What do we mean by the straightest possible path between two points on earth's surface?

The density of a substance is 4.0 g/cm3. if a sample of the substance has a volume of 25 cm3 then what is the mass

Holes drilled several kilometers into earth’s crust provide direct evidence about earth’s interior in the form of

The horizontal blue line through the middle of the lens is called the optical axis. as the lamp is moved above or below the axis, keeping the horizontal distance to the center of the lens constant, how does the horizontal distance from the lens to the image change?