On this day in physics: 03 February 1966- The Soviet Luna 9 Spacecraft landed on the moon, making it the first "soft landing" on a non-earthen body in human history. A soft landing is a controlled landing (i.e. not a crash) where there is no major damage to the craft. The probe was unmanned, it did contain a camera to take pictures which were sent back to earth until 6 February when the batteries finally died. [Source].
Word of the Day: Inertial Reference Frame- An inertial reference frame is one that is not accelerating. It is a theoretical construct, but very useful in the theory of relativity. Imagine yourself right now, sitting. To you, you're not moving, even if you're driving, or riding, or running, or walking. But, for this argument, let's say that you are sitting, totally still. You're holding a ball (why not) and decide to throw it. Once it's thrown, it is subject to the acceleration of gravity, and so if you're the physics type, you'd be able to do some calculations about its motion, and would be able to say for certain that from your inertial reference frame of not moving, that the ball had a certain velocity, a certain acceleration, etc. And all those calculations are totally valid considering your perspective of being totally motionless, but then remember that you're on a planet, spinning around its axis, which is revolving around the sun, which is in an arm of a spiral galaxy. So you're not really stationary. But, theoretically you're totally still. If you were to be sitting on the couch, and in front of you there was an elevator which was to be rocketed upwards exactly opposing the acceleration of gravity. Once the rocket launched, someone inside the elevator would have a perceived weightlessness, and there is no experiment that could be done from within the elevator to find out if he was truly motionless, or undergoing correspondingly opposing accelerations. If you were to leave earth's atmosphere, and enter a truly weightless environment, far from the shackles of planetary gravity, and the rocket were to continue accelerating at the same rate of gravitational acceleration, 9.81 m/s^2, anyone inside the elevator would feel as though they were standing on Earth, and they would not be able to tell if they were being accelerated by a rocket, or if they were being gravitationally attracted by a mass. This led Einstein to the conclusion that mass warps spacetime. The problem is that there is no truly inertial reference frame from which all measurements can be made, because something is always moving with respect to something else, or so we believe in 2016. Tune in in 100 years to see if this podcast still holds water.
Quote of the Day: "Nothing happens until something moves."- Albert Einstein [Source]
Keywords: Inertial, Reference, Frame, Space, Time, Acceleration, Gravity.
