A change in speed or direction is known as acceleration. Acceleration is a vector quantity that describes the rate of change of velocity of an object. It is the change in velocity per unit time. The SI unit of acceleration is meters per second squared (m/s²).

There are three main factors that can change the speed or direction of a moving object:

1. Force: When a force is applied to an object, it can cause the object to accelerate. If the force is in the same direction as the object's velocity, the object speeds up. If the force is in the opposite direction of the object's velocity, the object slows down. If the force is perpendicular to the object's velocity, the object changes direction without changing speed.

2. Mass: The mass of an object can also affect its acceleration. The greater the mass of an object, the greater the force required to accelerate it. This is because it takes more energy to move an object with more mass.

3. Friction: Friction is a force that opposes the motion of an object. It can cause an object to slow down or even stop moving.

In addition to these three factors, there are other factors that can affect the speed or direction of a moving object, such as gravity, drag, and buoyancy.