‫Welcome back, and here you have the answers.
‫This is your first position vector for June one and this is your second position vector for June two.
‫As you can see, you have to pay attention to the direction of each inertial frame dimension in order
‫not to mess up the plus and minus signs.
‫And also, I could have put that inertial frame in any other place.
‫I could have put it here or here or here or even here.
‫And with each choice, the position vectors would have been different because you would be measuring
‫the distances from a different location.
‫Now, there is one final remark that I want to make about the inertial frames.
‫When we say that an object moves with respect to an inertial frame, it means that the object moves
‫along with the body frame and the inertia frame is fixed to the ground or to the building or wherever
‫you fix it to.
‫So the initial frame is not moving.
‫However, then you could say that, OK, but the ground is not fixed because the ground is on the planet
‫Earth and the planet Earth rotates.
‫So why wouldn't we use the center of the Earth as our inertial reference frame?
‫However, the Earth rotates around the sun and the sun rotates around the black hole in the middle of
‫the Milky Way galaxy, and even our galaxy moves with respect to other galaxies.
‫So it seems that in our universe there is nothing fixed.
‫Everything moves.
‫But the point is what moves with respect to what if I put my reference frame onto the ground and fix
‫it to some kind of location, then yes, that location moves with the earth, but so does the car and
‫the drone when they are completely at rest.
‫When the drone or the car, when they don't move at all, then their location with respect to that inertia
‫frame location doesn't change.
‫And both the inertial frame and then the body frame attached to a drone or a car or or another object,
‫all of them rotate around the center of the earth and around the sun and around the center of the galaxy
‫and with respect to other galaxies.
‫So it's all about what moves with respect to what.
‫And depending on the problem that you have to solve, you have to find for yourself the most convenient
‫location for your inertial reference frame.
‫If you have a car that wants to change the lane or you have a drone that wants to fly close to you,
‫then choosing some kind of ground location for your inertial frame that is close to that car or drone
‫makes sense.
‫But of course, if you have a long distance flight with an airplane or a satellite orbiting the Earth,
‫then perhaps it is better to choose the center of the Earth as the location for your inertia frame.
‫And if you have interplanetary travels, then perhaps the center of the sun could be a good place for
‫that.
‫So it all depends on the problem that you have to solve.
‫And then you choose a location for your inertia frame, which makes sense and which is suitable for
‫that specific problem.
‫So that's what I wanted to mention.
‫And now in the next video, we're going to start talking about rotation matrices.
‫Thank you very much.
‫And see you there.