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I've come to understand that lateral and sideways can be used when moving a forward-facing object from one side to another (and eventually back again).
Is there a common word for forward and backward movement, without specifying which?
Example:
A car cannot make lateral movements, only {forwards and backwards}.
(I hope I am using lateral correctly; please point it out if not.)
Axial would come closest. It can mean "along the axis (of an object)".
If something can only move forwards or backwards, or the direction doesn't matter in general, then the movement is simply a movement. No attribute required.
The orientation of the object (e.g. forward-facing) doesn't matter by the way because lateral is relative to it (or you).
The word you're looking for is longitudinal. (Wikipedia: Aircraft Principal Axes)
Which is defined as: (Google: define longitudinal)
- running lengthwise rather than across
For surface movement, lateral and longitudinal are perpendicular. To create 3D movement just add the vertical axis for vertical movement. This axis is also needed to describe left and right rotation, or yaw. (Wikipedia: Yaw Rotation & Road Vehicles)
Therefore your original example becomes:
A car can only move longitudinally (forward & backward) with varying amounts of yaw (turning left and right), and is incapable of moving laterally (left & right) in normal operating conditions.
Most folks would just use both words in such an instance: "forwards and backwards" - as they are two different directions, and not everything can do both of them.
Although, if you are telling someone to move a car stuck in the snow, you could use "rock": (we probably got it from 'rocking chair') it means "move it backwards, then, forwards (repeatedly)." (And it saves you from yelling, "Put it in Drive and hit the gas... Now put it in Reverse and hit the gas..." over and over.) (US)
The terms surge, sway, and heave are used by engineers to describe displacements (often perturbations) with respect to the x, y, and z body axes. If a body is only free to move along the x axis, then it is constrained in sway and heave. You may want to place constraints on rotation as well. Typical dynamic analysis of free bodies will have a state vector for the position, velocity, and acceleration for each of the six degrees of freedom. When you start using multiple frames of reference, the variable list can get pretty obnoxious.
Fast or quick the idea of fastness.
You can move a car laterally, but it's called drifting. If you push on a car in neutral in the fast direction it goes faster than if you pushed it from the slow direction.
