Why does your car take off slow then picks up?

Why does your car take off slow then picks up?
All internal combustion engines have what is referred to as a "power band." This is the part of the RPM range that the engine generates the most power. A cars power is rated in two main ways, torque and horsepower (kilowatts in some countries.) Torque is generated primarily at the low end of the RPM range, while horsepower is higher up. Cars that have smaller engines generate less torque and most of their power is in the top end of the RPM range. This means that they move more slowly when they first start moving and accelerate faster as the engine reaches higher rev's. Larger engines with more torque start out more quickly because they can access their power band earlier in the RPM range.