Category Science

WHAT ARE SIMPLE MACHINES?

Levers, wedges, slopes, screws, wheels, gears and pulleys are all known as simple machines. They make work easier by enabling a small force to move a large load. Machines may magnify (increase) a force or a movement.

A simple machine is a mechanical device that changes the direction or magnitude of a force. In general, they can be defined as the simplest mechanisms that use mechanical advantage (also called leverage) to multiply force. Usually the term refers to the six classical simple machines that were defined by Renaissance scientists: Lever, Wheel and axle, pulley, Inclined plane, Wedge and Screw.

A simple machine uses a single applied force to do work against a single load force. Ignoring friction losses, the work done on the load is equal to the work done by the applied force. The machine can increase the amount of the output force, at the cost of a proportional decrease in the distance moved by the load. The ratio of the output to the applied force is called the mechanical advantage.

Simple machines can be regarded as the elementary “building blocks” of which all more complicated machines (sometimes called “compound machines”) are composed. For example, wheels, levers, and pulleys are all used in the mechanism of a bicycle. The mechanical advantage of a compound machine is just the product of the mechanical advantages of the simple machines of which it is composed.

Although they continue to be of great importance in mechanics and applied science, modern mechanics has moved beyond the view of the simple machines as the ultimate building blocks of which all machines are composed, which arose in the Renaissance as a neoclassical amplification of ancient Greek texts. The great variety and sophistication of modern machine linkages, which arose during the Industrial Revolution, is inadequately described by these six simple categories. Various post-Renaissance authors have compiled expanded lists of “simple machines”, often using terms like basic machines, compound machines, or machine elements to distinguish them from the classical simple machines above. By the late 1800s, Franz Reuleaux had identified hundreds of machine elements, calling them simple machines. Modern machine theory analyzes machines as kinematic chains composed of elementary linkages called kinematic pairs.

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IN SCIENTIFIC TERMS, WHAT IS WORK?

To a scientist, work is done when a force causes something to move. The unit of measurement used for work is the joule. A joule of work is done when a force of one newton moves something one metre (3.3 feet). The force needed to lift a small apple is about one newton.

On a typical day, you probably wake up, get dressed, eat breakfast, and head off to work. After you spend all day at your job, you go home, eat dinner, walk the dog, maybe watch some TV, and then go to bed. In this sense, work can be just about anything – construction, typing on a keyboard, driving a bus, teaching a class, cooking food, treating patients, and so much more.

But in physics, work is more specific. This is the displacement of an object due to force. How much work is done depends on the distance the object is moved. This makes it easy to put work into a solvable equation: work = force * distance. While this equation is fairly straightforward, there are three important things to note. First, the object must move over some distance in order for work to be done. Second, the force and the distance of movement must be in the same direction. And finally, the force must be constant.

The units we use for work are joules (J), named for James Prescott Joule. Though he is now known for his work in science, he actually preferred brewing beer… until he realized how science could help him be a better brewer!

The joule is a combination of both of the components on the right side of our work equation: force and distance. Quite simply, a joule is a Newton-meter (N*m), and one joule of work is done when a force of 1 N is exerted over a distance of 1 m.

This amount of work is on par with lifting an apple over your head. I bet you didn’t realize that counted as work, but in the world of physics, it does! You can probably see that 1 J isn’t really practical to use for larger amounts of work, so instead we use kilojoule (kJ), which is 1000 J, or megajoule (MJ), which is 1,000,000 J.

Regardless of the amount of work done, it involves three key components: the amount of force, the distance displaced, and the cause of the displacement, which is the force itself.

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ARE HUMAN BEINGS THE ONLY ANIMALS TO USE TOOLS?

The simplest tools often act as extensions of parts of the body. For example, if your arms are too short to reach a ball that has fallen into a pond, you may use a stick to lengthen your reach. The stick is a tool. Many non-human animals use simple tools: chimpanzees use sticks to scoop ants from their mounds; thrushes drop snails’ shells onto a flat stone or “anvil” to crush them; some vultures drop stones onto other birds’ eggs to break the shells. Tools, used by humans or other animals, help to make work easier to do.

Scientists once thought of tool use as a defining feature of humans, but increasingly research is showing adept tool users on land, air and sea in the animal kingdom. Investigating how such behavior developed in this diverse mix promises to shed light on how tool use might have originated in humanity.

Chimpanzees

Chimpanzees are humanity’s closest living relatives, and apparently learned how to make and use tools long ago without human help, with stone hammers found at a chimp settlement in the Ivory Coast dating back 4,300 years. They are even capable of making spears to hunt other primates for meat, and are known to have developed specialized tool kits for foraging army ants.

Crows

Increasingly, scientists find that crows and their relatives have exceptional birdbrains, proving extraordinarily adept at crafting twigs, leaves and even their own feathers into tools. Researchers have even discovered that crows might learn to drop stones in pitchers to raise the height of water inside, just like in Aesop’s fable.

Orangutans

Orangutans in the wild have developed and passed along a way to make improvised whistles from bundles of leaves, which they use to help ward off predators. This apparently marks the first time an animal has been known to use a tool to help it communicate, and is mounting evidence that culture — defined as knowledge passed from one generation to the next — isn’t something unique to us humans.

Elephants

Elephants are among the most intelligent animals in the world, with brains larger than those of any other land animal. Anecdotes suggest they can intentionally drop logs or rocks on electric fences to short them out and plug up water holes with balls of chewed bark to keep other animals from drinking them away. Asian elephants are even known to systematically modify branches to swat at flies, breaking them down to ideal lengths for attacking the insects.

