 Distance vs. Displacement  Speed vs. Velocity

 Acceleration  ◦ The rate at which velocity changes  We typically think of acceleration as speeding up (getting faster), but it also means slowing down (getting slower) or changing direction.

 Is a vector quantity ◦ Which means its direction matters  Positive acceleration means your velocity is becoming more positive. ◦ Could either mean speeding up, or turning towards the positive direction, or slowing down while traveling in the negative direction.  Negative acceleration (sometimes called deceleration) means your velocity is becoming more negative ◦ Could either mean slowing down or turning toward the negative or speeding up in the negative direction

 Is measured in meters per second per second or meters per second squared.  The formula for acceleration is… a = v f – v i ΔtΔtΔtΔt  Since velocity is measured in m/s and time in seconds… a = m/s – m/s = m/s s s m/s 2

 A car driving at 25 m/s slams on the brakes and slows to a stop in 3.6 seconds. What is the car’s acceleration? G  v i = 25m/s v f = 0.0 m/s Δt = 3.6s U  a = ? E  a = (v – v o )/t S  no algebra required for this one S  a = (0m/s – 25m/s)/3.6s a = -6.9m/s 2

 v f = final velocity  v i = starting velocity  d = final position (displacement)  a = acceleration  Δt = time

Bob starts at rest and runs with a constant positive acceleration of 4.5m/s 2. What is Bob’s velocity when he is 52m from where he started?