1.2 Physical Quantities and Units

Question 1

all physical quantities can be expressed as combinations of only four fundamental physical quantities:

Answer 1

1. length (meters)
2. mass (kilograms)
3. time (seconds)
4. electric current (amperes).

Question 2

There are two major systems of units used in the world:

Answer 2

SI units (also known as the metric system) and English units (also known as the customary or imperial system).

Question 3

_______ were historically used in nations once ruled by the British Empire and are still widely used in the United States.

Answer 3

English units (customary or Imperial system)

Question 4

the standard system agreed upon by scientists and mathematicians; and used by virtually every country in the world except United States.

Answer 4

SI units

(part of the metric system)

The acronym “SI” is derived from the French Système International.

Question 5

algebraic combinations of the fundamental units

Answer 5

derived units

Question 6

The fundamental unit of time, the second, is based on ____ clocks.

Answer 6

atomic

An atomic clock uses the vibrations of cesium atoms to keep time to a precision of better than a microsecond per year.

Question 7

In 1983, the meter was given its present definition (partly for greater accuracy) as:

Answer 7

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.

Question 8

_____: the mass of a platinum-iridium cylinder kept with the old meter standard at the International Bureau of Weights and Measures near Paris.

Answer 8

kilogram

Question 9

_____: a system in which values can be calculated in factors of 10

Answer 9

metric system

Question 10

The term ________ refers to the scale of a value expressed in the metric system.

Answer 10

order of magnitude

Question 11

10^1, 10^2, 10^3 are all different ____

Answer 11

orders of magnitude

Question 12

All quantities that can be expressed as a product of a specific power of 10 are said to be of the same _____

Answer 12

order of magnitude

Question 13

_________ 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.

Answer 13

Order of magnitude

Question 14

10^0 =

Answer 14

1

Question 15

10^1 =

Answer 15

10

Question 16

10^3 =

Answer 16

1000

Question 17

10^-1 =

Answer 17

0.1

Question 18

10^-2 =

Answer 18

0.01

Question 19

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.

Answer 19

fundamental unit of seconds

milliseconds

10^-2

Question 20

One cubic centimeter is equal to one milliliter. What does this tell you about the different units in the SI metric system?

Answer 20

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.

Question 21

The four fundamental units are?

Answer 21

1. meter (m)
2. kilogram (kg)
3. second (s)
4. ampere (A)

Question 22

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.

Answer 22

conversion factors

Question 23

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?

Answer 23

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

Question 24

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?

Answer 24

33m x 1km / 1000m = 0.033 km/s

.033 km/s * 3600s = 118.8 km/h

yes it is

Question 25

________: a ratio expressing how many of one unit are equal to another unit

Answer 25

conversion factor