Here's why:

* Newton's Second Law of Motion: This law states that the force (F) acting on an object is equal to its mass (m) multiplied by its acceleration (a): F = m * a

* Constant Acceleration: If acceleration is held constant, the equation becomes: F = m * (constant)

* Direct Proportionality: This means that force is directly proportional to mass. If you double the mass, you double the force required to maintain the same acceleration. If you halve the mass, you halve the force.

In summary: When acceleration is constant, a heavier object requires a greater force to achieve that acceleration compared to a lighter object.