25

In 1896 the French physicist Henri Becquerel noticed that pitchblende had one very unusual property: photographic plates exposed to a sample of pitchblende reacted as if they had been exposed to light. This property was called radioactivity, but at the time many scientists dismissed it as being of little importance. However, the investigation of what caused the radioactivity was to lead to one of the most significant discoveries in science, a discovery that laid the foundations for modern nuclear physics.

22

An odd device patented in Britain in 1904 by a Prussian count, Vladimir Skorzewski, was a compressed air walking assister. It consisted of a seat and handlebars, shock absorbers, and leg extensions and soles attached to stirrups. The count’s notion was that the shock absorbers at the contraption’s joints would function much like a series of miniature pogo sticks. The user could bound along the street and still enjoy the comforts of sitting down while “walking”.

28

According to the Principle of Conservation of Momentum, the expulsion of hot gases through the rear of rockets or air crafts will produce a large momentum in the opposite direction. The forward thrust of a jet engine enables the aircraft to move forward while the upthrust of a rocket engine enables the rocket to propel upwards..

26

As the plane cuts through the air, the air that flows over the top of its wings has to travel a greater distance than the air flowing underneath its wings. So the air has to travel faster over the top than the bottom. Hence the air pressure on the top and bottom of the wings produces an upward force or lift that pushes the wings upwards.

33

The smooth sides and rounded outline of the shape do not disturb the flow of water and do not cause turbulence behind the object. Turbulence causes drag in a vehicle. The hulls of vehicles that are immersed in water are streamlined so that the vehicles can sail faster through the water. The center of gravity of the vehicles in water must be below the water level so that the vehicle is stable and balanced when moving on water..

21

In the respiratory organ, blood receives oxygen, and then transports it to all the living parts of the body where it is used in tissue respiration..To function efficiently, a respiratory organ has a large surface area for rapid oxygen uptake and a very good supply of blood in a dense network of blood capillaries, which are separated from the surrounding air or water by an epithelium made up of a very thin layer of cells..

18

Greenhouse gases are trapped and build up in the atmosphere near the earth’s surface. This makes the earth warmer than normal. The warning effect of the trapped greenhouse gases causes changes in the weather patterns on a global scale. Rainfall pattern changes, sea level rises and droughts prevail.

22

The scientific investigation method is important as it provides a systematic and complete way to acquire scientific knowledge. It also teaches us to think critically and analytically..Science discoveries help us to understand and appreciate our environment and improve the quality of life.

23

..This maintenance of a constant internal environment is called homeostasis. Homeostasis ensures that the body cells are provided with a relatively constant environment so that they work efficiently and optimally, even though there might be changes outside the body..

29

Endocrine glands are also known as ductless glands. They secrete hormones directly into the bloodstream. The endocrine glands I in both males and females are the same except for the testis (male) and the ovary (female). The majority of endocrine glands are controlled by the pituitary gland but some are stimulated by the nervous system or by chemical substances.