Identify the arrows that show input force

Figure 1: Downward arrow

Figure 2: Downward arrow

Figure 3: Upward arrow on the rod.

Explanation:

The initial force which is applied for a machine to begin work is known as an input force. Machines are designed such that input force increases so that output force increases. Mechanical advantage determines the quality of machine. It is the ratio of output force to the input force.

In figure 1, input force is applied in downward direction so the lever lifts up the barrel at the other end.

In figure 2, input force is applied downwards so that rope is pulled down and at the other end, the load is lifted upwards.

In figure 3, Input force lifts is applied in upward direction to lift the rod which drives the wheel.

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

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.