Cadet Competition Written Practice Exam

What is the primary force that gives an orbit its shape?

1. Inertia

2. Magnetism

3. Friction

4. Gravity

The correct answer is: Gravity

The primary force that gives an orbit its shape is gravity. In an orbital system, such as the one involving planets, moons, and satellites, gravity acts as the central force that draws an object toward the body it's orbiting. This gravitational attraction keeps the object in a curved path rather than allowing it to travel in a straight line. An orbit is created when an object has a sufficient velocity to counteract the pull of gravity, resulting in a balance between the forward motion of the object and the inward pull of gravity. This dynamic creates an elliptical path, which is the shape of most orbits as described by Kepler's laws of planetary motion. The other forces listed do not have the same fundamental role in determining orbital shapes. Inertia describes an object's resistance to change in motion but does not account for the gravitational pull that dictates the curvature of an orbit. Magnetism, while a force with its own effects, does not play a significant role in celestial orbits. Friction is generally negligible in the vacuum of space, particularly concerning the motions of celestial bodies. Thus, gravity is distinctly the dominant force ensuring the stability and shape of orbits.