3
Ways to Accelerate Speed up…Slow down…or Change direction 
Average acceleration is the rate at which velocity
changes. Average acceleration is the change in velocity divided by an elapsed time. For
instance, if the velocity of a marble increases from 0 to 60 cm/s in 3
seconds, its average acceleration would be 20 cm/s/s (or 20 meters per second,
for every second it travels) . This means that the marble’s velocity will increase by 20 cm/s every second. See the table below: 
Time (Seconds) 
Velocity (cm/s) 
0 
0 
1 
20 
2 
40 
3 
60 
4 
80 
Here is the formula we will use: 
Average Acceleration = Velocity Time 
= “change in” or “difference of”
Here is another way of looking at the formula: 
Average Acceleration = 
_{} Velocity = v_{2} –
v_{1} _{} Time t_{2} –
t_{1} 
Where V_{2}
is the Final Velocity and V_{1}
is the Starting Velocity and
t_{2} is the Final Time and t_{1}
is the Starting Time
Sample
problem) At 12:00, a
rocket begins to accelerate from 20 mph. At 12:05 the rocket is traveling at
280 mph. What is the acceleration of the rocket? 
Average Velocity = 
_{} Distance = d_{2} –
d_{1} 
= 280 mph – 20 mph 
= 260 mph 
= 52 mph/min 

_{} Time t_{2} –
t_{1} 
5 min – 0 min 
5 min 
