What comes to your mind when you see or hear the word physics? Believe it or not, but physics is in everything around us. We use physical concepts in almost everything we do. Physics is so important that it is even considered to be the basis for all other sciences. Physics by Demonstrations is a free online interactive learning/teaching tool. As the name implies, this site lets the user learn or teach physics not just by theories but also by visual demonstrations. With our site users can learn/teach basic and not so basic concepts of physics, run interactive Java simulations, watch animations, and have fun while learning or teaching. The site is broken down into five main sections: mechanics, fluids, waves, electricity and nuclear physics. We suggest you to examine them in the order given. However, feel free to examine the sections in any order you want.