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.