Chap 1.1 – Describing and Measuring Motion

I. RECOGNIZING MOTION An object is in motion when its distance from another object is changing. Reference point: A place or object used from comparison to determine if something is moving.

** An object is in motion if it changes position relative to a reference point. For example, picture yourself sitting in a desk and me walking around the room. Who is in motion and why?

II. DESCRIBING DISTANCE Measurement system used by scientists is called the International System of Units (also called SI units). The International System of Units is based on multiplying or dividing by units of TENS.

For example, the SI unit of measuring length is a meter (not feet, yards, or inches). 1 meter = 100 centimeters (‘centi’ means 1/100) 1 meter = 1000 millimeters (‘milli’ means 1/1000) 1 kilometer = 1000 meters (“kilo” means 1000)

III. CALCULATING SPEED Speed = distance the object travels in one unit of time To calculate speed, divide distance by time. SPEED = DISTANCE (meter or km) TIME (such as sec., minutes, or hours) *Also use triangle formula.

Be aware of abbreviations: For distance: m = meter km = kilometer cm = centimeter mm = millimeter

For time: s = second m = minute h = hour For speed: km/h or m/s

III.A. CONSTANT SPEED Definition of constant speed: when an object travels at the same speed over a certain period of time. For example, your car is going exactly 45 miles/hour over the course of 30 minutes.

III.B. AVERAGE SPEED Definition of average speed: the rate are which an object keeps constant speed. To calculate average speed, divide total distance by total time. AVE. SPEED = TOTAL DISTANCE TOTAL TIME

IV. DESCRIBING VELOCITY Defintion of velocity: velocity is the SPEED and DIRECTION of an object. For example, velocity is expressed as 25 km/h eastward. Airplanes travel only according to velocity: 500 miles/hour southwest.

V. GRAPHING MOTION On a distance-time graph, look at the slope of the line in order to determine how fast or slow an object is moving. Slow positive constant speed (shallow slope, closer to X axis).

Fast positive constant speed (steep slope, closer to Y axis).

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