Answer:
Force.
Step-by-step explanation:
Let a is the acceleration of an object. It is given by the rate of change of velocity. Its formula is given by :

Also there is a relationship between the force and acceleration as per the second law of Newton. Its mathematical expression is given by :

m is the mass of the object
a is its acceleration.
It is clear that the acceleration of an object is directly proportional to the force. So, the acceleration of an object would increase if there was an increase in the force.