Describing and Measuring Motion

Vocabulary Motion-The state in which one object’s distance from another is changing. Reference Point-A place or object used for comparison to determine if an object is in motion. Speed-The distance an object travels in one unit of time. Velocity-Speed in a given direction. Acceleration-The rate at which velocity changes.

Reference Points An object is in motion if it changes position relative to a fixed reference point.

Reference Points If the reference points are moving, it is difficult to detect relative motion.

Describing Distance Basic SI unit of distance is the meter. 100 cm= 1 meter 1000 mm= 1 meter 1000 meters = 1 kilometer

Describing Distance 100 cm = _______ 1 meter 148 cm =_______ 1.48 meters 9 cm= ________ .09 meters 1248 cm = ________ 12.48 meters 450 cm =________ 4.5 meters

Calculating Speed Example. If a car travels 50 kilometers in 2 hours. What is the speed? 25 Km/hr.

Constant vs Average Speed Most objects do not travel at a constant speed. If an object speeds up or slow down, the speed is an average speed. The Earth’s rotation is not even constant. It is slowing down at a very slow rate.

Velocity Speed in a given direction is velocity. Directions can be given in cardinal directions or angular directions.

Acceleration Rate at which velocity changes. Increasing Speed. Decreasing Speed. Changing Direction.

Increasing Speed If an object begins from rest it is has accelerated.

Decreasing Speed Slowing down is referred to de-acceleration. If an object stops motion it is has changed speeds.

Changing Directions. An object that is going a constant speed but is changing directions is accelerating.

Calculating Acceleration Acceleration= (Final Velocity-Initial Velocity)/Time Example (22 m/s – 4 m/s)/3s 18 m/s / 3s 6 m/s/s = Acceleration