# What do you mean by acceleration 1

## Big Bang HTL 1, textbook

9nf8b9 Selected phenomena 21 Straight movements 4 Velocities are also relative (F4)! How big they are measured is a question of the reference system (see also F9, Chapter 4.2). From your point of view, a cup at the table in the plane does not move, from the point of view of a person on the ground at 250 m / s. Which view is correct? Both! It's just a question of the frame of reference! By the way: If you think that you are sitting quietly in the armchair right now, then that is also a matter of opinion. You are at rest relative to the earth! But the earth itself moves at 30 km / s (!) Around the sun! So from the point of view of the sun, you're at a blazing pace. Relative quantities always need a comparison to determine them. You cannot determine it alone. That's the whole point! If you are flying in the deepest universe, where there are no points of comparison (e.g. a planet), you cannot tell whether you are moving (F5). And if another spaceship flies past you, then you can only determine how great the speeds are relative to each other. But you cannot say "I am in peace and the other one flies past me" or vice versa. This is different with accelerations (i.e. changes in speed). Accelerations are absolute (F3). Absolute means "detached". So you don't have to compare. When you sit in an airplane that is accelerating, you can feel it and of course measure it. You can measure acceleration all by yourself in the deepest universe, without any reference point. If no accelerations occur in any form, then one speaks of an inertial system in physics. So one can say: If you are in a completely calmly flying airplane, then you are in an inertial system. Everything works normally in these systems. When the aircraft speeds up or slows down, it is no longer an inertial system. You can feel that too. It could then be that the coffee spills over or you miss the cup with the sugar lump (Fig. 4.4). Summary The unaccelerated speed is something very special. If you move uniformly, you don't notice it. You are then in an inertial system and everything works normally. You need a point of reference, something second, to determine this form of movement. That makes the speed relative. But accelerations are absolute. You can measure and feel this without having to compare. Fig. 4.4: If the aircraft changes its speed, accelerations occur. Z 4.2 To the edge of the galaxy Description of the speed This section deals with the mathematical description of the speed, and we take another short excursion into Einstein's world. Two cyclists drive towards each other at 10 km / h. When they are exactly 10 km apart, a fly starts at 30 km / h from the front wheel of the right driver, flies to the front wheel of the left driver, back again, and so on. How far does it go before the riders meet in the middle? Mr. Müller goes for a walk with his dog. In which direction (forwards, sideways, ...) does he have to throw the stick so that the dog covers as much distance as possible during the walk? L If you count the seconds between lightning and thunder and then divide by 3, you know how many km the lightning was gone! So how great is the speed of sound? You drive in a convertible at 5 m / s and throw a ball forward at 10 m / s (Fig. 4.7 a). How fast is the ball from the point of view of an observer standing on the ground? You fly a spaceship at half the speed of light (c / 2) and send out a beam of light to the front (b). How fast is the light beam from the point of view of an observer on earth? F6 A2 Fig. 4.5 F7 A2 Fig. 4.6 F8 A1 F9 A1 Fig. 4.7 For testing purposes only - property of the publisher öbv