Motion a change in position over a certain

Motion • a change in position, over a certain amount of time • is relative to a frame of reference – Example: • How fast are you traveling compared to your seat? – 0 miles per hour • How fast are you going relative to the sun? – 66, 500 miles per hour • So which is it? Are you moving 0 miles per hour or 66, 500 miles per hour? – Both are correct. Depends on how you define your frame of reference.

Frame of reference practice • A student is sitting on a school bus. the bus is traveling 50 miles per hour relative to road. – 1. How fast is the student traveling relative to the road? – 2. How fast is the student traveling relative to the bus?

More Practice • Same bus going 50 mi/hr relative to road. – Student gets up and walks 5 mi/hr forward relative to bus. • How fast is student traveling relative to road? • How fast relative to another bus traveling in opposite direction at 50 mi/hr relative to road? • How fast relative to another student walking on other bus walking 5 mi/hr relative to road towards back of bus?

More practice • Same bus same student walking to front of bus. – How fast is student moving relative to another bus going in the same direction at 55 mi/hr? • Just remember, motion of an object always must be compared to another object.

Speed • a measure of how fast something moves, • the distance it moves, in a given amount of time • Formula: Speed = distance time • in physics, we use the units of meters/second 00: 00. 0 5 4 3 12 6 What is the ball’s speed? 6 meters

Interesting Speeds meters/second miles/hour Cockroach 1. 25 2. 8 Kangaroo 15 34 Cheetah 27 60 Sound 343 767 Space Shuttle 7, 823 17, 500 Light 300, 000 671, 080, 888 (in 200 C air) (getting into orbit)

Practice Problems - Speed 1. If you walk for 1. 5 hours and travel 7. 5 km, what is your average speed? S=d t 2. S= 7. 5 km = 1. 5 hr 5 km hr Calculate the speed of a bee that flies 22 meters in 2 seconds. S=d t S= 22 m 2 sec = 11 m sec

Complete the speed problems on your own • See Handout.