Topic 0a: Fundamental Units and Conversions

0a: Fundamental Units and Conversions

Learning Targets

• Identify the fundamental units that will be used in Physics and distinguish between a fundamental unit and a derived unit.

• Use SI prefixes and rewrite using standard and scientific notation.

• Perform unit conversions in both English and SI units using dimensional analysis

Reference: College Physics for AP Courses by OpenStax, Sections 1.1, 1.2

Start

What is Physics?

• Galaxies are big, atoms are small, the laws of physics describe both - There is an underlying unity within the diverse universe.

• The laws of physics are relatively few - There is an underlying simplicity to the complex universe.

• The role of Physics is to investigate and explain the underlying unity and simplicity of a diverse and complex universe.

• Classical Physics - not an exact description of the universe, but a good approximation when objects are
• moving less than 1% the speed of light,
• large enough to be seen with a microscope,
• acted on by weak gravitational fields.

• Modern Physics - Includes the Theory of Relativity (covers very fast things and very strong gravitational fields) and Quantum Mechanics (covers very small things)

Fundamental Units

1. Within your group, list 8 physical quantities you could measure to describe things in this room. (For example, you might measure the length of a desk, the weight of a chromebook, or the heat a piece of paper would give off it were set on fire)

Weight of a chair, Height of the ceiling, Length of the counter, Speed of a person, Temperature of the floor, Strength of a piece of paper, Time it takes to walk around the room, Brightness of the lights

Fundamental Units

A physical quantity is defined by how it is measured or how it is calculated.

Quantities are expressed in standardized units to allow for comparison so that patterns can be seen.

Fundamental Units - all other units are defined based on these

Fundamental Units

Metric Prefixes

Prefixes are placed in front of units to express the order of magnitude of the measurement.

Metric Prefixes

The chart above explains the relationship of the prefix to the basic unit (like meters or grams) 1 meter = ____________ kilometers or 1 Megameter = _____________ meters

Metric Prefixes

Convert Units using dimensional analysis (also known as the factor-cancel process) Draw a large “plus sign” and place the initial quantity with units at the left side top. Then arrange conversions so that units will cancel from top to bottom until the unit that is left is what you want. It is easiest to convert to a fundamental unit and then to a new unit prefix.

Metric Prefixes

Example 1: Convert 388,215 micrometers to hectometers

Unit Conversions

Derived Units can be converted and converted from metric to English or English to metric using the same factor and cancel process.

Unit Conversions

On the right side, place a conversion factor such that the unwanted unit will cancel. Repeat as necessary.

Example 1: Convert 27.3 cm to inches

Unit Conversions

On the right side, place a conversion factor such that the unwanted unit will cancel. Repeat as necessary.

Example 2: Convert 20 centimeters per second (cm/s) into kilometers per hour (km/h)

Unit Conversions

On the right side, place a conversion factor such that the unwanted unit will cancel. Repeat as necessary.

Example 3: Convert 20 square feet (ft2) into square meters (m2)

The End

Order of Magnitude

How relatively large or small a measurement is

Distancedescribe by how it is measured - one meter is the distance light travels in 1/299 782 458th of a second Average Speed described by how it is calculated - distance traveled divided by the time of travel