It would travel indefinitely in a straight line.
Explanation
Galileo’s experiments with inclined planes were fundamental in formulating the concept of inertia, which later formed the basis of Newton's First Law of Motion. Galileo studied the motion of objects on two inclined planes placed facing each other.
Analysis of the Experiment:
Galileo observed that when a marble rolls down one inclined plane, it climbs up the second inclined plane to reach nearly the same vertical height from which it was released. The distance traveled on the second plane depends on its angle of inclination:
- If the slopes are equal, the marble reaches the same height at the same distance.
- If the slope of the second plane is decreased, the marble travels a longer distance to reach the original vertical height.
- Limiting Case (Zero Slope): If the slope of the second plane is reduced to zero, the plane becomes horizontal. In this scenario, the marble can never reach the initial vertical height. Consequently, in an ideal situation without friction, the marble would continue to travel indefinitely in a straight line with uniform velocity in an attempt to reach that height.
Key Takeaway:
Galileo concluded that the state of rest and the state of motion with constant velocity are equivalent. An object requires no external force to maintain its motion in a straight line unless acted upon by friction or another unbalanced force.