A practical joke or prank is a situation set up to produce what the perpetrator imagines to be a humorous physical outcome at the expense of the target. As the set-up or deception is revealed (too late) to the victim, practical jokes are distinct from slapstick or knockabout, where the goal is make physical events appear miscalculated, inept or accidental. The term practical refers to the fact that the joke consists of someone doing something (a 'practise'), rather than the common sense of the word ('useful or sensible').

Types of practical joke include:

false signalling, such a 'kick me' note stuck on someone's back, an 'automatic door' sign on a normal swinging door, or dropping an empty carton on someone's foot after pretending it is heavy;
surprise disruption, employing (for example) trip-wires, whoopee cushions, peanut butter on the inside of a car door-handle, or a three legged podium for a public speaker;
visual deception, such as water-filled balloons, plastic wrap on a toilet seat, 'apple-pie beds' which have had the springs removed, fake flowers in the lapel which squirt water, rubber fruit and guns which unfurl a flag saying 'bang';
fool's errands such as sending someone to buy striped paint or write-only CD blanks (see also: snipe hunt);
hoax stories or situations perpetrated on or by the media such as fabricated UFO landings and fake celebrity interviews involing rude or ludicrous questions (see also: culture jamming);
spontaneous impersonations, such as taking an order for takeaway food from someone who has actually dialled a wrong number;
verbal and typographical pranks, such as printing a block of text so that the first letters of every line spell out an irreverant message, or teaching someone a useful phrase in another language which is actually an insult.
Practical jokes are features of various kinds of holidays, such as April Fool's Day, Halloween, the Day of the Holy Innocents (in Spanish-speaking cultures), and the night before May Day in Germany. They also feature in various rites of passage, such as stag nights.

The Trapezium of Xenophanes was cited by Aristotle as a notable compendium of practical jokes, but only a few fragments of this work have
Balloons as decoration or entertainment

Party ballonsParty balloons are mostly made of natural latex tapped from rubber trees and can be filled with air, helium, water, or any other suitable liquid or gas. The rubber makes the volume adjustable.Filling with air is done with the mouth or with a pump.When rubber balloons are filled with helium so that they float (restrained by ribbons or strings) they can hold their shape for only a few hours. The enclosed air or helium escapes through small pores in the rubber. If helium is used the gas escapes quicker than in the case of air because the helium atoms are much smaller than the nitrogen and oxygen molecules in air.

Even a perfect rubber membrane eventually loses the gas to the outside, and its contents are contaminated by oxygen and nitrogen migrating inward from the outside. The gases in question actually dissolve in the rubber on one side and are released from solution on the other. The process by which a substance or solute migrates from a region of high concentration, through a barrier or membrane, to a region of lower concentration is called diffusion. The inside of balloons can be treated with a special gel (e.g. "Hi Float" brand) which coats the inside of the balloon to reduce the helium leakage, thus increasing float time. Latex rubber balloons are completely biodegradable, but cannot safely be released into the environment: they are a serious hazard to birds and wetland animals that confuse the balloons for food.

Beginning in the early 1990s, some more expensive (and longer-lasting) helium balloons have been made of thin, unstretchable, impermeable metallized nylon films. These balloons are often mistakenly called Mylar balloons. These balloons have attractive shiny reflective surfaces and are often printed with colour pictures and patterns. The most important attributes of metallized nylon for balloons are its light weight, increasing buoyancy and its ability to keep the helium gas from escaping for several weeks. However, there has been some environmental concern, since the metallized nylon does not biodegrade or shred as a rubber balloon does, and a helium balloon released into the atmosphere can travel a long way before finally bursting or deflating. Release of these types of balloons into the atmosphere is harmful to the environment.

Partygoers sometimes entertain each other by untying a balloon and inhaling the helium. Because the speed of sound in helium is about twice that in air, the helium causes the vocal tract to become more responsive to high-pitched sounds and less responsive to lower ones. The result is a voice that sounds high-pitched (and usually very funny).

Balloon artists are entertainers who twist and tie inflated tubular balloons into sculptures (see also balloon animal). The balloons used for balloon sculpture are made of extra-stretchy rubber so that they can be twisted and tied without bursting. Since the pressure required to inflate a balloon is inversely proportional to the diameter of the balloon, these tiny tubular balloons are extremely hard to inflate initially. A pump is usually used to inflate these balloons.
Decorators may use dozens of helium balloons to create balloon sculptures. Usually the round shape of the balloon restricts these to simple arches or walls, but on occasion more ambitious "sculptures" have been attempted with great success. The balloon decorating industry offers everything from simple balloon columns to stunning, very large and detailed sculptures.

Water balloons are thin, small rubber balloons intended to be easily broken. They are usually used by children, who throw them at each other, trying to get each other wet - see practical joke.

Balloons in medicine
Angioplasty is a surgical procedure in which very small balloons are inserted into blocked or partially blocked blood vessels near the heart. Once in place, the balloon can be inflated to clear or compress arterial plaque, and to stretch the walls of the vein. A small stent can be inserted in its place to keep the vessel open after the balloon's removal. See myocardial infarction.Certain catheters have balloons at their tip to keep them from slipping out, for example the balloon of a Foley catheter is insufflated when the catheter is inserted into the urinary bladder and secures its position.

Maximum flight heights
Manned Balloon

The altitude record for manned ballons is 34668 metres. It was made in 1961 by Malcolm D. Ross and Victor E. Prather over the Gulf of Mexico in 1961.

Unmanned Balloon

The altitude record for unmanned balloons is (1991 edition of Guinness Book) 51.8 kilometres. The vehicle was a Winzen-Balloon with a volume of 1.35 million cubic metres, which was launched in October 1972 in Chico, California, USA. This is the greatest altitude ever reached by a flying object requiring the surrounding air. Higher altitudes can only be reached by ballistic vehicles such as rockets, rocket planes or projectiles.