Science Around Us ! Part 4

86: What is the ‘mind's eye"?

It is the place where we can imagine scenes and views that our eyes might see-even with our eyes closed.

87: In everyday language people tend to confuse the terms 'mass' and 'weight'. Explain.

Both words seem to refer to how heavy something is in everyday language. An object's mass is the amount of stuff it contains, while its weight is the force of gravity on that object.

88: A pearl dropped into a jar of honey descends much more slowly. Explain.

The pearl experiences more viscous drag in the viscous honey.

89: If you blow carefully across the top of a bottle you can get it to whistle. When it is half full of water it will whistle with increased pitch. Why?

The shorter air column is stiffer and its mass is smaller.

90: How do a submarine crew see the view above the surface?

A periscope allows the crew to look the surface, which contains two mirrors reflecting a light beam twice

91: It is possible to run quickly through a bed of hot coal without burning your feet. The secret is to have water or sweat on your feet. Why?

The moisture evaporates rapidly as its temperature rises, a phase transition that requires enormous amounts of heat.

92: Why are cars designed with their heavy engines nearer to the ground?

It is to keep their centre of gravity low.

93: What sounds do elephants perceive?

Elephants perceive infra-sounds which have very low frequencies that are inaudible to humans.

94: How many images of yours is seen when you stand in between two parallel mirrors?

A pair of parallel mirrors produces infinity images.

95: What makes rockets the best engines for space?

A rocket needs no air unlike jet engine. Most rocket engines get their thrust from the reaction between a fuel, such as liquid hydrogen and an oxidant (liquid oxygen), which allows the fuel to burn.

96: The plastic cup covers provided by fast food restaurants often have buttons. When you push the button, you bend the glassy plastic and it turns white Why?

The plastic crazes when it is bent forming gaps that scatter light.

97: How is torsion produced in a bar?

Torsion occurs in a bar when one end is fixed and the other end is turned.

98: Speed bumps are ridges that are put into streets to keep cars from driving too fast. How does it affect fast moving cars?

A fast moving car must accelerate upward much faster to acquire the upward speed it needs to move over the bump quickly.

99: Why does squinting your eye increase your depth of focus and make it easier to focus?

Reducing the size of your eye's lens increases its depth of focus.

100: What is magnifying glass?

A magnifying glass is a converging lens and can form a real image. It brings light spreading outward from the room lights together onto the sheet of paper as a real image.

101: When you serve a volley-ball it flies over the net and dithers slightly from side to side. What causes this?

Small disturbances in the airflow around the sides of the non-spinning volley-ball produce lift forces that push the ball to the side.

102: The wheel of fortune game uses a large spinning disc with nails projecting from the wheel's outer edge. How does the flexible strip that pushes against nails stop?

The strip exerts its force far from the wheel's pivot and thus produces a substantial torque on the wheel to slow its rotation.

103: How does an arrow's heavy head help the arrow remain stable in flight?

The massive head shifts the arrow's centre of mass forward so that centre of pressure is well behind its centre of mass.

104: If you lean left as you turn left while running why do not you fall over the left?

The leftward frictional force on your feet keeps you balance.

105: Why the adhesive on the back of a postage stamp is polymer?

It softens when you lick it and hardens when it dries out. Water plasticizes the adhesive temporarily softening it.

106: What happens when object moves or drops?

When an object moves or drops it bumps into the small particles or molecules that surround it. The travelling molecules bump into your ear drum which begins to vibrate. Your nerve endings carry these vibrations to your brain which translates them into sound.

107: One of the delightful aspects of a diamond is its strong dispersion. Explain.

A diamond exhibits dispersion and bends violet light much more than red light so that sunlight is separated into its different colours as it passes through the stone

108: How does a fish detect pressure?

A fish has a lateral line of hair cells on its body, which helps to detect water pressure and to navigate while swimming.

109: Why does air become hot when you pump it into a bicycle tire with a hand pump?

You do work on the air and the air's thermal energy increases.

110: How does a flute produce a note?

As air is pumped through the flute at the bottom of the pipe, it hits the upper lip and produces an audible frequency, which is amplified in resonance with the length of the pipe.

111: What happens when you expose magnetic strip of your ID card or credit card to a strong magnetic field?

It magnetizes the recording particles in a direction and makes it unreadable.

112: How small is small?

Small objects can be seen with ordinary microscope, but the nanoworld is so small it must be magnified many tens of thousands of times to be visible.

113: How can a bird bring down a jet plane?

The greatest danger is that a large bird or a flock of small ones, like starlings, might be sucked into the air intake of the jet engine causing it to stop.

114: The snow sublimes to form water vapour in the air. Explain.

Ice sublimes quickly at temperatures near its melting temperature, going from a solid to a gas without ever becoming liquid water.

115: Where do you find mirrors with hyperbolic cross-section?

Hyperbolic mirrors are found in some reflecting telescopes and special purpose cameras and behind the light sources of flash-lights and torch-lights.

116: Why is smoking harmful?

Cigarette smoke contains substances, which are all deposited straight into the many harmful lungs. The smoke contains tiny particles of soot that can clog the air passage. The nicotine in cigarette can affect the heart and circulation.

117: Why the rider of the Rotor in an amusement park stick to the rotor wall when the Rotor speed reaches the maximum?

From his perspective a centrifugal force pins him there. The resulting friction between him and the wall prevents him from falling.

118: How do you increase the angular momentum, when you spin a toy-top with your finger?

You are exerting a torque on it for a time- an angular momentum.

119: Museums often display priceless antique manuscripts under dim yellow light. Why not white light?

Photons in ultraviolet or blue light can cause chemical damage to the molecules in the manuscripts. Yellow light generally cannot.

120: Why are Sodium vapour lamps used as street lights?

Yellow light from Sodium vapour lamps pass through fog better than white light.

121: If two golf balls one with dimples and the other with smooth surface are dropped simultaneously from a tall tower, which will hit the ground first?

The dimpled golf ball will hit the ground first as it reduces pressure drag.

122: Pure Gold (24 carat) is generally too soft for jewellery. Alloys such as 18 carat and 22 carat are much harder. Why?

By disrupting gold's crystal structure, alloying elements make it less able to undergo slip and make it harder than pure gold.