Short Questions !

1: When you shine a beam of flash-light horizontally at a glass full of water, why does it bend?

Abeam of flash-light passes through the surface of a glass full of water and gets refracted downwards away from the surface. As it re-enters the air, it is refracted back to an angle nearer to the surface.

2: How do cockroaches group together?

Cockroaches group together when they release a scent beacon. A cockroach will find its way with the help of a scent emitted by the phenomena.

3: What energy is transformed from a moving hammer to the nail?

The kinetic energy of the moving hammer is transferred to the nail as it strikes the nail.

4: Why does the iron powder stick to the magnetic strip of an ID or Credit card?

It is attracted to the poles of the magnetic recording particles and forms a pattern of stripes.

5: What crystal shapes you find in salt and sugar?

The atoms in salt always arrange themselves forming a six-sided box and the atoms in sugar arrange themselves creating a rectangular crystal that is slanted at both ends.

6: What relationship is established between the clay at the centre and the rotation of a potter's-wheel?

Momentum- it depends on the product of the mass of the ball of clay at the centre and the rotational velocity of the potter's-wheel

7: How does an improperly balanced wheel behave when a mechanic balances the wheel?

It rotates about its centre of mass, not its geometric centre. It appears to wobble as it turns. The centre of mass needs to be located on the rotational axis.

8: How does your skin detect pressure?

The skin has many functions, including sensory reception. It has different receptor cells at varying depths to detect-touch, pressure, pain and changes in temperature.

9: When can a kite fly?

A kite can fly into the sky if the wind keeps on blowing with the same strength in the opposite direction. Also kites fly by using static air currents on the underside to give lift.

10: Whatbfor bimetallic strips used in thermostats?

Bimetallic strips respond to a change in temperature. It consists of iron and copper bonded firmly together. The strip bends when heated because the copper expands more than the iron, thereby it breaks the circuit.

11: Why cordless phone do not work when it is far from its base unit?

The powers emitted by the base unit and the handset are small so that their waves are relatively difficult to detect, when the cordless telephone is too far from its base unit.

12: How does the screw move forward in the wood?

The wood screw employs mechanical advantage to convert a modest torque on the screwdriver into an enormous forward force that drives the screw in to the wood, It forms a screw thread in the wood and the screw uses this screw thread to push itself into the wood.

13: Why cannot a black and white photographic negative be enlarged beyond a certain size without appearing grainy?

The film's image itself consists of black grains of Tarte silver.

14: When you jump from a high place, why do you need to bend your knees for landing?

Flexing your knees allows them to absorb your kinetic energy gradually as you land, with small forces exerted over long distance.

15: Why 100-watt filament in a bulb has twice the surface area of 50-watt filament?

The amount of thermal radiation emitted by a hot object is proportional to its surface area.

16: What makes a soap-bubble to be in equilibrium?

A soap bubble finds its equilibrium in the sphere whose inward surface tension exactly balances the outward push of the inside air.

17: What causes you to feel heat on your skin in front of a heat lamp?

A heat lamp emits large amounts of invisible infrared radiation which you can not see but feel.

18: Why a hammer-thrower in sports leans back when he swings the hammer?

As he swings the hammer, the hammer- thrower leans back tobkeep his centre of gravity above his feet.

19: Is radiation harmful?

Ultra-violet rays from the Sun can cause sunburn. Too many X-rays can damage the microscopic cells of living things. But in daily life, most forms of radiation are controlled in their amounts and strengths so as not to cause harm to living things.

20: Can you eat in zero gravity?

Gravity carries food and drink down your throat. You can eat in zero gravity because it is muscular contradictions of the gullet that actually transport food and drink to the stomach.

21: Why is concave mirror used for shaving?

The concave mirror with its curved surface makes the man's face closer.

22: Why the toy Tippe Top soon after its release inverts so that it spins on the stem?

The cause of the odd inversion of the toy Tippe Top is friction with the surface on which the hemisphere is turning.

23: Why do some birds fly in V-formations?

Birds such as geese migrate in V-formations. This saves energy for the whole flock. The leading bird cuts through the air creating a slip- stream, which exerts a pulling force on the bird behind it. This slip-stream carries right to the tail of the formation so that each bird gets help from the bird in front of it.

24: What type of side mirrors are used by car drivers?

Drivers use convex mirrors to see traffic coming up behind.

25: Why fire-wood burns better when it is raised above the bottom of a fire-place on a grate?

The grate permits convection to carry air upward to the wood.

26: What for wide-angle lens is used in camera?

A wide-angle lens has a short focal length. This gives it a wide field of view, so that a large part of a scene forms an image on the film.

27: What happens to the water heading for the drain in the tub?

As the gravity pulls the water together toward a common centre, the water spins. The spin takes on ever more speed as it contracts into ever smaller circles and gurgles down the drain.

28: Why sky-divers in free fall have arms and legs stretched?

Sky-divers outstretch arms and legs to increase the drag, which always acts in the opposite direction to the motion. At a certain speed the drag exactly balances the force of gravity and so it will not allow them to fall any faster.

29: What limits the speed at which a level curve can be negotiated without sliding off the road?

Static friction between the tires and the road accelerates the car inward around the curve. At excessive accelerations the car skids.

30: How do smoke particles rise upward?

The hot burned gas rises upward in the cooler air and exerts upward drag forces on the smoke particles and carries them along with it.

31: What holds things in place in space?

All the matter in the universe stars, planets, clouds of gases, tiny particles of dust are held together by four invisible forces - gravity, electromagnetism, strong and weak nuclear forces.

32: What gives cola drinks flavour?

Cola drinks contain phosphoric acid to give them flavour, But the acid combines with the sugar in the drink to rot our teeth.

33: When air passes through a door left-slightly ajar, the door shuts. Explain.

When the volume of air passing through the gap moves fast enough, the door will shut as the air flowing through the narrow gap suffers a sharp drop in pressure Bernoullis principle.