Describing and Measuring Motion When is an object

Describing and Measuring Motion • • When is an object in motion? What is a reference point? Calculate speed and velocity using SI units. Use graphs to show motion.

Motion change in position relative to a reference point

These bikers are NOT in motion relative to EACH OTHER! They are in motion relative to the roadside.

SPEED 100 miles hour distance time The International System of Units (SI) is the standard system of metric measurements used by scientists all over the world. the meter The basic SI unit for length (or distance) is _________.

Speed see page 24 • Constant – stays the same over the whole time practice

Average Speed • - speed may vary over the time • Avg S = total distance total time practice

Velocity • Speed in a given direction 100 mph Southwest Stop here and do practice

What is acceleration? • Speed • Changing direction ANY CHANGE IN VELOCITY

Calculation 4 m/s A = Vf -Vi t

Calculation 4 m/s A = 22 m/s – 4 m/s 3 s 22 m/s A = 18 m/s 3 s 6 m/s/s 3 sec later = OR 6 m/s 2 The bike is increasing speed by 6 m/s every sec.

Sample problem #1 • An eagle accelerates from 15 m/s to 22 m/s in 4 seconds. What is the eagle’s average acceleration?

Sample #2 • A car advertisement states that a certain car can accelerate from rest to 90 km/hr in 9 seconds. What is the car’s average acceleration?