On this day in physics: 28 January 1613, the planet of Neptune may have been discovered, unbeknownst to its observer, Galileo Galilei. According to his observation records of that night, he noticed what he believed to be a star, very close to the planet Jupiter. This star does not match any current records. For three nights it was observed, and then had moved to an unobservable part of the sky. Neptune remained under the radar for another 233 years, until it was formally discovered as a planet by Urban Le Vernier, who predicted its existence using only mathematics, and by Johann Galle, an observational astronomer who actually first found it in 1846. Neptune's year is 164.8 earth years long, meaning that since we've first discovered it has only gone around the sun once (2011!) plus a very little bit.
Word of the Day: Inertia can be embodied by the following phrase: "A body at rests remains at rest." Inertia is an objects opposition to motion, or its desire to remain inert. It is also responsible for "A body in motion tends to remain in motion unless acted on by an outside force" (courtesy Isaac Newton). So, if we have an object "at rest" or not moving, we will not see this object move unless something happens to it which would induce motion, such as a wind, push, or other action. And, if this motion were to occur in a deep space vacuum (we're going to ignore air resistance here), it would continue to move along with a constant velocity, until something were to stop it. These properties are referred to as inertia. When you get in your car, and finally turn on the highway, getting on the on ramp, starting at a presumable 0 mph, your car's engine must burn a considerable amount of gas to get us up to the 65mph speed limit, and what the engine is doing is overcoming the inertia of the car, or its desire to remain at its 0mph velocity. Once on the highway, we still need to have our foot on the gas, but we're burning considerably less gas. In a frictionless and air resistance less world, we wouldn't need to have our foot on the gas at all, we'd just cruise along forever, although braking would be something of an issue. On the highway, the only energy expenditure of gas is to overcome the resistive friction of your tires on the road, because once in motion, the car's inertia wants to keep it going at whatever speed you've set.
Killer Resource: What if the moon was replaced by various planets visualized.
Keywords: Inertia, Mass, Velocity, Car, Friction, Highway, Neptune
