Which of the following is not a characteristic of alternating current?

Alternating current (AC) is characterized by the flow of electric charge that periodically reverses direction. This means that AC is defined by its ability to switch direction, which is a key distinction from direct current (DC), where the flow moves in one constant direction. While AC can provide heat through various applications and can be used to stimulate the skin, it is the ability to switch direction that fundamentally distinguishes it among types of electrical currents.

The other options encompass attributes related to AC. Providing heat is a characteristic of AC due to its ability to deliver a significant amount of energy, which can create thermal effects in conductive materials. Similarly, AC can stimulate the skin as it allows for the flow of current through conductive mediums, facilitating various skin treatments.

Thus, the correct concept regarding alternating current is that it does indeed switch direction, and it does not solely move in one direction, which makes the identification of the characteristic that does not apply to AC clear.