# Ram pressure

Ram pressure stripping in NGC 4402 as it falls towards the Virgo Supercluster (off image, bottom left). Note the dust (brown) trailing behind the galaxy.

In physics, ram pressure is a pressure exerted on a body which is moving through a fluid medium. It causes a strong drag force to be exerted on the body. It is given by:

$P= \rho v^2$ [1]

where P is the pressure, $\rho$ is the density of the fluid and v the velocity of the body. Alternatively the body can be stationary and v describe the velocity of the fluid, e.g. the solar wind.

For example, a meteor traveling through the Earth's atmosphere produces a shock wave generated by the extremely rapid compression of air in front of the meteoroid. It is primarily this ram pressure (rather than friction) which heats the air which in turn heats the meteoroid as it flows around it.[2]

Galaxies in clusters experience ram pressure as they move through the intracluster medium; it is capable of stripping the galaxy of much of its interstellar gas.[3]

## Notes

1. ^ Relativistic Astrophysics and Cosmology, A Fabian and Lasenby, University of Cambridge Lecture Notes, Michaelmas 2010.
2. ^ Plait, p.1
3. ^ Grebel, Gallagher, Harbeck, pp.1-15