A computer simulation is an attempt to model a real-life situation on a computer so that it can be studied to see how the system works. By changing variables, predictions may be made about the behaviour of the system.
Computer simulation has become a useful part of modeling many natural systems in physics, chemistry and biology, and human systems in economics and social science (the computational sociology) as well as in engineering to gain insight into the operation of those systems. (Source: Wikipedia)

PMI on Computer Simulations in Education
Plus: Use real-life systems or processes but they have been simplified to focus on the key educational outcome
More details:
Computer simulations provide science students with theoretical or simplified models of real-word phenomena—for example, a frictionless world where the laws of Newtonian physics are more apparent—and they invite students to change features of the models so that they can observe the results. Science teachers use simulations in a variety of ways. They can use them to prepare students for future learning, or they can use them to supplement or replace other expositions on a topic. For example, a teacher might use a simulated frog dissection as a preparation for an actual dissection or as a substitute for the dissection. Science teachers can also use simulations to help students integrate facts, concepts, and principles that they learned separately. For example, students might play the role of world leaders or citizens in other countries in a simulation designed to help them apply their learning to realistic problems. (Source:
Minus: There is not alot of quantitative research that supports their effectiveness with respect to improving educational outcomes but there is quite substantial evidence in the qualitative realm.
Interesting: A area of continual growth since the late 1980s.

Science Simulations
Explore Learning - Gizmos -
Crocodile Clips Science Player - with 8 excellent and FREE simulations (must register) -
3-D interactive science simulations from Prentice Hall Publishing -
Absorb (Yenka and Crocodile Clips conbined) -
These resources include Maths, Physics, and Chemistry Resources for FREE

Biology Simulations
Cells Alive -
Visible Human (Java Required) -
Plant and Animal Cells in 3D -

Chemistry Simulations
Chemistry Experiment Simulations - 40 downloadable simulations for Year 11 and 12 students
Virtual Lab -
Flash Files of various chemical identification methods from atomic absorption through to gas chromatography

Physics Simulations
Minds on Physics -
Math Physics and Engineering Simulations -
Applet Collection (Java Required) -
Paul Falstad's Physics Website -
Trebuchet Simulations - - two variables - six variables - 3D graphics with several variables

Earth Science - Simulations
Astronomy Interactives -
Geology Online Labs -