1.2 Physical Quantities and Units Flashcards
all physical quantities can be expressed as combinations of only four fundamental physical quantities:
- length (meters)
- mass (kilograms)
- time (seconds)
- electric current (amperes).
There are two major systems of units used in the world:
SI units (also known as the metric system) and English units (also known as the customary or imperial system).
_______ were historically used in nations once ruled by the British Empire and are still widely used in the United States.
English units (customary or Imperial system)
the standard system agreed upon by scientists and mathematicians; and used by virtually every country in the world except United States.
SI units
(part of the metric system)
The acronym “SI” is derived from the French Système International.
algebraic combinations of the fundamental units
derived units
The fundamental unit of time, the second, is based on ____ clocks.
atomic
An atomic clock uses the vibrations of cesium atoms to keep time to a precision of better than a microsecond per year.
In 1983, the meter was given its present definition (partly for greater accuracy) as:
the distance light travels in a vacuum in 1/299,792,458 of a second.
This change defines the speed of light to be exactly 299,792,458 meters per second. The length of the meter will change if the speed of light is someday measured with greater accuracy.
_____: the mass of a platinum-iridium cylinder kept with the old meter standard at the International Bureau of Weights and Measures near Paris.
kilogram
_____: a system in which values can be calculated in factors of 10
metric system
The term ________ refers to the scale of a value expressed in the metric system.
order of magnitude
10^1, 10^2, 10^3 are all different ____
orders of magnitude
All quantities that can be expressed as a product of a specific power of 10 are said to be of the same _____
order of magnitude
_________ can be thought of as a ballpark estimate for the scale of a value. The diameter of an atom is on the order of 10−9 m, while the diameter of the Sun is on the order of 109 m.
Order of magnitude
10^0 =
1
10^1 =
10
10^3 =
1000
10^-1 =
0.1
10^-2 =
0.01
Some hummingbirds beat their wings more than 50 times per second. A scientist is measuring the time it takes for a hummingbird to beat its wings once. Which fundamental unit should the scientist use to describe the measurement? Which factor of 10 is the scientist likely to use to describe the motion precisely? Identify the metric prefix that corresponds to this factor of 10.
fundamental unit of seconds
milliseconds
10^-2
One cubic centimeter is equal to one milliliter. What does this tell you about the different units in the SI metric system?
The fundamental unit of length (meter) is probably used to create the derived unit of volume (liter). The measure of a milliliter is dependent on the measure of a centimeter.
The four fundamental units are?
- meter (m)
- kilogram (kg)
- second (s)
- ampere (A)
Unit conversions involve changing a value expressed in one type of unit to another type of unit. This is done by using _________, which are ratios relating equal quantities of different units.
conversion factors
The speed limit on some interstate highways is roughly 100 km/h. (a) What is this in meters per second? (b) How many miles per hour is this?
a) = 27.8 m/s
100 km/h x 1000m / 1km = 100,000 m/h
100,000 m/h x 1 / 3600s = 100,000 / 3600 m/s
1000 / 36 m/s
b) = 62.1 miles / h
100 km/h * 0.621 miles
A car is traveling at a speed of 33 m/s. (a) What is its speed in kilometers per hour? (b) Is it exceeding the 90 km/h speed limit?
33m x 1km / 1000m = 0.033 km/s
.033 km/s * 3600s = 118.8 km/h
yes it is
