1. Force:

* Net Force: The greater the net force acting on an object, the greater its acceleration, and thus the faster it will go. This is described by Newton's Second Law of Motion (F = ma).

* Direction of Force: A force acting in the same direction as the object's motion will increase its speed. A force acting opposite to the motion will decrease its speed.

2. Mass:

* Inertia: An object's resistance to changes in motion is called inertia. The more massive an object is, the more inertia it has, and the harder it is to accelerate. A larger force is needed to get a more massive object moving at the same speed as a less massive object.

3. Friction:

* Surface Friction: The force opposing motion between two surfaces in contact. Friction slows down an object. Rougher surfaces cause greater friction.

* Air Resistance (Drag): The force opposing the motion of an object through the air. This force increases with speed and surface area.

4. Gravity:

* Acceleration due to Gravity: On Earth, gravity pulls all objects downwards at a constant acceleration of approximately 9.8 m/s². This means that objects falling freely will continuously increase their speed.

5. Initial Speed:

* Starting Point: The object's initial speed can influence its final speed. An object starting from rest will need a greater force to reach a certain speed than an object already in motion.

6. Other Factors:

* Elasticity: The tendency of a material to return to its original shape after being deformed. A bouncy ball will lose speed less quickly than a clay ball when bouncing.

* Medium: The object's speed can be affected by the medium it is moving through. For example, a boat will move slower in water than a car on land.

It's important to note that these factors often work together in complex ways to determine an object's speed.