Dust mite size in nanometers micrometers or millimeters

Lesson 2: Scale of Objects

Student Materials

Contents • Visualizing the Nanoscale: Student Reading • Scale Diagram: Dominant Objects, Tools, Models, and Forces at Various

Different Scales

• Number Line/Card Sort Activity: Student Instructions & Worksheet • Cards for Number Line/Card Sort Activity: Objects & Units • Cutting it Down Activity: Student Instructions & Worksheet • Scale of Objects Activity: Student Instructions & Worksheet • Scale of Small Objects: Student Quiz

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Visualizing the Nanoscale: Student Reading How Small is a Nanometer?

The meter (m) is the basic unit of length in the metric system, and a nanometer is one billionth of a meter. It's easy for us to visualize a meter; that’s about 3 feet. But a billionth of that? It’s a scale so different from what we're used to that it's difficult to imagine.

What Are Common Size Units, and Where is the Nanoscale Relative to Them? Table 1 below shows some common size units and their various notations (exponential, number, English) and examples of objects that illustrate about how big each unit is.

Table 1. Common size units and examples.

Unit Magnitude as an exponent (m)

Magnitude as a number (m)

English Expression

About how big?

Meter 100 1 One A bit bigger than a yardstick

Centimeter 10-2 0.01 One Hundredth Width of a fingernail

Millimeter 10-3 0.001 One Thousandth

Thickness of a dime

Micrometer 10-6 0.000001 One Millionth A single cell

Nanometer 10-9 0.000000001 One Billionth 10 hydrogen atoms lined up

Angstrom 10-10 0.0000000001 A large atom

Nanoscience is the study and development of materials and structures in the range of 1 nm (10-9 m) to 100 nanometers (100 x 10-9 = 10-7 m) and the unique properties that arise at that scale. That is small! At the nanoscale, we are manipulating objects that are more than one-millionth the size of the period at the end of this sentence.

What if We Measured the Size of Various Objects in Terms of Nanometers? A typical atom is anywhere from 0.1 to 0.5 nanometers in diameter. DNA molecules are about 2.5 nanometers wide. Most proteins are about 10 nanometers wide, and a typical virus is about 100 nanometers wide. A bacterium is about 1000 nanometers. Human cells, such as red blood cells, are about 10,000 nanometers across. At 100,000 nanometers, the width of a human hair seems gigantic. The head of a pin is about a million nanometers wide. An adult man who is 2 meters tall (6 feet 5 inches) is about 2 billion nanometers tall!

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So is That What Nanoscience is All About––Smallness? No, smallness alone doesn’t account for all the interest in the nanoscale. Nanoscale structures push the envelope of physics, moving into the strange world of quantum mechanics. For nanoparticles, gravity hardly matters due to their small mass. However, the Brownian motion of these particles now becomes important. Nanosized particles of any given substance exhibit different properties and behaviors than larger particles of the same substance. For now, though, we’ll focus just on the smallness of nanoscale, and ways to visualize how extremely tiny the nanoscale is.

How Can We Imagine the Nanoscale? Another way to imagine the nanoscale is to think in terms of relative sizes. Consider yourself with respect to the size of an ant (3-5 millimeters). An ant is roughly 1000 times smaller than you are. Now think of an ant with respect to the size of an amoeba (about 1 micron). An amoeba is about 1000 times smaller than an ant. Now, consider that a nanometer is roughly 1000 time smaller than an amoeba! You would have to shrink yourself down by a factor of 1000 three times in a row in order to get down too the level of the nanoscale.

Imagine Zooming In on Your Hand Let’s try to conceptualize the nanoscale yet another way. Look at your hand. Let’s zoom into your hand by a factor of ten, several times in a row (see Figure 1, below).

In frame 1, at the 10 centimeter scale (10-1 m), we can see fingers and skin clearly. As we zoom in by a factor of ten to the 1 centimeter scale (10-2 m), we can begin to see the structure of skin (frame 2). If we move in another factor of ten to the 1 millimeter scale (10-3 m), we can see cracks in the skin clearly (frame 3). Moving in again by another factor of ten to the 100 micron level (10-4 m), the cracks look like deep crevices (frame 4). Zooming in again, to 10 microns (10-5 m), we can see an individual cell (frame 5). At the next level, 1 micron (10-6 m) we can see the membrane of the cell and some of the features that exist on it (frame 6). Moving in another factor of ten to the 100 nm scale (10-7 m), we begin to see the individual DNA strands that exist within nucleus of the cell. This is the scale at which computer technology is currently being fabricated (frame 7). Zooming in again to the 10 nm length scale (10-8 m), we see the double helix that make up DNA. Finally, zooming in one last time to the 1 nanometer scale (10-9 m), we can see the see individual atoms that make up DNA strands!

