 Acceleration is the rate that velocity changes over time.  An object is accelerating if ◦ Its speed changes ◦ Its direction changes ◦ Both its speed and direction change

 Speeding up ◦ From red light to green light ◦ When you are in a car as it speeds up, your body goes backward.  Slowing down ◦ From green light to red light ◦ When you are in a car as it slows down, your body goes forward.

 The variable for acceleration is “a.”  a = Δv / t  The units for acceleration are m/s 2  If the object’s acceleration is negative, the object is probably slowing down.

 A car can get from rest to 27m/s (around 60mph) is 2.5seconds. What was the car’s acceleration? Given: V i = 0 V f = 27m/s t = 2.5s a = (v f – v i ) / t a = (27-0) / 2.5 a = 27 / 2.5 a = 10.8m/s 2

 Page 375: #1-5  SHOW YOUR WORK!!

 Before, we used v = d / t, or d = v x t  This equation only works if velocity is constant (not changing)  By definition, velocity changes if an object is accelerating.

 If an object is speeding up, ◦ It covers a distance of  V x t plus a little bit.  If an object is slowing down, ◦ It covers a distance of  V x t minus a little bit.

 Instead of the equation we learned when velocity was constant…  We use the following equation when accelerating,  d = v i t + ½ at 2

 Example: A runner accelerates at 1.2m/s 2 for 30seconds at the beginning of a race. How far does he travel in those 30 seconds? d = v i t + ½ at 2 d = 0 + ½ (1.2)(30) 2 d = 540m Given: a = 1.2m/s 2 t = 30s V i = 0