* Astronomy

Newton's second law of motion, that pillar of classical physics, the formula that says the force on an object is proportional to acceleration, has now been tested, and found to be valid, at the level of 5 x 10^-14 m/s^2. This is a thousandfold improvement in precision over the best previous test, one carried out 21 years ago (Physical Review D, vol 34, p 3240, 1986). The new test was performed by physicists at the University of Washington using a swivelling torsion pendulum, a special kind of pendulum in which the restoring force is not gravity (as you would have in a hanging pendulum) but is provided by a very thin torsion fibre.

Read more