# What force does gravity repel?

## Big Bang Physics 6, textbook

Basics of Electricity 1 22 GG 6.2 / G 6.2 Electricity / Electrical Energy 73 Which charges are transferred when rubbing (F5)? Only negative! Why? Because it is impossible to remove protons from the nucleus by rubbing. However, electrons can be detached from the shell relatively easily. The spoon in Fig. 22.5b, p. 71 has an excess of electrons and the cloth a deficiency of electrons. You can see that something can be positively charged, even if only electrons are flowing. Summary Like matter, the charge cannot be divided at will. Protons and electrons have the smallest, freely occurring charge, and they are called the elementary charge. 22.1.3 Trillion Electrons The Coulomb's Law This section deals with the law that describes the forces between charges: the Coulomb's law. Before we look at the forces between charges, let's take a quick look at the charge itself. The unit of charge is the coulomb (C). It is not used in everyday life and it is not easy to imagine something under it. But one can say like this: A full battery has a charge of a few to many thousands of coulombs (see Fig. 22.10 and Tab. 22.4, p. 76). Because the elementary charges are so tiny, it is impractical to give the number of individual charges. Info: 6 trillion electrons Although several researchers succeeded in establishing a law for electrical force, it is attributed to the French CHARLES AUGUSTE DE COULOMB, after whom the unit of charge is named. He formulated it around 1776, and it applies between two point-shaped or spherical charges. The equation is the Z What is NEWTON's law of gravity? Do some research and look it up! With what electrical force do the proton and the electron in the hydrogen atom attract each other? With what force do the two protons in a helium nucleus repel each other? Could you use muscle power to detach the electron and hold the protons together? Submit a tip! L Two electrons are at a distance of one meter. They attract each other through gravitational force, and repel each other through electrical force. What power is gaining? How does a laser printer work? Are the letters burned onto the paper with a laser? F6 W1 F7 W2 F8 W1 F9 S2 Very similar to law of gravitation published by SIR ISAAC NEWTON in 1686. Formula: electrical force (Coulomb's law) FE = k Q 1 Q 2 ____ r 2 FE… electrical force 620 Q 1 and Q 2… charge of objects [C] r… distance between charges [m] k… constant of proportionality k = 8.99 · 10 9 Nm 2 / C 2 Despite many similarities between the two laws, there are also two essential differences (see Tab. 22.1). First, the electrical force is much, much greater than the force of gravity. It is the second strongest of the four forces in the universe, whereas gravitational force is the weakest. The second big difference: while masses can only attract each other, charges can also repel each other. electrical force gravitational force F E = k Q 1 Q 2 ____ r 2 F G = G m 1 m 2 _____ r 2 proportional to 1 / r 2; therefore acts infinitely proportional to 1 / r 2; therefore acts infinitely proportional to the product of the two charges proportional to the product of the two masses k can only be determined experimentally (8.99 · 10 9 Nm 2 / C 2) G can only be determined experimentally (6.67 · 10 –11 m 3 / (kgs 2)) unequal charges attract each other, identical charges repel each other Masses can only attract each other relative strength 10 –2 relative strength 10 –38 Tab. 22.1: Similarities and differences between FE and FG: The relative strength applies in Comparison with the strong force that holds the quarks together in the neutrons and protons (see Tab. 10.1, Chapter 10.1, "Big Bang 5"). Info: who is stronger? | -> p. 74 Experiment: Electroscope and Co. | -> p. 74 Info: Laser printer | -> p. 74 6 trillion electrons How many electrons do you need in a pile to get a charge of one coulomb? Or to put it another way: by what number do I have to multiply the unit charge e to get 1 C? N · e = 1 C. It follows that N = 1 C / e. N is numerically the reciprocal of the elementary charge and thus around 6.2 · 10 18. Wow! For one coulomb you need more than 6 trillion electrons. So it's no wonder that you don't state the number of electrons. i Fig. 22.10: A type AA alkaline battery has around 4000 coulombs when charged. F For testing purposes only - property of the publisher öbv