The force described in law 1 is inertia. Inertia is an object's tendency to stay at rest or in motion. The larger the object, the greater the inertia, both ways. If you are pushing a heavy box up a hill, more energy is required to put the box in motion. Once in motion, the box is easy to push or pull. If it slides down the hill, it is hard to stop because it is already in motion (although gravity plays a part in its motion down the hill).

The "other force" described in law 1 is friction. Friction is what causes objects to eventually slow down and stop. It occurs when two surfaces contact each other, and does happen with air (when it happens with air it is known as "drag"). An object only continues to move in a vacuum, such as in space, where there is no air and no friction.

Gravity is a universal phenomenon, felt even in space. On a planet, gravity pulls all objects toward the center of the planet, effectively keeping them on the ground. It is not limited to this definition, however. Gravity is a force exerted by objects upon other objects that causes two objects to attract to one another.

All objects have something called "momentum," the product of mass multiplied by velocity. Mass is the overall size of an object - its weight and size measurements (a bowling ball has more mass than a tennis ball). Velocity is an object's speed.

The Earth philosopher Aristotle first posed the idea that heavier objects fall faster than lighter ones. The renaissance scientist Leonardo da Vinci thought that objects fell in proportion to the distance they have fallen, but it wasn't until the 17th century that astronomer Galileo Gaileli got it right - small and heavy objects fall at the same speed. The proportion is how long objects have been in the air. When objects have been in the air for a long time, only then do heavier objects' momentum begin to act and they land before lighter objects.

In the 1930s, Albert Einstein proposed that space was curved and because of this, light also curved. This was his general theory of relativity. His special theory, known widely because of its application to warp power, is that energy = matter times the speed of light squared (E=MC²). It means that as one gets closer to the speed of light, energy consumption increases along with the momentum of the matter going at the speed of light.

An offshoot of Einstein's special theory is that, as objects approach the speed of light, time begins to slow down for them because they are going so incredibly fast. As a result, an object at near-light speed can be in motion for a year while it seems that dozens of years have passed to an object at "normal" speed. This is why impulse power is limited to 0.25c or at the most, 0.5c and why starships do not travel for extended time at impulse speed. Traveling any faster at sublight, or for longer amounts of time, will result in an increased time dilation effect.