Intro to Physics Part 2: Scalars and Vectors Communicating the Position of an Object

Framing Questions What is the difference between a scalar quantity and a vector quantity? How can I identify these? How do I precisely communicate the position of an object? What are the four things I need to include when indicating position?

Scalars and Vectors ScalarsVectors Definition Give only a magnitude (quantity) Give a magnitude and a direction How Indicate? Italicize Use arrow (→) Examples d = 40 m d = 40 m due south = 40 m [S]

Practice Problems Identify each of the following as being a vector or a scalar quantity: s L 3.14 m [NW] 4.19 s to the right calories cm N66°E 7.33 min from the final destination m deep 9.74 km straight down in the mine shaft km/h

Communicating the Position of an Object When we talk about the position of an object in physics, we need to be as precise as possible. Why? (Demo) Physics is all about …

A Word About Being Precise… Precision means being as exact as possible. In physics, we need to be exact with our measurements and our descriptions of position and motion Precise measurements = exactly how much Precise measurements = exactly how much Use appropriate measuring tools Round to the nearest decimal Give the unit of measurement Precise descriptions = exactly where (direction, angle) Precise descriptions = exactly where (direction, angle) Tell which direction, at which angle, etc. Make sure it is unambiguous! (This means it should only be able to be interpreted in ONE way)

Communicating the Position of an Object, Continued… The four necessary parts of the communication are: 1. Origin (start or initial position) 2. Magnitude 3. Unit 4. Direction

Part 1: Origin When we’re talking about motion in physics, we describe “how far” or “how fast”… but from what? When we’re talking about motion in physics, we describe “how far” or “how fast”… but from what? We need a point of origin for everything we talk about. We need a point of origin for everything we talk about. For example, if I give you a distance of 3m, you have to know there was a starting point from which the 3m was measured. For example, if I give you a distance of 3m, you have to know there was a starting point from which the 3m was measured.

Part 2: Magnitude The actual number that tells us the “how much?” or “how fast?” The actual number that tells us the “how much?” or “how fast?” It has to be relative to the point of origin It has to be relative to the point of origin It is always accompanied by a unit of measurement, so we are being as precise as possible. It is always accompanied by a unit of measurement, so we are being as precise as possible.

Part 3: Unit You should always try to use a well-defined unit of measurement so your activity can be replicated (repeated by someone else) Ex: “Three steps to the right” is not a precise or well- defined unit of measurement because my step may be larger than yours! Use metric units of measurement when possible: kilometer (km) = 1000m hectometer (hm) = 100m decameter (dam) = 10m basic unit = 1 METER m decimeter (dm) = 1/10m centimeter (cm) = 1/100m millimeter (mm) = 1/1000m

Part 4: Direction Be as precise as possible is your description of direction Ex: If I say “backwards”, technically you could go backwards at any angle, as long as you’re not going forwards. Examples of precise direction: 10km due south 10km due south 45˚NW 45˚NW 6 cm directly towards the back wall in a straight line 6 cm directly towards the back wall in a straight line