Your child will learn...GravityGravity is a force of attraction that exists between any two masses, any two bodies, any two particles. It is an attraction that exists between all objects, everywhere in the universe. Solar System and SpaceThe Solar System is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly. SpoolSpool is the combination of an engine compressor and high-pressure turbine that drives it using a connecting drive shaft. In a dual-spool engine, the compressor and high-pressure turbine are both split into two segments.