Question Corner

QUESTION: Why do planes fly at very high altitudes between U.S. and Europe when there are no mountains in the way?

ANSWER: Drag on an aircraft is greatly reduced at altitude, so it can fly faster. In essence, that is because there are fewer air molecules to get in the way.

Engineers express the way altitude affects speed by calculating two speeds for an aircraft: the indicated air speed (IAS) nand the true air speed as (IAS). IAS is measured by air molecules entering a forward-facing, open-ended intake the air pressure this creates moves the speedometer needle.

At sea level, IAS equals TAS. If you fly higher, the air is less dense. So, to get the same number of molecules down the intake, you fly faster. Now TAS is no longer the same as IAS, and at cruising level TAS is about twice IAS.

Lift and drag both depend on IAS, not TAS. The higher you go with the same speed on your IAS speedometer, the faster you will actually go over the ground.

Engines for commercial airliners are also designed to operate better at altitude. Optimum fuel performance is achieved at about 80 to 90 per cent of the engine's maximum revolutions per minute (RPM). Air density decreases with altitude and, at fixed RPM, so does thrust.

Only at high altitude will the drag be low enough to allow maximum engine efficiency. To push the aircraft along at the same speed at a lower altitude, where the air is denser, the engines would have to operate at a lower percentage of maximum RPM.

While reduced drag is the primary reason for high- altitude flight, there are a other factors which benefit from flying at such levels.

- New Scientist

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QUESTION :Why do people not get cancer in the heart?

V. Priya, Chennai.

ANSWER : Cancer does occur in the heart, but very rarely. Tumours are classified as benign (non-cancerous) and malignant (cancerous). Malignant tumours are further classified as primary tumours (arising from an organ) and secondary tumours (spread from other organs by direct extension (or) by tumour particles carried through blood and/or lymphatic stream and get deposited in new organs.). Cardiac tumours can arise from the wall of the heart chambers and also from the heart muscle.

Analytical studies show that 72 per cent of heart tumours are benign and the remaining 28 per cent are malignant. Commonly occuring benign tumours of the heart are: myxoma (40.8 per cent), lipoma (14.1 per cent), fibroelastoma (13.2 per cent), Rhabdomyoma (11.3 per cent), fibroma (5.3 per cent), and heamangioma (4.7 per cent). Common malignant tumours are: angiosarcoma (31.2 per cent), Rhabdomyosarcoma (20.8 per cent), mesothelioma (15.2 per cent), fibrosarcoma (11.2 per cent) and lymphoma (5.6 per cent).

Secondary malignant tumours can spread through the blood stream to the heart from the kidneys, uterus, stomach, colon and lungs. Direct extension of the tumours from the lung to the heart can also occur.

After complete removal of the benign tumours under open heart surgery, the cure rate is almost 100 per cent, whereas the success rate is limited in malignant tumours depending upon further spread of this tumour to other vital organs.

S. Balasundaram, Coimbatore

This Weeks Questions

How do scientists create artificial gravity?

Albert Jose, Kerala

Why is coconut water considered as purest form of water?

M.Mohan Doss, Annamalai Nagar, T.N.

How is the temperature of the sun measured?

Prakash Kumar, Gulbarga, Karnataka

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