motion

=Always Moving--Physics4Kids.com= Motion is one of the key topics in physics. Everything in the universe moves. It might only be a small amount and very slow, but movement does happen. Don't forget that even if you are standing still, the Earth is moving around the Sun and the Sun is moving around our galaxy. The movement never stops. Scientists also use the term **mechanics** to describe motion. Over the years, scientists have discovered several rules or [|laws] that explain all motion you might find. There are also special laws when you reach the [|speed of light] or when physicists are look at **atoms**.

=Speed it Up= The physics of **motion** is all about forces. [|Forces] need to act upon an object to get it moving. Motion won't just happen on its own. So how is all of this motion measured? Physicists use some basic terms when they look at motion. [|Velocity] is a value for the basic speed of an object. That speed is achieved after the action of a force. **Acceleration** is a twist on the idea of velocity. Acceleration is a measure of how much the velocity of an object changes. Velocities could either increase or decrease over time. **Mass** is another big idea in motion. Mass is the amount of something there is in grams (or kilograms). A car has a greater mass than a baseball.

=Simple and Complex Movement= There are two main ideas when you study mechanics. The first idea is that there are **simple movements**, such as if you're moving in a straight line, or if two objects are moving towards each other. Ideas like acceleration and velocity are simple ideas to physicists. A lever is also a good example of simple motion. A lever has a force applied to one end of a pole and the other end moves in the opposite direction. The amount of force and distance from the fulcrum tells you how much the rod will move.

There are also more **complex movements** for which not all of the laws apply. Ideas like work or complex combinations of forces fall into this category. These examples stretch the limits when you learn about mechanics. Examples of complex motion include motion that happens in a circular direction. You might be looking at **angular acceleration** or **centripetal forces** as you spin a ball that is tied to a string. Even [|electrical charges] fall into the category of complex motion in physics