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Subjects | Fact sheet | Samples
Science and technology: Sample images
ellipse
Technical terms used to describe an ellipse; for all points on the ellipse, the sum of the distances from the two foci, F1 and F2, is the same.
(Image © Helicon)
helicopter
The helicopter is controlled by varying the rotor pitch (the angle of the rotor blade as it moves through the air). For backwards flight, the blades in front of the machine have greater pitch than those behind the craft. This means that the front blades produce more lift and a backwards thrust. For forwards flight, the situation is reversed. In level flight, the blades have unchanging pitch.
(Image © Helicon)
Hohmann transfer orbit
A spacecraft in low Earth orbit (LEO) can change to a higher orbit in the same plane with minimum fuel expenditure by utilizing the Hohmann transfer orbit. Whilst in LEO the spacecraft fires its engines to increase velocity, causing the trajectory to become elliptic. This ellipse is carefully calculated to attain the desired final altitude. At this point the engines are again fired and the spacecraft transfers to the final orbit.
(Image © Helicon)
levers
Types of lever. Practical applications of the first-order lever include the crowbar, seesaw, and scissors. The wheelbarrow is a second-order lever; tweezers or tongs are third-order levers.
(Image © Helicon)
nerve cell
The structure of a nerve cell. The nerve impulse enters the nerve cell by the dendrites and is then carried away from the cell body by the axon.
(Image © Helicon)
polymerization
In polymerization, small molecules (monomers) join together to make large molecules (polymers). In the polymerization of ethene to polyethene (polythene), electrons are transferred from the carbon–carbon double bond of the ethene molecule, allowing the molecules to join together as a long chain of carbon–carbon single bonds.
(Image © Helicon)
stoma
The stomata, tiny openings in the epidermis of a plant, are surrounded by pairs of crescent-shaped cells, called guard cells. The guard cells open and close the stoma by changing shape.
(Image © Helicon)
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