# Chapter 1, Section 1 Describing and Measuring Motion

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Chapter 1, Section 1 Describing and Measuring Motion

Describing Motion Not always easy to describe if an object is moving
“An object is in motion if its distance from another object is changing.” (p7)

Reference Point – a place or object used for comparison to determine if something is in motion. (p7)
Use objects like trees or buildings The answer to the question “is it moving?” depends upon the reference point chosen. Ex. A chair vs. the sun (p.8)

Use measurement to be more specific when describing motion.
International System of Units (SI) – system of measurement used by scientists. Unit of measurement used for length is meters (m) May also be in centimeters (cm), millimeters (mm), etc.

Calculating Speed You can calculate speed if you know both the distance and object traveled and how long it took to reach its destination. Speed = Distance / Time If distance is measured in meters and time is measured in seconds, your answer would be labeled m/s (meters per second).

Most objects to not move at a continuous speed
Most objects to not move at a continuous speed. It changes as the object moves (may speed up or slow down) Average Speed – total distance traveled divided by the total time. Instantaneous Speed – the rate at which an object is moving at a specific time.

Describing Velocity To fully describe the motion of an object you also need to know the direction it is traveling. Velocity – speed in a given direction Ex. 25 mph west Important for air traffic controllers to know the speed and direction of planes Important for pilots and stunt pilots to be able to keep control of the airplane

Graphing Motion To show motion in a graph, create a line graph.
Time is on the x-axis Distance is on the y-axis