For every action there is an equal and opposite reaction. And so say all of us. However, you don't need a detailed explanation from the Principia Mathematica to activate the legendary Newton's Cradle - the executive toy to end all executive toys. Just pull one of the outermost balls, gently release, and set a seemingly self-perpetuating cacophony in motion that has captured the imagination of generations. Tick... tick... tick... tick... tick... tick... there's a certain hypnotic rhythm to its greatness.

This full-scale replica of a modern day classic is not only the ultimate desktop timewaster - and a dashed retro-looking one at that - it's a fascinating insight into the very Laws of Motion themselves. Take for instance its practical demonstration of momentum conservation energy and pendulum simulation motion. It's brilliantly visually impactful. And truly fascinating to small - and not so small - boys. The Newton's Cradle might look like something that Reggie Perrin (or maybe even Heath Robinson) would be proud of. Yet, strangely, it has stood the test of time. It's timeless, perhaps, because it helps explain some of the basic laws of nature. And now its magical mind powers and universal Newtonian physics can be yours for the price of a brown beer voucher. Go on. Sir Isaac would be proud of you.