first glance it would appear that I drive like a grandmother. But that is because there is more to the story; many details of my drive to campus were left out: • the time I spent at stop lights going nowhere,
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PHYS_2014_Lecture_2 - Lecture 2 Introduction to the Study...

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