Final answer:
When you double Mass 1 while keeping distance constant, the mass increases by a factor of 2 and the gravitational force also doubles because it is directly proportional to mass.
Step-by-step explanation:
If you double Mass 1, keeping the distance (r) the same, Mass 1 has increased by a factor of 2. Consequently, the magnitude of the gravitational force between the two objects has also doubled. This occurs because the gravitational force is directly proportional to the mass of the objects involved and inversely proportional to the square of the distance between their centers. Even though the mass of only one object has increased, the increase in gravitational force occurs because the other mass and the distance remain constant in the calculation of gravitational force.