Gorillas

Gorillas aren’t just extraordinarily strong — roughly 10 times stronger than a full-grown man — but they possess brains as well. Wild gorillas are known to use branches as walking sticks to test water depth and trunks from shrubs as makeshift bridges to cross deep patches of swamp. While other great apes mostly use tools to help get at food, gorillas apparently use them to help them deal with their surroundings in other ways.

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HOW DO FIREFIGHTERS PROTECT THEMSELVES FROM HEAT?

Firefighters need to wear clothing that is both fire retardant (slow to catch on fire) and offers good insulation (does not conduct heat easily). Fireproof clothing often has a shiny surface, because this helps to reflect the radiated heat away from the body.

It’s the outside of the suit that is bright and shiny.  That’s because things that are lighter in color and more reflective will reflect more energy away from them than they will absorb.  The inside of the suit is made of a fireproof type of material designed to further insulate the firefighter from experiencing the heat transfer from the fire he is trying to put out.  Fabrics that traditionally are poor conductors of heat have been used, like asbestos.  Asbestos fibers have also proven to be carcinogenic (cancer causing), so newer fabrics are constructed out of non-carcinogenic materials, such as newer fire retardant materials.  Firefighters that combat wildfires in the American mid-west have, as part of their safety equipment, a shiny, flame-retardant tent they take shelter in, if the fire reverses direction and overtake them.  They may cover up in these fireproof tents in an effort to preserve their lives.

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HOW DOES A THERMOMETER WORK?

As substances get hotter, their molecules move around more rapidly and they may take up more space. A thermometer contains a liquid that expands as it gains heat energy. This causes the level of the liquid to rise in a narrow tube. A scale beside the tube allows the temperature to be read.

The simplest thermometers really are simple! They’re just very thin glass tubes filled with a small amount of silvery liquid (typically mercury—a rather special metal that’s a liquid at ordinary, everyday temperatures). When mercury gets hotter, it expands (increases in size) by an amount that’s directly related to the temperature. So if the temperature increases by 20 degrees, the mercury expands and moves up the scale by twice as much as if the temperature increase is only 10 degrees. All we have to do is mark a scale on the glass and we can easily figure out the temperature.

How do we figure out the scale? Making a Celsius (centigrade) thermometer is easy, because it’s based on the temperatures of ice and boiling water. These are called the two fixed points. We know ice has a temperature close to 0°C while water boils at 100°C. If we dip our thermometer in some ice, we can observe where the mercury level comes to and mark the lowest point on our scale, which will be roughly 0°C. Similarly, if we dip the thermometer in boiling water, we can wait for the mercury to rise up and then make a mark equivalent to 100°C. All we have to do then is divide the scale between these two fixed points into 100 equal steps (“centigrade” means 100 divisions) and, hey presto, we have a working thermometer!

Not all liquid thermometers use mercury. If the line you see in your thermometer is red instead of silver, your thermometer is filled with an alcohol-based liquid (such as ethanol). What’s the difference? Mercury is toxic, although perfectly safe if it’s sealed inside a thermometer. However, if the glass tube of a mercury thermometer happens to break, that potentially exposes you to the poisonous liquid inside it. Alcohol thermometers are generally safer for that reason and they can also be used to measure lower temperatures (because alcohol has a lower freezing point than mercury; it’s about ?114°C or ?170°F for pure ethanol compared to about ?40°C or ?40°F for mercury).

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HOW IS HEAT ENERGY MEASURED?

Heat energy, like other forms of energy, is measured in joules (J). Temperature is measured in degrees Fahrenheit (°F), Celsius (°C) or Kelvin (K). In Fahrenheit, water freezes at 32° and boils at 212°. The Celsius scale is based on the boiling and freezing points of water, so these are 100°C and 0°C respectively. Kelvin units are the same as Celsius degrees but they start from the lowest temperature possible. On this scale, water freezes at 273K.

We have all felt various levels of heat. Our skin is a good detector of heat and we interpret the average molecular motion within an object as a feeling that the object is hot or cold. However our skin does not always give us consistent measurements of heat energy.

For this we need special instruments which can accurately measure temperature, like a thermometer. Thermometers, and other temperature measuring devices, are used to get a quantitative measure of the average motion of the molecules in a substance. They interpret this average molecular motion as a certain number of degrees which we call the temperature.

We have all used thermometers to measure the level of heat but sometimes we need to measure heat in places where you can’t put a thermometer. For example, in space, in molten metals and in hot fires. To make measurements in these situations we need instruments which can measure heat without touching the heat source. These instruments measure the heat radiation emitted by the heat source. Examples of these types of devices are infrared cameras and detectors.

Heat is measured in quantities called joules (pronounced the same as jewels) in the metric system and in British Thermal Units (BTU) in the English system. Heat can also be measured in calories.

Joule’s experiment was ground breaking because he demonstrated that we can heat water without using fire. He put water in a glass with a thermometer to monitor the increase in heat. Then he added a paddle system and turned it vigorously. After a while he realized that the water temperature had increased. Infect he repeated this experiment many times with different systems and always reached the conclusion that 4.19 Joule of work was required to raise the temperature of 1 gram of water by 1 degree Celsius.

A BTU is the amount of heat needed to raise temperature of one pound of water by one degree Fahrenheit.

1 BTU = 1,000 joules

A calorie is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius.

1 calorie (cal) = 4.186 Joules

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