Acceleration is not constant when engines produce a constant force because acceleration depends on both the force applied and the mass of the object being acted upon. The relationship between force, mass, and acceleration is described by Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass.
Mathematically, Newton's second law can be written as:
F = ma
Where: F is the net force acting on the object, m is the mass of the object, and a is the acceleration produced.
When an engine or any other force-producing mechanism exerts a constant force on an object, the acceleration will vary if the mass of the object changes or if other forces act upon it. If the mass remains constant, the acceleration will be constant, as stated by Newton's second law. However, if the mass changes or if other forces, such as friction or air resistance, come into play, the resulting acceleration will be affected.
For example, consider a car with a constant engine force. Initially, when the car is at rest, the engine force accelerates it rapidly. However, as the car gains speed, air resistance and frictional forces become significant. These opposing forces act against the engine force and reduce the net force acting on the car. As a result, the acceleration decreases, and eventually, the car reaches a constant velocity where the net force becomes zero (assuming a balanced scenario without additional forces). In this case, the acceleration is no longer constant, even though the engine force remains the same.
Therefore, while a constant force can be applied by an engine, other factors such as mass, opposing forces, and changes in velocity will influence the resulting acceleration.