General Physics 1 – Units of Measurement

These flashcards review the key concepts from the lecture on units of measurement, covering the need for standards, SI base and derived units, modern definitions, prefixes, and basic unit conversion principles.

What caused Air Canada Flight 143 to run out of fuel on July 23, 1983?

Confusion and human error involving different units of fuel measurement.

Why did NASA’s Mars Climate Orbiter mission fail in 1999?

A navigation error from failing to convert English (imperial) units to metric (SI) units.

What is meant by “measurement”?

The process of assigning a numerical value to a property of an object by comparing it with a standard.

Why is a standard system of measurement important?

It provides a fundamental, stable, and universal reference so that results are consistent and comparable.

What is the International System of Units (SI) commonly called?

The metric system.

In what year was the SI system formally established?

1960.

Name the seven SI base units.

Second (s), meter (m), kilogram (kg), ampere (A), kelvin (K), mole (mol), and candela (cd).

What is the SI base unit for time and its symbol?

Second (s).

What is the SI base unit for length and its symbol?

Meter (m).

What is the SI base unit for mass and its symbol?

Kilogram (kg).

What is the SI base unit for electric current and its symbol?

Ampere (A).

What is the SI base unit for thermodynamic temperature and its symbol?

Kelvin (K).

What is the SI base unit for amount of substance and its symbol?

Mole (mol).

What is the SI base unit for luminous intensity and its symbol?

Candela (cd).

How is one second defined in SI?

The duration of 9 192 631 770 cycles of microwave radiation corresponding to the transition in cesium-133 atoms.

How is one meter defined in SI?

The distance light travels in vacuum in 1 ⁄ 299 792 458 of a second.

How was the kilogram redefined in 2019?

By fixing the Planck constant h at 6.626 070 15 × 10⁻³⁴ J·s (kg m² s⁻¹).

On what constant is the modern definition of the ampere based?

The elementary charge e fixed at 1.602 176 634 × 10⁻¹⁹ C.

On what constant is the kelvin definition based?

The Boltzmann constant k fixed at 1.380 649 × 10⁻²³ J K⁻¹.

How is one mole defined?

It contains exactly 6.022 140 76 × 10²³ elementary entities (Avogadro constant).

On what physical quantity is the candela definition based?

The luminous efficacy of monochromatic radiation of 540 × 10¹² Hz fixed at 683 lm W⁻¹.

What is a derived quantity?

A physical quantity expressed as a product or quotient of two or more base units.

State the SI derived unit and formula for force.

Newton (N) = kg m s⁻².

State the SI derived unit and formula for energy or work.

Joule (J) = kg m² s⁻² or N m.

Which SI prefix represents 10⁹?

Giga (G).

Which SI prefix represents 10⁻⁶?

Micro (µ).

Which SI prefix represents 10¹²?

Tera (T).

Why must units in an equation be converted to a common system?

To keep the equation dimensionally consistent and avoid calculation errors.

What is the general method for converting one unit to another?

Multiply by a conversion factor arranged so the undesired unit cancels, leaving the desired unit.