Here's why:

* Newton's Second Law of Motion: This law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, this is expressed as:

F = m * a

Where:

* F = Force

* m = Mass

* a = Acceleration

* Direct Proportionality: This means if you double the force (F) while keeping the mass (m) constant, you will double the acceleration (a).

* The Key Condition: The statement "Twice the force results in twice the acceleration" is only true if the mass of the object remains constant.

Example:

* If you push a 10 kg box with a force of 10 Newtons, it will accelerate at 1 m/s².

* If you double the force to 20 Newtons (and keep the mass at 10 kg), the acceleration will double to 2 m/s².

However, if you change the mass, the relationship changes.

* If you double the mass of the box to 20 kg while keeping the force at 10 Newtons, the acceleration will be halved to 0.5 m/s².

In conclusion:

The relationship between force and acceleration is directly proportional, but only if the mass of the object remains constant. If the mass changes, the relationship is no longer a simple doubling or halving.