In physics, we take measurable quantities from the real world, and attempt to find meaningful relationships between them. A basic example of this would be the physical ideal of {{CMD_7}}. Force applied to an object changes the motion of an object. Here's the deal though, at a basic level {{MATH_8}} and while we can put a physical interpretation to this arithmetical definition, at the end of the day force is simply ``mass times acceleration.'' The SI unit of force is a {{CMD_9}}, which is defined to be {{MATH_10}} {{CMD_11}} To get a feel for what a newton is, consider this: if an apple has a mass of {{MATH_12}}, what force would an apple exert on your hand due to the acceleration due to gravity? {{CMD_13}} {{MATH_14}} {{CMD_15}} {{CMD_16}} Hence the ``weight'' of an apple is approximately {{MATH_17}}. {{CMD_18}} {{CMD_19}}