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It’s not correct to say that the moon orbits the earth; rather, both the earth and the moon move in orbits around their common center of mass.
neden kemerinizi yukarı çekerek havalanamazsınız? çünkü:
When a body or a collection of particles is acted on by external forces, the center of mass moves as though all the mass were concentrated at that point and it were acted on by a net force equal to the sum of the external forces on the system.
This result is central to the whole subject of mechanics. In fact, we’ve been using this result all along; without it, we would not be able to represent an extended body as a point particle when we apply Newton’s laws. It explains why only external forces can affect the motion of an extended body. If you pull upward on your belt, your belt exerts an equal downward force on your hands; these are internal forces that cancel and have no effect on the overall motion of your body.
Coulomb established what we now call Coulomb’s law:
The magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. In mathematical terms, the magnitude F of the force that each of two point charges q1 and q2 a distance r apart exerts on the other can be expressed as
F = k. |q1 q2|/r^2 (21.1)
where k is a proportionality constant whose numerical value depends on the system of units used. The absolute value bars are used in Eq. (21.1) because the charges q1 and q2 can be either positive or negative, while the force magnitude F is always positive.
Most of the forces on (...) water skier are electric. Electric interactions between adjacent molecules give rise to the force of the water on the ski, the tension in the tow rope, and the resistance of the air on the skier’s body. Electric interactions also hold the atoms of the skier’s body together. Only one wholly nonelectric force acts on the skier: the force of gravity.
A laser printer utilizes the forces between charged bodies. The
printer’s light-sensitive imaging drum is given a positive charge. As the drum rotates, a laser beam shines on selected areas of the drum, leaving those areas with a negative charge. Positively charged particles of toner adhere only to the areas of the drum “written” by the laser. When a piece of paper is placed in contact with the drum, the toner particles stick to the paper and form an image.
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