Density is a measure of the mass of an object per unit volume; thus, it has units of
mass divided by length cubed such as kilograms per cubic meter (kg/m ) or pounds
per cubic foot (lbs/ft ).
15 lbs/5 ft = 3 lbs/ft
Velocity is the change in length per unit time; thus, it has units such as kilometers per
hour (km/h) or feet per second (ft/s).
Acceleration is a measure of the change in velocity or velocity per unit time; thus, it
has units such as centimeters per second per second (cm/s ) or feet per second per
second (ft/s ).