Science Around Us ! Part 2

33: What happens to a dry ice dropped into a tube of water?

Dry ice or solid carbon dioxide is one of relatively few substances that sublime-change directly into gas when it is heated, bypassing a liquid phase.

34: How do you jump?

Push your body up with your legs.

35: You can not drink through a straw that has a pin-hole near the top. Why?

The pin-hole does not allow you to remove air from the straw. Fresh air keeps coming in.

36: A snowflake is a tiny crystal of frozen water. What is its crystal symmetry?

Snowflakes of various shapes, but each has a six-fold rotational symmetry and a mirror- symmetry.

37: Why a kicked football would not continue on its path?

Kinetic energy is passed from the foot to the ball by applying a force to make the ball move. The momentum of the ball is affected by air resistance. The ball is pulled back down by gravity to the ground.

38: What image you get from a concave spoon?

A spoon causes light from a distant object such as are you to converge together as an inverted real image. You can see the real image hovering in front of the spoon or you can project it on to a small piece of paper.

39: When you overtake and pass a truck on the highway your car is drawn toward the truck. Why?

The air speeds up in the narrow channel between vehicles and its pressure drops. Surrounding air pushes the vehicles together.

40: Explain why a parachute slows your descent when you leap out of an airplane.

The air flow around the parachute is turbulent it increases pressure drag and reduces your terminal velocity. 

41: How do temperature changes cause the creaks and pops that you hear in your house at night?

As the house's different materials warm or cool, they expand or contract differently and slide past one another causing noises.

42: Is the violin string vibrating up and down, an example of standing wave or traveling wave?

Crests and troughs do not travel along the string. Instead the centre of the string becomes alternately a crest and a trough.

43: A household battery has positive and negative charge at its terminals. If you spin the battery very quickly at its centre of mass, will it become magnetic?

Yes, it will be magnetic.

44: As the Moon orbits the Earth, which way is the Moon accelerating?

Directly inward the Earth.

45: Why are jewels used in the watches?

Because its reduced friction and increase accuracy. The axle turns remarkably freely.

46: When you lift the lid of a hot vessel, its bottom surface is covered with water droplets. Why?

The water droplets are formed when water vapour in the hot, moist air above the vessel's water condenses on the cooler lid.

47: What happens to a spinning dancer when she pulls her arms in?

When she pulls her arms in, she reduces her moment of inertia. She begins to spin more rapidly so as to maintain the angular momentum.

48: Why a blackened baking pan is heated up more quickly in an oven than one that is shiny?

The blackened pan absorbs thermal radiation from the oven while the shiny pan reflects that thermal radiation.

49: How colds and influenza are spread?

When you sneeze, a cloud of tiny water droplets is ejected violently through the mouth and nose, carrying with it any microbes present in your lungs.

50: The topspin strokes in tennis appear to dive the ball downward. How?

A ball with topspin fall faster than it would without a spin. Topspin on a shot imparts a downward force that causes the ball to drop, due to its interaction with the air , so that ball accelerates downward faster than it would be by gravity alone. It travels very fast and remains inside.

51: How do firecrackers explode?

A firecracker suddenly releases the high pressure gas it contains producing the sound we hear. The firecracker creates the high pressure gas very abruptly using a chemical reaction. The higher the gas pressure, the more the shell tears and the louder the explosion.

52: Why the water rises up in the narrow, open ended capillary tube as it is placed in water?

Capillary action is the result of adhesion between water and glass combined with surface tension at the top of the water column. The surface forms a downward curve called meniscus.

53: While you apply the brakes on your bicycle, which way do you accelerate?

Backward, in the direction of your opposite forward velocity.

54: Ice boxes use melting ice to chill food. Why then the blocks of ice placed above the food compartment?

Chilled air near the ice is denser and sinks downward.

55: How the satellite dishes receive the transmission?

To receive the microwaves from a communication satellite on to its antenna, a satellite dish must be pointed directly at that satellite.

56: What is the purpose of crank in the automobile engine?

Crank is device that changes to-and-fro (reciprocal) motion to circular (rotary) motion or vice versa. A piston engine uses a crank to produce rotary motion.

57: Is light emitted by a fluorescent lamp coherent or incoherent?

It is incoherent.

58: What happens to sunlight falling on a black ball, a red ball and a white ball?

Black ball absorbs all the light, red ball aslo absorbs all colours of light but its not absorbs red light, and the white ball reflects all the light and absorbs nothing.

59: What is Cosmic ray?

A particle that comes from space. Cosmic rays are not rays, but fast-moving protons, electrons and nuclei.

60: Why can not you open a door by pushing on its hinged side?

A force exerted at the hinges produces no torque about them.

61: You can clean dust off a shelf by blowing on it hard. How does this work?

High speed air exerts enough drag force on dust to remove it.

62: How do gliders keep going without engines?

It is not only aero-foils that provide lift. Gliders also rely on thermals or currents of warm air to keep going without engines.

63: Why a normal audio tape represents sound in analogue form like a phonograph record?

The tape's magnetization is proportional to the change in air pressure that the tape is representing.