The amount by which speed increases in one second is called acceleration.

Here's why:

* Speed: Speed is how fast something is moving. It's measured in units like meters per second (m/s) or kilometers per hour (km/h).

* Acceleration: Acceleration is the *change* in speed over time. It's measured in units like meters per second squared (m/s²).

Example:

* If a car starts at rest (0 m/s) and increases its speed to 10 m/s in 2 seconds, its acceleration is 5 m/s². This means its speed increases by 5 meters per second *every* second.

Important Note: Acceleration can also mean slowing down (deceleration). In this case, the change in speed is negative.