# Length and Distance

## Length refers to the measurement of an object from one end to another, while distance is the space between two objects or points. The two systems used to measure length and distance are the English and metric systems.

###### Asked in Units of Measure, Length and Distance

### What instrument measures length or distance?

It depends on the meaning of length. Typically it means a unit
of distance but it can also be applied to the passage of time, such
as the duration of a piece of music. Thus a time-piece, such as a
stopwatch, would be the instrument of choice when measuring a
length of time.
For units of distance, there are a huge number of instruments
available:
Calipers and micrometers
Rulers and meter or yard sticks or line gauges
tape measures,
surveyor's wheels,
micrometers,
rangefinders
laser rules.
Walking wheels
RADAR
SONAR
LIDAR
Which instrument you use largely depends on how accurate the
result needs to be (the tolerance), combined with the size of the
object or the distance being measured. Generally, the greater the
distance, the greater the tolerance.
Measuring tapes are more flexible than straightedge rulers and
can accurately measure much greater distances, typically up to 10m.
Today, they are made from cloth or fiberglass (such as a tailor's
measure) or from a stiff, curved metallic ribbon that can retract
into a coil (such as a carpenter's or constructor's measure).
Surveyor's tapes are often made from durable plastic or fiberglass
and allow more accurate measuring over much greater distances,
usually up to 100m or more.
Micrometers are used when measuring the size of distant objects.
Modern micrometers are often GPS-based systems used to perform
geodetic measurements.
Micrometers and calipers are generally used in engineering
applications where straightedge rulers would be impractical, such
as when measuring the diameter of a column or when measuring the
gauge of a threaded bolt.
Laser rulers are a new type of measuring device, designed to
specifically measure the distance to an object, where a laser beam
can be reflected back to the device. Handheld devices are generally
low-power devices so their accuracy is limited to within 100m or
so, but more powerful lasers can measure greater distances,
including the distance to the moon (where reflectors were
specifically placed during the moon landings in the late 60's and
early 70's).
In microscopes, there is commonly a glass slide marked with an
engraving that goes down to a few microns (micrometer
scale). The glass slide with the engraved lines is known as a
graticule or reticule).
To measure distance traveled, a pedometer is carried by walkers
to measure distance walked. An Odometer is fitted to vehicles,
including bicycles, to measure distances traveled (miles or
kilometers).
You may use a ruler.
Examples of common instruments used for measuring length are the
ruler, (for measuring milimeters, centimeters, inches, and 1 foot),
the yardstick, (which is 3 feet long, [36 inches], and measures
milimeters, centimeters, inches, and about 1 meter, {3.28084
feet}). There are also tape measurers that can measure all of the
previously listed measurements and vary on the longest length they
can measure. Units of length are based on feet or meters. Tools for
measuring length range from simple rulers to lasers. A ruler
I would say a ruler or a tape measure.

###### Asked in Units of Measure, Length and Distance

### How many centimetres are there in 8.5 inches?

21.59 centimeters.
Solution:
1. 2.54 centimeters = 1 inch. You can express this as the
fraction 2.54 cm / 1 inch (read aloud as "2.54 centimeters per
inch")
2. To convert 8.5 inches to centimeters, cancel the inches in
the numerator and denominator & multiple 2.54 * 8.5 = 21.59 cm
(see below. Note: Disregard the _ character. It is only included to
make the fractions align properly for easier viewing.
2.54 cm__8.5 inches___ 21.59 cm
--------- * ----------- = ----------- = 21.59 cm
1 inch_______1__________1

###### Asked in Math and Arithmetic, Area, Length and Distance

### How many square feet is one acre?

The area of one acre is 43,560 square feet, but there are an
infinite number of different shapes and dimensions an acre could
have.
Here are a few examples:
Square: 208.71 feet on a side (approx.)
Rectangles:
9' x 4840'
10' x 4356'
12' x 3630'
20' x 2178'
24' x 1815'
40' x 1089'
60' x 726'
72' x 605'
120' x 363'
121' x 360'
180' x 242'
Circle: 235.5-ft diameter (approx.)
All 13 of these examples have areas of 1 acre.
One Acre = 43560 sq ft

###### Asked in Units of Measure, Length and Distance

### How many meters are in one kilometer?

There are 1000 meters in a kilometer.
The prefix kilo- means "1000".
Examples:
kilogram is one thousand grams
kilohertz is one thousand oscillations per second
kilovolt is one thousand volts
kilobyte is roughly one thousand bytes of storage (used
because 210, or 1024, is the power of two closest to 1000 bytes: it
is easily close enough to one thousand, or one kilo-, for
describing computer storage in general terms).

###### Asked in Length and Distance

### How many millimeters are in a centimeter?

There are 10 millimeters in 1 centimeter.
Prefix 'milli' is used to denote sub multiples of meter and uses
factor 0.001.
Prefix 'centi' is used to denote sub multiples of meter and uses
factor 0.01.
Factor difference of 10 (0.01 / 0.001 = 10) shows that there are
10 millimeters in one centimeter.
10
ten
1 cm = 10 mm
Ten (10).

###### Asked in Math and Arithmetic, Photography, Length and Distance

### How many pixels are in a 2 feet by 2 feet photo?

That would depend on the resolution of the printing. If for
example, it is 100 pixels per inch, then 2 ft = 24 in (times 100
pix per inch) = 2400 x 2400 = 5,760,000
*****
From a mathematical perspective, the answer is sound. From a
photography perspective, the asker should know that it is a
relationship between the "resolution" that the image was taken at
versus the size of the viewed image. The reason for the quotes is
in my last sentence.
In a 640x320 image (A), there are twice as many pixels in both
directions than one of 320x160 (B). Therefore, the A image is twice
the length and height as the B image and the pixels and spaces
between are no different in size from one picture to the other.
Thus there is no difference in the eye's ability to "resolve" the
spaces in between for a given viewing distance. What does matter is
the size that the images are rendered at. To make this as simple as
possible, it is best to compare photographs printed from these two
images. An 8x10 from A will look better because there are more
pixels crammed in a given inch than there will be in picture B,
thus your eye's ability to resolve the spaces between them is not
as good.
So how many pixels are in an inch for a GIVEN photo size depends
on the "resolution" of the image file versus the size it is viewed
at. The "resolution of the printing" is a matter for the printer or
machine that creates the print, and that is another animal
altogether.
The problem is, pixel count is not supported as a measure of
digital photograph resolution by international standards even
though it is used by just about everybody. Hopefully, my answer
sheds some light as to why.

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