1. Ch.5, Sec.1 – Measuring Motion
motion: an object’s change in position relative to a reference point
- objects that appear to stay in place are called reference points (e.g. Earth, trees, etc…)
Speed Depends on Distance & Time
speed: the distance traveled divided by the time interval during which the motion occurred

2. Ch.5, Sec.1 – Measuring Motion
the SI unit for speed is meters per second (m/s)
- most moving objects do not move at a constant speed, so average speed is often calculated instead:
average speed = total distance
total time
Velocity: Direction Matters
velocity: the speed of an object in a particular direction
speed and velocity are different, as velocity must include a reference direction!!!
an object’s velocity changes if speed or direction changes

3. Ch.5, Sec.1 – Measuring Motion
see figure 4 on page 121 for combining velocities to equal resultant velocities
Acceleration
acceleration: the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change
the faster the velocity changes, the greater the acceleration is; the slower the velocity changes, the greater the deceleration is
- average acceleration can be found by using the following equation:
avg. acceleration = final velocity – starting velocity
time it takes to change velocity