The phenomena of gravity, electricity, and magnetism are capable of acting over a distance to produce forces without direct contact between the affected objects. This remarkable behavior is called "action at a distance" and was a matter of considerable philosophical debate in Newton's time.

Note however, that these forces are still created by an object, on another object. That means that you must still be able to point to the object that makes the force. It is not correct for example to simply say that "Gravity pulled the ball down." You must note that it is the Earth that pulled the ball down using the gravitational force.

When making free body diagrams (FBDs) you must use this fact about the other body to help decide whether to include these forces. For example, if there are no magnets (or electromagnets) in the problem, you must not draw a magnetic force. Similarly, if you want to include weight in a problem, the Earth must be nearby. And whenever the Earth is nearby you must include weight.

Here are two common examples where students may go wrong.

The apparent weightleness in a falling elevator does not mean that weight is really missing. The Earth is nearby so weight must be included in the FBD. In fact, it is the cause of the downward acceleration.

The centrifugul sensation detected by our sense of balance when we travel in a car going around a corner, is not from a force outward. Here you cannot find an object that makes an outward force so none should be drawn. It is our inertia that carries us in a straight line and the car is actually turning away (inward) from underneath us. We appear to run into the side door, but in fact the door has run into us. No force outward, but (ultimately - we hope) a door force inward.