Principle objective of this lecture is to present on Gravity, Inertia and Friction. Gravity is a force pulling together all matter (which is anything you can physically touch). The more matter, the more gravity, so things that have a lot of matter such as planets and moons and stars pull more strongly. Inertia is a property of matter that causes it to resist changes in velocity. Inertia is a word we use when we talk about matter and movement. Friction is the restive force that occurs when two surfaces travel past each other.