Name: unit conversion steps and real-world errors
Uploaded: 2023-04-30T10:48:05.000Z
Duration: 1 min 36 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Physical Science

PS.1

PS.1.b

Conversion of Units

La conversion d’unité est le processus de conversion d’unités d’une unité à une autre.
Le système d’unités SI est l’unité standard universellement acceptée pour les grandeurs physiques. Mais quelques pays, dont les États-Unis, utilisent parfois un ensemble différent d’unités appelées unités anglaises.
Souvent, une seule grandeur physique peut être exprimée dans des unités différentes mais équivalentes. Par exemple, la longueur d’un objet peut être exprimée en mètres ou en centimètres, où 1 mètre représente la même longueur que 100 centimètres ou la masse d’un objet peut être exprimée en grammes ou en kilogrammes, où 1 kilogramme équivaut à 1000 grammes.
La conversion entre ces unités équivalentes est facilitée au moyen d’un facteur de conversion d’unité.
Par exemple, la longueur en mètres ou en centimètres peut être interconvertie, à l’aide de facteurs de conversion : 1 mètre par 100 centimètres et 100 centimètres par 1 mètre. Le rapport de choix dépend de l’unité souhaitée dans le résultat.
Prenons l’exemple d’une girafe de 500 centimètres de haut. Pour exprimer sa hauteur en mètres, les nombres et les unités doivent être multipliés par le facteur de conversion approprié.
Les nombres donnent la quantité de produit, 5, et les unités s’annulent, à l’exception des mètres. Ainsi, la hauteur de la girafe est égale à 5 mètres.

conversion des unités

Parfois, il est nécessaire de convertir d'une unité à une autre. Par exemple, lire un livre de cuisine dans lequel les quantités sont exprimées en litres ou en onces peut nécessiter la conversion des quantités en tasses. Ou encore, lorsque nous recherchons les directions pour nous rendre à un endroit, nous pouvons être intéressés de savoir combien de miles nous allons marcher. Dans ce cas, nous devrions convertir les unités de pieds ou de mètres en miles.

La première étape de la conversion des unités consiste à répertorier les unités données et les unités requises pour la conversion. La deuxième étape consiste à déterminer un facteur de conversion liant l'unité donnée et l'unité requise. Le facteur de conversion est défini comme le rapport qui exprime dans quelle mesure une unité est égale à une autre unité. Par exemple, il y a 1 000 mètres dans 1 kilomètre. Lors de la conversion, veillez à ce que les unités dans la conversion correspondent.

Un exemple bien connu de l'importance de la conversion des unités est l'orbiteur climatique de Mars. La NASA a lancé cette sonde le 11 décembre 1998. Cependant, le 23 septembre 1999, la NASA a perdu le contact avec la sonde alors qu'elle tentait de la guider vers son orbite prévue autour de Mars. Des enquêtes ultérieures ont révélé que les unités dans les deux programmes utilisés pour enregistrer et piloter le propulseur étaient désynchronisées. Cette erreur a fait en sorte que la sonde a suivi une trajectoire très différente de celle que la NASA avait projetée, la faisant brûler dans l'atmosphère martienne ou la faire partir dans l'espace. Cette négligence de la conversion des unités a coûté des centaines de millions de dollars, sans parler du temps passé sur le projet par les scientifiques et les ingénieurs.

Ce texte est adapté de <a href="https://openstax.org/books/university-physics-volume-1/pages/1-3-unit-conversion">Openstax, University Physics Volume 1, Section 1.3: Unit Conversion</a>.

Conversion des unités

Parfois, il est nécessaire de convertir d’une unité à une autre. Par exemple, la lecture d’un livre de cuisine dans lequel les quantités sont exprimées en litres ...

Education

Enseignement

JoVE Core

Physics

Physique

Unit 1

Unité 1

Units, Dimensions, and Measurements

Unités, dimensions et mesures

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

unit conversion steps and real-world errors

Unit conversion lets you change a measurement from one unit to another. It is useful in everyday life, such as when a cookbook gives amounts in liters or ounces and you need cups instead. It also helps when directions use feet or meters, but you want to know the distance in miles.

The first step is to list the given unit and the unit you need. The second step is to choose a conversion factor, which is a ratio that shows how many of one unit equal another unit. For example, 1,000 meters equal 1 kilometer.

During the conversion, the units must cancel correctly. This keeps the calculation organized and gives the right final unit. Unit conversion is important in science and engineering because small unit mistakes can lead to major problems.

