Wheels can slip, meaning they fail to get a grip, on loose or slippery ground. Slipping wastes energy, and can lead to loss of control or becoming unable to move. This happens to cars on mud, ice, and snow. Where wheels have this problem, people sometimes use other mechanisms instead. In the logging industry, vehicles with legs are sometimes used to reach areas that are more difficult than what wheels can deal with. Vehicles with tracks, like tanks, don't slip as much as vehicles with wheels, because they have a larger area touching the surface. However, vehicles with tracks often have a larger turning radius than wheeled vehicles, meaning they take more space to turn. They are also less efficient, and more complex to build.
The engineer Mieczysław G. Bekker showed that in natural terrain, small obstacles are much more common than large ones. This is called a "log-normal" distribution. This means that obstacles are a problem for wheeled vehicles of all sizes. The main ways of dealing with obstacles are to go around them, and to go over them.
The most common types of steering do not include separate articulation (joints for bending) for each wheel, so they have a limited turning radius. This limits how well these kinds of vehicles can move around where there are a large number of obstacles.
Michael LaBarbera of the University of Chicago shows the limited turning radius of wheels by comparing humans walking with humans in wheelchairs. Jared Diamond points out that most examples of rolling in nature are found in wide open, hard terrain. This includes the use of rolling by dung beetles and tumbleweeds.
Wheels are bad at dealing with vertical (upright) obstacles, especially obstacles about the same size as the wheel itself. If a vehicle or animal can move its center of mass, then the largest vertical obstacles that can be climbed are half as high as the wheel. If the center of mass cannot be moved, the highest obstacle that can be climbed is one eighth to one quarter the height of the wheel.
Also, without joints, a wheeled vehicle can become stuck (unable to move) on top of an obstacle, with the obstacle between the wheels so they don't touch the ground. Limbs, unlike wheels, are useful for climbing, and can deal with difficult terrain.
For wheels without joints, climbing obstacles will cause the body of the vehicle to tilt. If the weight of the vehicle moves outside of the wheels, the vehicle can tip over because of "static instability". At high speed, a vehicle's inertia can cause it to become "dynamically unstable". This means it can be tipped over by a smaller obstacle, or simply by turning or changing speed too quickly. Without jointed limbs, it can be impossible to recover from being tipped over.
Limbs used by animals to move over terrain are often also used for other purposes, such as holding and manipulating things, climbing, swinging from branches, swimming, digging, jumping, throwing, kicking, and grooming. Without joints, wheels are not as useful as limbs for these jobs.
The hoop snake is an animal described in legend in the United States and Australia. The snake is said to hold its tail in its mouth and roll like a wheel towards its victims. The Japanese Tsuchinoko is a similar legendary animal.
The 1944 science fiction short story "Arena", by Fredric Brown, includes a telepathic (mind-reading) alien called an "Outsider". The Outsider is shaped like a ball and moves by rolling. A 1967 "" episode with the same name was based on the story. A 1964 episode of "The Outer Limits" called "Fun and Games" may have been based on the same story. Neither television episode included a rolling animal.
The Dutch artist M. C. Escher invented an animal that he named "Pedalternorotandomovens centroculatus articulosus". This animal was able to roll itself forward like a wheel. Escher drew the animal in his 1951 picture (also known by the English title "Curl-up").
A 1956 Scrooge McDuck comic by Carl Barks, "Land Beneath the Ground!", included "Terries" and "Fermies", characters who move from place to place by rolling like a bowling ball. The Terries and Fermies have turned their rolling into a sport, causing earthquakes in the process.
"Tuf Voyaging", a 1986 science fiction novel by George R. R. Martin, includes a type of alien called a "Rolleram", which kills its victim by rolling over it.
In the "Sonic the Hedgehog" video game series, the main character Sonic and his sidekick Tails move by rolling. The "Sonic the Hedgehog" series first appeared in 1991.
The 1995 short story "Microbe", by Kenyon College biologist and feminist science fiction writer Joan Slonczewski, is about a trip to explore an alien world, where the plant and animal life is entirely made of doughnut-shaped organisms.
L. Frank Baum's 1907 children's book "Ozma of Oz" includes human-like creatures with wheels instead of hands and feet, called "Wheelers".
The 1968 novel "The Goblin Reservation" by Clifford D. Simak includes an intelligent kind of alien that uses natural wheels.
Piers Anthony's 1977 book "Cluster" and its sequels (the later books in the same series) include a type of aliens called Polarians. The Polarians move around by holding and balancing on a large ball. The ball is a living part of the Polarian's body that can be removed temporarily.
David Brin's "Uplift" Universe includes a kind of wheeled alien called the G'Kek. The G'Kek are described in the 1995 novel "Brightness Reef". In the 1996 novel "Infinity's Shore", the G'Kek are said to look like "a squid in a wheelchair." They suffer from arthritis in their axles as they become old, especially when living in an environment with high gravity.
A 1997 novel in the Animorphs series, "The Andalite Chronicles", includes a kind of aliens called Mortrons. The Mortrons are made of two separate living parts: a yellow and black bottom half with four wheels, and a long, red head with sharp teeth and hidden wings.
The 2000 novel "The Amber Spyglass", by English author Philip Pullman, includes a type of alien known as the Mulefa. The Mulefa have diamond-shaped (◊-shaped) bodies with one leg at the front and back and one leg on each side. The Mulefa use large, disc-shaped seed pods as wheels. They hold the pods on axles made of bone on their front and back legs, while pushing themselves with their side legs. The Mulefa and the seed pod trees have a symbiotic relationship, or a relationship that helps both sides: the Mulefa use the seed pods as wheels, and the seed pod trees depend on the rolling to crack open the pods and allow the seeds to spread.
In the 2000 novel "Wheelers", by English mathematician Ian Stewart and biologist Jack Cohen, a kind of alien called "blimps" can grow machines called "wheelers", which use wheels to move.
The 2009 Disney children's television series Jungle Junction includes jungle animals with wheels instead of legs. One of these animals, "Ellyvan", is a hybrid (a combination) of an elephant and a van. These animals move around their home on highways.
Idris Sardi
Idris Sardi (June 7, 1938 – April 28, 2014) was an Indonesian violinist. His career lasted for nearly 50 years until retiring in 2013 because of ill health. Sardi was born to Mas Sardi, an Indonesian composer, and Hadidjah, an Indonesian actress.
Sardi died at Meilia Hospital in Cibubur, Indonesia from an illness. He was 75 years old.
Cordial (candy)
A cordial is a kind of candy in which a fruit filling is placed within a chocolate shell. A common candy of this kind is the cherry cordial.
June Angela
June Angela (born June Angela Profanato, August 1959) is an American actress, tap dancer and singer. She was 10 years old in season 1 (1969-1970) of "Sesame Street" (where she cameo appeared) and 12-17 and 49 years old in seasons 1-7 (1971-1977, 2006 and 2009) of "The Electric Company".
2011 Tuscaloosa–Birmingham tornado