When you lift a book from the ground to your desk, what kind of work do you do, negative or positive? by lifting the book what do you change? does it gain or lose energy? what kind of energy?

Work done by us is positive. This changes its location and it gains Potential energy.

Explanation:

Positive work is said when the force exerted on the object is in the same direction as that of the direction of its displacement.

Negative work is said to be done when the force exerted on the object is in the opposite direction as that of the direction of its displacement.

In this case, the force exerted on the book is in the upward direction and is in the same direction as that of its displacement. Hence, we are doing a positive work. Gravity is doing a negative work.

When we lift the book, we are changing its location from ground to the desk and in this process, the book is gaining energy. The energy gained by the object is gravitational potential energy.

Gravitational potential energy is the energy which is possessed by the virtue of the object's position of location.

Hence, work done by us is positive. This changes its location and it gains Potential energy.

the five characteristics of adolescence are biological growth and development, and undefined status, increased decision making, increased pressure and the search of self.

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle  

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.