Is burt bread physical or chemical change

-- When acceleration is zero, the object is moving at a constant, unchanging speed (and in a straight line).

-- When acceleration is positive (more than zero), the object's speed is growing.  It's "speeding up".

-- When acceleration is negative (less than zero), the object's speed is shrinking.  It's "slowing down".  Some people call this "deceleration", but it's just negative acceleration.