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Figure 1. Zooming in on your hand by powers of 10 [1].

What is This Powers of 10 Stuff? In the above example, each picture is an image of something that is 10 times bigger or smaller than the one preceding or following it. The number below each image is the scale of the object in the picture. In the text above, the scale is also written in powers of ten, or exponential notation (e.g., 10-2) where the scale is mentioned. Since the ranges of magnitudes in our universe are immense, exponential notation is a convenient way to write such very large or very small numbers.

The Molecular Expressions Web site offers a nice interactive visualization of magnitudes in our universe; see http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/. The interactive Java applet on this site moves through space in successive orders of magnitude from the Milky Way galaxy (1021 m). our solar system (1013 m). towards the Earth (1018 m), to a city (104 m), a tree (101 m), a leaf (10-1 m), cells (10-5 m), strands if DNA (10-7 m), an atom (10-10 m), and eventually quarks (10-16 m). Check it out!

Another Shrinking Exercise Recall that we said that you’d have to shrink yourself down by a factor of 1000 three times in a row to get to the nanoscale. Let’s try that! [2]

Imagine you are sitting at your desk with the following items: A box, a baseball, a marble, and a grain of salt, as show below. These items represent a length spread of 3 orders of magnitude. Each item is 10 times longer than the item to its left. The box is 1000 times longer than the grain of salt. These objects are in the realm of what is often referred to as the macroscale.

white blood cell skin

DN A

atom s

nanoscale

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10-3 m (1 mm)

10-2 m (1 cm)

10-1 m (10 cm)

1 m

a grain of salt

a marble

a baseball

A box

Figure 2. The macroscale.

What if we zoomed in 1000 times, so that the grain of salt was as big as the box?

• We could stand next to the grain of salt, and use it as a bed or a desk. • Dust mites would look like hand-sized turtles, and your hair would look like giant

ropes.

• Blood cells would be little red and white marbles. • Bacteria on your skin would look like little grains of sand.

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These objects, measured in microns, are in the realm of what is referred to as the microscale.

10-6 m (1 micron)

10-5 m (10 microns)

10-4 m (100 microns)

10-3 m (1 mm)

bacteria

red blood cells

your hair

parasitic mite

a grain of salt

Figure 3. The microscale.

What if we zoomed in 1000 times again, so that the bacteria were as big as the box?

• We could sit on the bacteria like easy chairs. • We could use viruses for batting practice. • We could play marbles with proteins and large molecules. • Atoms and small molecules would look like little grains of sand.

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These objects, measured in nanometers, are in the realm of what is referred to as the nanoscale.

10-9 m (1 nanometer)

10-8 m (10 nanometers)

10-7 m (100 nanometers)

10-6 m (1 micron)

atoms and small molecules

Proteins and large molecules

a virus

bacteria

Figure 4. The nanoscale.

Summary Although many sizes in the universe––including the nanoscale––are hard for us to comprehend because they are far removed from our experience, we can represent such sizes in mathematical notation and through relationships and analogies. Hopefully the examples and analogies used here help you better comprehend the size and scale of the nanoworld.

References (Accessed August 2005.) [1] From M. Hersam’s Introduction to Nanometer Scale Science & Technology at http://www.materialsworld.net/nclt/docs/Introduction%20to%20Nano%201-18-05.pdf [2] Adapted from “A view from the back of the envelope” at http://www.vendian.org/envelope/

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Glossary Term Definition

amoeba A single-celled organism with a nucleus, found in fresh or salt water environments.

bacterium A structurally simple single cell with no nucleus. Bacteria occur naturally almost everywhere on Earth including soil, skin, on plants and many foods.

Brownian motion The random motion of microscopic particles suspended in a liquid or gas, caused by collision with surrounding molecules.

DNA The genetic material of almost every organism. It is a long, double-stranded, helical molecule that contains genetic instructions for growth, development, and replication.

protein An organic compound whose structure is dictated by DNA. Proteins perform a wide variety of functions in the cell including serving as enzymes, structural components, or signaling molecules.

quantum mechanics A scientific model useful for describing the behavior of very small particles (such as atoms and small molecules). Motion is described by probabilistic wave functions and energy can only exist in discrete (quantized) amounts.

quark The basic building block of matter. Quarks combine with gluons to make the protons and neutrons that make up every atom in the universe.

virus A structure containing proteins and nucleic acid. Viruses can infect cells and reproduce only by using their cellular machinery.

wave function A mathematical equation used in quantum mechanics to describe the wave characteristics of a particle. The value of the wave function of a particle at a given point of space and time is related to the likelihood of the particle's being there at the time.

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