Extraordinary animations get the physics right.
What is a gas? What is a solid? How are solids and liquids different? Reading about it is not that informative. A picture is better but still doesn't explain well. One look at an animation tells the story in a way that immediately gets the big ideas across. Essential Physics is full of animations that are much deeper than just moving pictures. Each one is the result of many hours of careful research to be sure the physics is RIGHT and the learning objective is well met.