A well-known example is the Mars Climate Orbiter. NASA launched the probe on December 11, 1998, and lost contact with it on September 23, 1999 while trying to place it in orbit around Mars. Investigators found that the two programs used different units for recording and driving the thruster. That mismatch sent the probe on the wrong path, where it burned up in the Martian atmosphere or flew out into space. The error cost hundreds of millions of dollars and much time for the scientists and engineers involved.

Unit Conversion Steps and Real-World Errors

unit-conversion-steps-and-real-world-errors

the scope of physics

How Physics Shapes Science and Technology

Physics studies the interactions of energy, matter, space, and time. It looks for the basic mechanisms that explain natural phenomena. The word physics comes from the Greek word physis, which means nature. Physics helps us understand the natural world at its most fundamental level. It relies on quantitative laws, or rules written in numbers and measurements, to describe how things behave. That approach can also help other fields improve the limits of current technology. Physics matters in...

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models, theories, and laws

Scientific Models, Theories, and Laws

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units and standards of measurement

SI Units for Physical Quantities

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estimation of the physical quantities

Fermi Estimation for Physical Quantities

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base quantities and derived quantities

SI Base Units Behind Measured Quantities

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conversion of units

Unit conversion lets you change a measurement from one unit to another. It is useful in everyday life, such as when a cookbook gives amounts in liters or ounces and you need cups instead. It also helps when directions use feet or meters, but you want to know the distance in miles. The first step is to list the given unit and the unit you need. The second step is to choose a conversion factor, which is a ratio that shows how many of one unit equal another unit. For example, 1,000 meters equal 1...

accuracy and precision

Repeated Measurements in Science

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random and systematic errors

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rules for significant figures

Measurement Precision and Significant Figures

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significant figures in calculations

Rounding Rules for Significant Figures

Rounding rules for significant figures help show the right level of certainty in measured results. When a calculation is reported with the correct number of significant figures, it better matches the uncertainty in the measurements. The rounding rule depends on the type of math being done. For addition and subtraction, the result should have the same number of decimal places as the number with the fewest decimal places. For multiplication and division, the result should have the same number of...

dimensional analysis

Dimensional Checks in Physics Equations

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problem solving: dimensional analysis

Dimensional Checks for Physics Equations

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solving problems in physics

Physics Problem Solving: Strategy to Check

Physics problem solving uses general physical principles to work out specific situations. It is a key skill in physics, and it can also help with everyday life. The same analytical skills can be used in new situations, while a list of facts can never cover every possible case. Solving physics problems also takes creativity and insight. These skills grow with experience and practice. There is no simple step-by-step method that works for every problem, but a three-stage process can guide the...

key terms and concepts

Learn how to convert units using conversion factors, unit cancellation, and clear steps. See how a unit mismatch helped cause the Mars Climate Orbiter failure.

Unit Conversion Steps and Real-World Errors | JoVE K12

physics

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PH.1

PH.1.b

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.1

CHEM.1.E

Scientific Method

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Hypothesis Test for Test of Independence

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Decision Making: P-value Method

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First, a ...

Decision Making: Traditional Method

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empirical-method-to-interpret-standard-deviation

Empirical Method to Interpret Standard Deviation

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Solving Problems in Physics

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The student will demonstrate an understanding of scientific and engineering practices by asking questions and defining problems
• ask questions that require empirical evidence to answer
• develop hypotheses indicating relationships between independent and dependent variables
• offer simple solutions to design problems

PS.1.a

What is an Experiment?

An experiment is a planned activity carried out under controlled conditions. The purpose of an experiment is to investigate the relationship between two ...

Study Design in Statistics

A study design is a set of techniques that allow a researcher to collect and analyze data from different variables defined for a specific research ...

Observational Studies

Observational studies are a type of analytical study where researchers observe events without any interventions. In other words, the researcher does not ...

Experimental Designs

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Randomized Experiments

The randomization process involves assigning study participants randomly to experimental or control groups based on their probability of being equally ...

Crossover Experiments

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Controls in Experiments

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Bias

Bias refers to any tendency that prevents a question from being considered unprejudiced. In research, bias occurs when one outcome or answer is selected ...

Blinding

Blinding is a commonly used method of not telling participants which treatment a subject is receiving. Blinding is a critical part of a randomized control ...

