piconewtons

Piconewton, denoted pN, is a unit of force equal to 10^-12 newtons. The term combines the SI prefix pico- with the Newton. In practice, piconewtons describe forces typical of molecular-scale phenomena, such as interactions within biomolecules and nanoscale motors.

Because these forces are very small, pN-scale measurements are common in biophysics and nanotechnology. Techniques such as optical tweezers, magnetic tweezers, and atomic force microscopy are used to apply and measure forces in the pN range.

Typical values: Motor proteins like kinesin stall around five piconewtons; single-DNA force experiments reach tens of piconewtons; protein unfolding forces can range from a few to tens of piconewtons. For context, 1 pN acting over 1 nm corresponds to about 1x10^-21 joules, roughly a fraction of kBT at room temperature (kBT ~ 4.1x10^-21 J).

In precision measurements, experimental calibration may convert instrument response to pN, using known force standards.