Small Quantities in Calculations
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Questions and Answers

What determines whether a small quantity can be omitted from consideration in calculations?

  • Its relative minuteness compared to other quantities. (correct)
  • Its absolute size.
  • The units it is measured in.
  • Whether it involves time or money.

A quantity that is considered small in comparison to one value will always be considered small, regardless of the reference value.

False (B)

What term did people in Queen Elizabeth's days use for the subdivisions of a minute, and what does it literally mean?

Second minutes, small quantities of the second order of minuteness.

If 1/100 is considered a small fraction, then 1/10,000 would be considered a small fraction of the ______ order of smallness.

<p>second</p> Signup and view all the answers

Match the following fractions with their order of smallness, assuming 1/100 is a 'small fraction'.

<p>1/100 = Small Fraction 1/10,000 = Second Order of Smallness 1/1,000,000 = Third Order of Smallness</p> Signup and view all the answers

What concept is often confused with the second order of smallness by mathematicians?

<p>The second order of magnitude. (A)</p> Signup and view all the answers

According to the examples given, a minute is a relatively small quantity of time when compared to a week.

<p>True (A)</p> Signup and view all the answers

Explain the relationship between a 'minute,' a 'second minute,' and a 'second' in the context of historical time measurement.

<p>A minute was initially considered a small fraction of an hour. A 'second minute' was a further subdivision of the minute into 60 smaller parts. The term 'second minute' was later shortened to 'second'.</p> Signup and view all the answers

In the context of calculus, what is the primary reason for neglecting small quantities of the second order or higher?

<p>Their effect becomes negligible compared to first-order small quantities. (C)</p> Signup and view all the answers

If dx represents a small quantity, then x * dx is always negligible.

<p>False (B)</p> Signup and view all the answers

Explain, in your own words, the difference between a small quantity of the first order and a small quantity of the second order.

<p>A small quantity of the second order is a small fraction of an already small quantity (of the first order), making it much smaller and often negligible in calculations.</p> Signup and view all the answers

In calculus, a small bit of x is represented by the term ______.

<p>dx</p> Signup and view all the answers

Match the mathematical expressions with their corresponding order of smallness, given that dx is a small quantity:

<p>dx = First order dx * dx = Second order x * dx = First order (if x is finite) dx * dx * dx = Third order</p> Signup and view all the answers

Why might a very small quantity still be important in a calculation?

<p>If it is multiplied by a very large quantity. (B)</p> Signup and view all the answers

If we consider 1/1,000,000 as 'small', then 1/1,000,000,000,000 is a small quantity of the second order and can typically be disregarded in comparison.

<p>True (A)</p> Signup and view all the answers

Explain the geometric illustration provided using a square (Figure 1) to demonstrate the concept of small quantities and their orders.

<p>The initial square represents $x^2$. When $x$ grows by a small increment $dx$, the area increases by $2x \cdot dx$ (first order) and $(dx)^2$ (second order). The smaller $dx$ is, the less significant $(dx)^2$ becomes compared to $2x \cdot dx$.</p> Signup and view all the answers

The text uses the analogy of a millionaire, his secretary, and the secretary's boy to illustrate the concept of ______ of smallness.

<p>orders</p> Signup and view all the answers

What analogy does the text use from Dean Swift to illustrate the concept of small quantities?

<p>Fleas having smaller fleas that prey on them (A)</p> Signup and view all the answers

Flashcards

Small quantities

Quantities considered negligible when compared to larger ones.

First order smallness

The smallest level of quantity that can be significant in calculations.

Second order smallness

A small quantity that is negligible compared to first order smallness.

Differentials

Symbols like dx, representing small changes in variables in calculus.

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Negligible quantities

Quantities so small they can be ignored in calculations.

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x⋅dx

An example of a first-order product, which can be significant in calculations.

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(dx)²

A second order small quantity that is usually negligible.

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First-order vs Second-order terms

First-order terms are significant; second-order terms are often ignored.

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Growth of x

When variable x increases by a small amount dx, affecting its square.

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Proportional fractions

Small parts taken from larger quantities, revealing significant differences.

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Minute

A small unit of time, 1/60 of an hour.

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Second

A smaller unit of time, 1/60 of a minute.

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Relative minuteness

How small a quantity is compared to another.

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Small fraction

A numeric value perceived to be minor in significance.

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Second order of smallness

A small fraction of a small fraction.

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Farthing

An old coin, very small in value compared to a sovereign.

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Sovereign

A gold coin of considerable value.

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Third order of smallness

A small fraction of a second-order small fraction.

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Study Notes

Small Quantities in Calculations

  • Small quantities, varying in degree, are common in calculations.
  • Determining when to disregard a small quantity depends on its relative size (minuteness).
  • Time units illustrate relative minuteness:
    • A minute is small compared to a week.
    • A second (second order of smallness) is even smaller compared to a day or a week.
    • The concept of "minute" and "second" originates from their fractions of larger units.

Orders of Smallness

  • Relative size is key: a farthing is small relative to a sovereign, but negligible relative to a large sum like £1000.
  • Defining a "small" fraction allows establishing smaller orders:
    • If 1/60 is small, then (1/60) * (1/60) (1/3600) is a second-order smallness.

Importance in Precise Measurements

  • Extremely precise measurements (e.g., a chronometer error of 0.5 minutes per year) require considering extremely small quantities.
    • One millionth (1/1,000,000) is small for these purposes; and further orders (one billionths) are extremely negligible in comparison.
  • The smaller the first-order small quantity, the more negligible the second-order quantity becomes.
    • Small order quantities can still become important if multiplied by a large factor.

Differentials and Higher-Order Smallness

  • In calculus, dx, du, dy represent small changes.
  • Small quantities, such as x ⋅ dx or x 2 ⋅ dx, might not be considered negligible if not multiplied by another small fraction.
  • (dx)2 (or a quantity raised to a higher power) is always considered a smaller/negligible quantity in the context of a small change.

Visual Representation (Geometric Example)

  • Imagine enlarging a square by dx on each side.
  • The added areas (2 * x * dx) are first-order small quantities.
  • The tiny corner square ((dx)2) is a second-order small quantity and becomes negligible in comparison with the first order if dx is itself a sufficiently small value.

Analogy and Further Explanation

  • Analogy of a millionaire, his secretary, and a boy receiving portions.
  • Smaller portions of decreasing significance/order demonstrate that second order (or smaller) quantities are very negligible in proportion to first order quantities.
  • Emphasizes that even something small (dx) could be further divided/made smaller and smaller and become insignificant.

Example from Nature

  • Illustrates how successive orders of smallness exist in nature.
    • An ox cares little about a flea, but even less about a flea's flea (the second-order smallness).
  • This principle of successive smallness holds true across various fields.

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Description

This text explains how to deal with small quantities in calculations, emphasizing the importance of relative size. It also explains different orders of smallness, using time units as examples. It concludes by highlighting the significance of considering extremely small quantities in precise measurements.

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