Clinical Trials

Clinical trials are prospective experimental studies conducted on humans to determine the safety and efficacy of treatments, drugs, diet methods, and ...

Data Collection by Observations

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Data Collection by Survey

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Units and Standards of Measurement

A physical quantity is defined either by specifying its measurement method or by stating how it is calculated from other measurements. For example, ...

Estimation of the Physical Quantities

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Base Quantities and Derived Quantities

In any system of units, the units for some physical quantities must be specified through a measurement process. These measurements are the base quantities ...

Sometimes, there is a need to convert from one unit to another one. For instance, reading a cookbook in which quantities are expressed in units of liters ...

The student will demonstrate an understanding of scientific and engineering practices by planning and carrying out investigations
• independently and collaboratively plan and conduct observational and experimental investigations; identify variables, constants, and controls where appropriate and include the safe use of chemicals and equipment
• evaluate the accuracy of various methods for collecting data
• take metric measurements using appropriate tools and technologies
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Review and Preview

Data are individual items of information obtained from a population or sample. Data may be classified as qualitative (categorical), quantitative ...

What is a Frequency Distribution

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Ogive Graph

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Histogram

The histogram is a graphical representation in the x-y form of data distribution in a data set. The horizontal x-axis is labeled with what the data ...

Relative Frequency Histogram

The relative frequency depicts the proportion of data points that have each value. The frequency tells the number of data points that have each value. ...

Scatter Plot

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Time-Series Graph

A time-series graph is a line graph with repeated measurements taken at successive intervals of time. It is also called a time series chart. To construct ...

Bar Graph

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Multiple Bar Graph

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Pareto Chart

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Pie Chart

A pie chart (or a pie graph) is a circular graphical chart or a pictorial representation of categorical data. It is divided into slices of pie each ...

What is Central Tendency?

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What is Variation?

Apart from the measures of central tendency, distribution, outliers, and the changing characteristics of data with time, an important characteristic of ...

Range

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Standard Deviation

The most commonly used measure of variation is the standard deviation. It is a numerical value measuring how far data values are from their mean. The ...

Calculating Standard Deviation

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Variance

&#160;The deviations show how spread out the data are about the mean. A positive deviation occurs when the data value exceeds the mean, whereas a negative ...

Coefficient of Variation

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Contingency Table

A contingency table provides a way of portraying data that can facilitate calculating probabilities. It is a method of displaying a frequency distribution ...

Statistical Analysis: Overview

An analysis is usually conducted by replicated sampling or repeated measurements on the same sample. This leads to scattered results rather than a single ...

The student will demonstrate an understanding of scientific and engineering practices by pnterpreting, analyzing, and evaluating data
• construct and interpret data tables showing independent and dependent variables, repeated trials, and means
• construct, analyze, and interpret graphical displays of data and consider limitations of data analysis
• apply mathematical concepts and processes to scientific questions
• use data to evaluate and refine design solutions to best meet criteria

PS.1.c

Models, Theories, and Laws

Scientists frequently use models to help them comprehend a specific collection of phenomena. In physics, a model is a condensed version of a physical ...

Inductive Reasoning

Inductive reasoning is a form of logical thinking that uses related observations to arrive at a general conclusion. It is uncertain and operates in ...

Deductive Reasoning

Deductive reasoning, or deduction, is the type of logic used in hypothesis-based science. In deductive reasoning, the pattern of thinking moves in the ...

The student will demonstrate an understanding of scientific and engineering practices by constructing and critiquing conclusions and explanations
• construct scientific explanations based on valid and reliable evidence obtained from sources (including the students' own investigations)
• construct arguments supported by empirical evidence and scientific reasoning
• generate and compare multiple solutions to problems based on how well they meet the criteria and constraints
• differentiate between a scientific hypothesis, theory, and law

PS.1.d

The student will demonstrate an understanding of scientific and engineering practices by developing and using models
• construct, develop, and use models and simulations to illustrate and/or explain observable and unobservable phenomena
• evaluate limitations of models

PS.1.e

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

The student will demonstrate an understanding of scientific and engineering practices by obtaining, evaluating, and communicating information
• read scientific texts, including those adapted for classroom use, to determine the central idea and/or obtain scientific and/or technical information
• gather, read, and synthesize information from multiple appropriate sources and assess the credibility, accuracy, and possible bias of each publication
• construct, use, and/or present an oral and written argument supported by empirical evidence and scientific reasoning

PS.1.f

Unit Conversion Steps and Real-World Errors

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