Acceleration is a vector quantity that is defined as the rate at which an object changes its velocity. An object is accelerating if it is changing its velocity.
And as others have said, change in direction is still acceleration. That's part of Newton's (apocryphal?) apple story --- he witnessed an apple falling, and wondered why the moon doesn't also fall. His amazing insight is that it does fall (accelerate), it's just that it falls in such a way that it orbits, rather than hits, the Earth (for timescales relevant to a human).
Agree 100% on the dead petal. Every manual transmission ive owned has the clutch and a footrest, so it actually appears to be 4 pedals if you dont know what youre looking at