Why does object look larger in water relative to air?

In physics, refraction is normally the change in the path of a wave moving from one medium to a different or from a progressive change in the medium. Refraction of light may be the most commonly observed trend, but other waves for example sound waves and water waves also experience refraction. Just how much the wave is generally refracted is dependent upon the actual shift in wave speed and also the preliminary path associated with wave propagation relative to the path associated with alter in speed.

Light refraction follows Snell's law, which says that, for a given set of media, the ratio of the sines of the angle of incidence θ1 as well as angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in both media, or, the ratio of the indices of refraction (n2 / n1) of the two media. The refractive index or index of refraction of the material is a dimensionless quantity in optics that describes how fast light propagates within the material. The index of refraction indicates just how much the path of light is bent, or refracted, whenever entering a material.

Since air possesses a refractive index of essentially 1 and water comes with an index of refraction of just 1.33 the angle that the rays of light reach your eyes is bigger than the angle they might in air. This causes the angular size much larger for your eyes which makes the item appears larger compared to that they would likely appear in the air.

What is Nanotechnology?

Nanoscience and nanotechnology are the review and use of extremely small things and can be used across other science fields, such as chemistry, biology, physics, materials science, and engineering. Nanotechnology is taken as the scale range 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. One nanometer (nm) is one billionth, or 10−9, of a meter. Nanotechnology is the adjustment and production of materials and devices on the scale of atoms or small groups of atoms. Nanotechnology makes it possible to manufacture lighter, more robust, and programmable materials that require less energy to produce than conventional materials, that produce less waste than with conventional manufacturing, and that promise greater fuel efficiency in land transportation, ships, aircraft, and space vehicles. Nanotechnology may be able to make current medical applications less expensive and a lot easier to use in places like the general practitioner's office and at home. Researchers at the University of Toronto have demonstrated the use of nanoparticles designed to concentrate on a tumor and generate oxygen can increase the efficiency of the chemotherapy drug doxorubicin. Researchers have successfully used DNA origami-based nanobots capable of carrying out logic functions to achieve specific drug delivery in cockroaches. Cars are being manufactured with nanomaterials so they may need fewer metals and less fuel to function in the future. Scientists are now turning to nanotechnology in an attempt to develop diesel engines with cleaner exhaust gases. Nanotechnology also has a prominent role in the fast developing field of Tissue Engineering. Scientists currently debate the future implications of nanotechnology. Nanotechnology may be able to develop many new materials and devices with a vast range of applications, such as in nanomedicine, nanoelectronics, biomaterials energy production, and consumer products. On the other hand, nanotechnology raises many of the same issues as any new technology, including issues about the toxicity and environmental effect of nanomaterials and their potential issues on global economics, as well as questions about various doomsday scenarios. These concerns have led to a controversy among advocacy groups and governments on whether special rules of nanotechnology is called for.

Cool air from small opening and hot air from wide-open mouth

If you blow on your hand with your mouth open, your breath will be warm and if you do it with reducing the opening of your lips, your breath will be appreciably cooler. This is because expanding air is always cool and compressed air is always warm. A molecule picks up speed when it is hit by another molecule that approaches with a greater speed. But when a molecule collides with one that is receding, its rebound speed is reduced. The same idea applies to a region of air that is expanding: Molecules collide, on average, with more molecules that are receding than with molecules that are approaching. Therefore, in case of expanding air the speed of molecules decreases and thus cools the air. But in case of compressed condition, the molecule collide with more molecules that are approaching than with molecules that is receding. So, in case of compressed air the speed of molecules increases and thus warms the air.      

How do fishes survive in the coldest of winter?

When ice water freezes to become solid ice, its volume increases and its density is lowered. That’s why ice floats on water. If water were most dense at 0°C, it would settle to the bottom of a pond or lake. Water at 0°C, however, is less dense and floats at the surface. The water of a pond or lake freezes from the surface to the downward direction. The temperature at the bottom of an ice covered pond is 4°C, which is very much warm for the fishes that live there. More importantly, it is not possible to cover very deep ponds with ice even in the coldest of winters. This is because all the water must be cooled to 4°C before lower temperatures can be reached. For deep water, the winter is not long enough to reduce an entire pond to 4°C. This is because water has a very high specific heat capacity and poor ability to conduct heat. That is why the temperature in a cold region remains at a constant 4°C year-round.           

Why does water take longer times to warm than sand?

Specific heat capacity plays an important role here. It is defined as the amount of heat needed to change the temperature of a unit mass of the substance by 1 °C. It is also known as thermal Inertia which means the resistance of a substance to any change in its temperature. A relatively small amount of water absorbs a large quantity of heat for a correspondingly small temperature rise as water has a very high capacity for storing energy. Water also takes a long time to cool as it has a tendency to resist changes in temperature. For its higher heat capacity, it takes longer time to warm in presence of hot sunlight and longer time to cool on a cold night. Sands heat capacity is very low. Therefore, it warms quickly in presence of sunlight and cools quickly at night.   

Reason of dropping a coin straight into the glass by removing a card suddenly?

According to Newton's law of motion, If no external force is applied on a body, a stationary body will remain stationary and a moving body will continue to move without changing its speed. So a body continues to do whatever it happens to be doing unless a force is exerted upon it. In the absence of net forces, a moving body tends to move along a straight-line path indefinitely. It is the property of the body to resist changes in motion that is widely known as inertia. To show the property of that body experimentally, a card is put on the top of a glass with a coin on the upper face of the card. Now If we accelerate the card with a force, the coin will drop straight into the glass. As we said earlier, a stationary body continues to remain stationary due to inertia. As the coin was initially in stationary state, after removing the card very rapidly, it wanted to continue its state of rest. That is why it dropped straight into the glass.

How is it possible to lie without harm on a bed of nails?

We know that pressure is a force divided by area over which the force is exerted. When a person lies on a bed of nails, the force equal to the weight of that person acts on the surface of the bed containing nails. Here, the weight is distributed over hundreds of nails that makes the pressure at the tip of each nail safely small. If the same person stands on his feet, he will surely feel the sharpness of the nails because in this case the area of  contact is very small. So, the weight will be distributed over a few nails and hence the pressure will be relatively large.