During the course of your 3D object design, you might require some knowledge you don't have, or perhaps have forgotten. Don't worry - there's a free service you can use to catch up: The Khan Academy.
It's a website jammed full of great short videos on a wide variety of topics, including many scientific areas possibly useful for 3D engineers: Chemistry, Biology, Linear Algebra, Trigonometry, Arithmetic, Precalculus, Statistics, Pre-algebra, Valuation & Investing, Probability, Algebra, Physics, Calculus, Differential equations and geometry.
There are 107 videos on Physics topics alone!
The site also includes many videos on standard test preparations and financial topics. From their tagline:
The Khan Academy is a not-for-profit organization with the mission of providing a high quality education to anyone, anywhere. We have 1000+ videos on YouTube covering everything from basic arithmetic and algebra to differential equations, physics, chemistry, biology and finance which have been recorded by Salman Khan.
Via The Khan Academy