1. If you're in the US, it's going to cost money to switch: stores will have to chuck their old weighs and measurements and purchase new; truck scales will have to change their systems, fuel stations.... the impact to industry is non-trivial and that costs moolah.
2. Metric units may not be convenient, as we think of them, for everyday use. Imagine ordering a pint of beer - "I'll have 568ml!" you might call in the UK, whereas when ordering from a barkeep in the US of A, you'd call for a cool 473ml. Unless you're drinking an IPA, in which case it wouldn't be that cool. But it's okay, it's meant to be consumed that way. In my opinion, we'd likely still keep the colloquial reference, and not care too much.

 Air filled cavities are found in aquatic plants in their body which makes them spongy and buoyant so that they can float on the surface of water.

The path along which electricity can flow is called an electric circuit. A simple electric circuit can be made by using a cell, a torch bulb and two pieces of wire.

A torch bulb is connected to the positive and negative terminal of the cell by using two pieces of wires called connecting wires. On connecting the torch bulb between the two terminals of a cell, the bulb lights up or glow because electricity flows through its filament.

The wires and the bulb form a continuous path between the two terminals of the cell. This path is called electric circuit. The bulb glows when electricity passes through the circuit.

Fishes have the shallow streamlined body so they can swim easily. They have slippery scales on their bodies that protect the fish and also help in easy movement through water.

The dust particles which remain suspended in air get loaded and come down on the ground due to rainfall, this is the reason that the sky and the air look clean and clear after rainfall.

If the carbon-dioxide percentage increases it will cause a greenhouse effect, i.e. the carbon dioxide present in our atmosphere will not allow the hot rays of sun to escape back into space from the atmosphere after reflection. Once they enter the earth’s atmosphere, they increase the overall temperature of the earth, which will also cause the ice on mountains to melt, and subsequently water level will rise.

In general compounds are formed by the chemical combination (chemical reaction) of different elements, molecules with each other. Whereas mixtures are formed by the combination of different elements, molecules and even compounds which are not chemically reacted with each other.
Air is considered as a mixture of gases, as the component gases does not reacts with each other.
If the gases present in it reacts with each other then it will not considered as mixture but as a compound.

Carbon dioxide is required by green plants to make their food by the process of photosynthesis. All plants and animals consume oxygen for respiration and produces carbon dioxide.

Earthworms breathe through their skins. The skin of an earthworm feels moist and slimy on touching. The skin of earthworm has a good blood supply. So, the earthworm absorbs the oxygen needed for respiration through its thin and moist skin. Gases can easily pass through them

The density of the blanket of air that surrounds us becomes thinner as we go up. 

Freezers are always on top of a fridge due to the nature of convection. The natural law of convection is that warm air rises while cold air falls, so the freezer at the top provides cold air for the other compartments at the bottom of the freezer.

Measurement: Comparing an unknown quantity with some known quantity is called measurement.

Result of Measurement: The result of measurement has two parts; one part is the number and another part is the unit. The known quantity which is used in measurement is called a unit. For example; when you say that your height is 150 cm then the measurement of your height is being expressed in a number, i.e. 150 and a unit, i.e. centimeter.

Arbitrary Units of Measurement: Before the development of standard units of measurement, people used arbitrary units of measurement. Some of them are still in use at some places. Handspan, finger-length, cubit (length between the elbow and finger tips), foot-length and arms-length are some examples of arbitrary units of measurement.

The process of sending back the rays of light which falls on the surface of an object is called reflection of light. The objects having polished shinning surfaces reflect more light than objects having unpolished dull surfaces. Like shinning silvered mirror reflects back almost all the light which falls on it. The smooth surface of the still water could also act as a mirror so that we can see the images of trees and other objects in a lake.