# Gravity pulls or space presses

## Big Bang 4, textbook

105 44.2 Centrifugal force High centripetal forces are achieved through inclined positions. A curve is a change in direction and speed. This requires a force called the centripetal force. This is a reaction force that arises when cycling, for example, when the tires press diagonally against the ground. 44.2 Artificial gravitation Centrifugal force Now we finally come to the mysterious centrifugal force. This is very confusing - even for many physicists! A9 In chap. 44.1 you have heard that you only need a single force for a curve, which points to the center of the circular path, i.e. inwards. But when you drive around a curve in your car, you have the feeling that you are being pushed outwards! How does that fit together? A10 In scifi films one often sees space stations in which artificial gravity is generated by turning a huge ring (B 44.13). Can it work? And if so, how? Weightlessness prevails in space. In the rotating ring in the background, artificial gravity is generated by rotation. Is the? B 44.12 B 44.13 Now it's getting a bit tricky! Why don't you disappear into the ground even though the force of gravity is acting on you (A7; B 44.10 a)? Because the ground presses against you with the same force! Two forces of the same size, but directed in opposite directions, balance each other out exactly, and therefore you are not moving (b). But why does this force arise? Every force generates an equally large counterforce! That is what Newton’s third law says. You press against the earth and the earth presses against you. This counterforce can also be used to explain why you have to lie down in the curve (A6). A little preliminary consideration. Suppose you are pulling a rope. You press against the floor and the reaction force of the floor presses against you (B 44.11 a). Only the horizontal part of this force is important because only this helps pull the rope. The horizontal component corresponds to the shadow of the blue arrow when you illuminate it from exactly above. The harder you pull, the greater this force has to be, and the more obliquely you have to push yourself against the ground. In principle, it is the same with cycling (B 44.11 b). To get around a curve, you need a centripetal force. This occurs because you press the tire diagonally downwards against the ground and the ground diagonally upwards against you. The tighter the curve, the greater the centripetal force required and the more inclined you have to lie down. The same applies to all cornering movements on two legs or wheels, including running, inline skating or motorcycling (B 44.12). a) Usual, but actually incorrect representation b) Correct representation with force and counterforce B 44.10 Reaction force when pulling a rope (a) and cycling (b): The weight force is not shown. B 44.11 For testing purposes only - property of the publisher öbv