Distance displacement speed acceleration State the obvious motion

Distance, displacement, speed, acceleration

State the obvious…. motion • When something has changed position, motion must have occurred • Some motion is obvious. Delivery truck at your house. Later the delivery truck is down the street. Obviously, motion has occurred. • So what is relative motion?

Example • Imagine you’re traveling in a train. It’s a long ride so you’re keeping yourself busy by quietly reading a book • Is the book moving? • Lets re-word that question • Is the book moving relative to you? • Is the book moving relative to someone watching the train go by? • What is relative motion?

Relative motion • It means “as it related to” • The book is moving relative to the person watching the train go by. The book is not moving relative to you

Distance vs. Displacement • Abigail leaves her house and travels 4 blocks north, 4 blocks west, 4 blocks south and then 4 blocks east. How far did she go? • There are 2 correct answers. Can you name them both? • Answer 1: 16 blocks. 4+4+4+4 = 16 • Answer 2: Nowhere. She ended right where she started. • One of these answers describes Abigail’s distance and the other describes Abigail’s displacement. • What is the difference?

Distance vs. Displacement Distance • Total length traveled – Abigail's distance was 16 blocks – Used to calculate speed – Always positive – A scalar quantity (magnitude only) Displacement • Difference between where the object started and where it ended • Abigail's displacement was 0 blocks • Used to calculate velocity • Can be positive or negative • Vector quantity (magnitude and direction)

Distance vs. Displacement • You try: • Johnny left his house early in the morning for a run. He ran 2 miles north, 6 miles west, 3 miles north, 10 miles south, 8 miles east and then 2 miles west. • What distance did Johnny run? • What was Johnny’s displacement? • He traveled a distance of 31 miles. (whew!) • He was displaced 5 miles south of his starting point.

Reflect: • Is it possible for the distance to be greater than the displacement? Explain. • Is it possible for the displacement to be greater than the distance traveled? Explain.