Archimedes (ca. 287–212 BC), the great Sicilian inventor, physicist, mathematician, and engineer, is credited with saying, "Give me a place to stand and I will move the earth." He understood the concept of using simple machines to gain a mechanical advantage to move or lift heavy objects with less force.

The first simple machines were probably wooden levers used to move large boulders and sharp rocks used as wedges to scrape off the skins of dead animals. Around 3,000 BC, logs were used as rollers to move heavy objects. This concept developed into the wheel and axle simple machine. Some 200 years later, the builders of Stonehenge used levers, rollers, and pulleys. Soon afterward, inclined planes, ramps, and rollers were used to build the Great Pyramids of Egypt. Progress continued with the development of the screw principle by Archimedes in the third century BC. Early civilizations throughout the world continued to develop and invent simple machines to construct their buildings and facilitate work. Progress was steady throughout the next 20 centuries—with the invention of the spinning wheel, compass, printing press, telescope, mechanical clock, and engine—but it was given a big leap forward by improvements to the steam engine by James Watt of England in the mid-eighteenth century. That ushered in the Industrial Revolution and the machine age for modern man.

### Physical Science Definitions and Formulas

**Force **is generally thought of as a push, pull, dropping, stretching, or squeezing of an object that results in a change in the shape and/or a change in the motion of the object. Examples of forces include gravity, magnetism, and electricity.

Force is measured in the SI (System International), or metric system, in units called Newtons (N), for the great English mathematician and physicist Isaac Newton (1642–1727). In the British system of measurement, force is measured in pounds × foot.

Force (F) = Mass (M) × Acceleration (A)

**Mass **is the quantity of matter of an object. In the metric system, the unit of measurement of mass is the kilogram (kg).

**Weight **is a force originating when a mass is acted on by gravity. Weight (W) is the product of an object's mass (m) and the acceleration of gravity (g) at the location of the object, or W = mg. The units of weight in the SI are Newtons. Weight is also measured by the gram in the metric system and by the ounce or pound in the British system.

**Velocity **is a measure of how fast an object is moving in a given direction. In the metric system, velocity is measured in meters per second (m/s). In the British system, the measurement is in miles per hour (mph).

**Momentum **is the term used when mass has a velocity. Its unit of measure has no metric or British name.

Momentum = Mass × Meters/Second

**Acceleration **is the rate of change of velocity. The metric unit of measure for acceleration is meters per second per second (m/s/s). The British system measures acceleration in feet per second per second (ft/s/s).

**Length **is measured in meters (m) in the metric system. In the British system, length is measured in feet (ft).

**Newton **is a measure of the amount of force required to accelerate a mass of one kilogram (kg) at a rate of one meter (m) per second (s) per second (s).

1 N = 1 kg × m/s/s

**Friction **is a force that reduces the motion of objects. It occurs when two objects rub against each other with heat as a byproduct. Friction is reduced by polishing a surface and by using lubricants (oils and greases) and rollers to allow objects to move more easily.

**Work **is the use of force to cause motion. It is the transfer of energy through motion. Energy (work) can never be destroyed; it can only be transferred. For work to take place, a force must be exerted through a distance. The amount of work performed depends on the amount of force that is exerted and the distance over which the force is applied.

Work (W) = Force (F) × Distance (D)

Mechanical work is measured by the joule (J), named after the nineteenth century English physicist James Prescott Joule. (One joule is equal to 1 Newton multiplied by 1 meter.)

1 J = 1 N ×1 m

The British system measures mechanical work in foot-pounds (ft-lb).

**Torque **is a twisting force that occurs when the force is not applied to the object's center of mass.

**Power **is the rate at which work is performed. It is derived by measuring work per unit of time. The metric system unit used to measure power is the Watt (W). One watt is equal to 1 joule per second.

1 W = 1 J/s

1000 Watts = 1 Kilowatt (KW)

The British unit of measurement for power is the horsepower (HP).

1 HP = 550 ft-lb/s = 746 watts

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