Module # 3: Chapters 11-14

11 Compound

A material in which atoms of different elements are chemically bonded to one another.

11 Isotopes

Atoms of the same element that contain different numbers of neutrons.

13.3 Why does buoyant force act upward on an object submerged in water?

Buoyant forces act upward because there is more force beneath an object due to greater pressure at greater depth.

12.2 Which has the greater density: 100 kg of lead or 1000 kg of aluminum?

Density is a ratio of mass to volume (or weight to volume), and this ratio is greater for any amount of lead than for any amount of aluminum

12.2 When water freezes, it expands. What does this say about the density of ice compared with the density of water?

Ice is less dense than water (because it has more volume for the same mass), which is why ice floats on water.

12.3 If a force of 10 N stretches a certain spring 4 cm, how much stretch will occur for an applied force of 15 N?

The spring will stretch 6 cm. By ratio and proportion, (10 N)/(4 cm) = (15 N)/(x cm), which is read: 10 newtons is to 4 centimeters as 15 newtons is to x centimeters; then x = 6 cm. If you are taking a lab, you'll learn that the ratio of force to stretch is called the spring constant, k (in this case, k = 2.5 N/cm), and Hooke's law is expressed as the equation F = kΔx.

11 Atomic mass unit (amu)

The standard unit of atomic mass, which is equal to 1/12 the mass of the most common atom of carbon. One amu has a mass of 1.661 × 10−27 kg.

Surface Tension

The tendency of the surface of a liquid to contract in area and thus to behave like a stretched elastic membrane.

13.4 If a 1-L container is immersed halfway into water, what is the volume of the water displaced? What is the buoyant force on the container?

The volume that is displaced is 1/2 L.

Which is more likely to hurt: being stepped on by a 200-lb man wearing loafers or being stepped on by a 100-lb woman wearing high heels?

The woman stepping on you would hurt more because there is less area of contact in which all of the weight is distributed upon.

How many individual atoms are in a water molecule?

There are 3 atoms in H2O, 2 Hydrogen and 1 Oxygen.

14.4 Is there a buoyant force acting on you? If there is, why aren't you buoyed up by this force?

There is a buoyant force acting on you, and you are buoyed upward by it. You don't notice it only because your weight is so much greater.

11.5 How many shells are represented in the presently known periodic table?

There is a maximum of 7 shells.

Why are persons who are confined to bed less likely to develop bedsores on their bodies if they rest on a waterbed rather than on an ordinary mattress?

There is less pressure with the waterbed due to the larger contact area.

11.8 How many atomic nuclei are in a single oxygen atom? In a single oxygen molecule?

There is one nucleus in an oxygen atom, O, and two in the combination of two oxygen atoms—an oxygen molecule, O2.

11.5 Why aren't heavier elements much larger than lighter elements?

They are not much larger due to the electrical attraction by greater charge in the nucleus.

13.5 What is the condition in which the buoyant force on an object does equal the weight of the object?

When an object floats, its buoyant force equals its weight.

11.9 What occurs when a particle of matter and a particle of antimatter meet?

When matter meets antimatter, equal masses of each annihilate.

A 12-kg piece of metal displaces 2 L of water when submerged. Show that its density is 6000 kg/m3. How does this compare with the density of water?

m 12 kg Density = ---- = ------ = 6kg/L v 2L

11 Antimatter

A "complementary" form of matter composed of atoms that have negative nuclei and positive electrons.

12.3 A 2-kg antique painting is hung from the end of a spring. The spring stretches a distance of 10 cm. If, instead, a 4-kg painting is hung from the same spring, how much will the spring stretch? If a 6-kg painting is hung from the same spring? (Assume that none of these loads stretches the spring beyond its elastic limit.)

A 4-kg load (painting in this case) has twice the weight of a 2-kg load. In accord with Hooke's law, F ∼ Δx, 2 times the applied force results in 2 times the stretch, so the spring stretches 20 cm. The weight of the 6-kg load makes the spring stretch 3 times as far, 30 cm. (If the elastic limit were exceeded, the amount of stretch could not be predicted with the information given.)

14.1 Why do your ears sometimes pop when you change altitude—say, moving in a skyscraper elevator or descending in an airplane?

A change in altitude means a change in air pressure, as discussed in the next section, and this causes a temporary imbalance in the pressures on the two sides of your eardrum.

11 Periodic table of the elements

A chart that lists the elements in horizontal rows by their atomic number and in vertical columns by their similar electron arrangements and chemical properties.

Barometer

A device that measures atmospheric pressure.

Principle of Flotation

A floating object displaces a weight of fluid equal to its own weight.

11 Electron

A negatively charged particle that whizzes about within an atom.

11 Proton

A positively charged particle in the nucleus of an atom.

11 Element

A pure substance that consists of only one kind of atom.

13.8 What geometrical shape has the smallest surface area for a given volume?

A sphere.

13.4 Distinguish between an immersed and a submerged body.

A submerged body is completely immersed, totally beneath the surface.

11 Mixture

A substance whose components are mixed together without combining chemically.

13.9 Distinguish between adhesive and cohesive forces.

Adhesion is the attraction between unlike substances; cohesion is the attraction between like substances.

11.1 Who first explained Brownian motion and made a convincing case for the existence of atoms?

Albert Einstein explained Brownian motion

11 Ion

An electrically charged atom; an atom with an excess or deficiency of electrons.

11 Neutron

An electrically neutral particle in the nucleus of an atom.

Archimedes' principle

An immersed body is buoyed up by a force equal to the weight of the fluid it displaces.

About how many kilograms of air occupy a classroom that has a 200-m2 floor area and a 4-m-high ceiling? (Assume a chilly temperature of 10°C.)

At normal classroom temperature the mass of air is 1000 kg. The volume of air is area × height = 200 m2 × 4 m = 800 m3; each cubic meter of air has a mass of about 1.25 kg, so 800 m3 × 1.25 kg/m3 = 1000 kg.

14.2 What is the maximum height to which water can be sucked up through a straw?

At sea level, however strong your lungs may be, or whatever device you use to make a vacuum in the straw, the water cannot be pushed up by the atmosphere higher than 10.3 m.

A scuba diver 10.3 m deep breathes compressed air. If she holds her breath while returning to the surface, by how much will the volume of her lungs tend to increase?

Atmospheric pressure can support a column of water 10.3 m high, so the pressure in water due to its weight alone equals atmospheric pressure at a depth of 10.3 m. If we take the pressure of the atmosphere at the water's surface into account, the total pressure at this depth is twice atmospheric pressure. Unfortunately for the scuba diver, her lungs will tend to inflate to twice their normal size if she holds her breath while rising to the surface. A first lesson in scuba diving is not to hold your breath when ascending. To do so can be fatal.

Why doesn't the pressure of the atmosphere break windows?

Atmospheric pressure is exerted on both sides of a window, so no net force is exerted on the glass. If, for some reason, the pressure is reduced or increased on one side only, as when a tornado passes by, then watch out! Reduced outside air pressure created by a tornado can be disastrous.

11.3 Why can atoms be seen with an electron beam?

Atoms are larger than the wavelength of an electron beam.

13.3 How does the volume of a completely submerged object compare with the volume of water displaced?

Both volumes are the same.

What is the cause of the Brownian motion of dust and other small particles? Why aren't larger objects, such as baseballs, similarly affected?

Brownian motion is caused by more atoms or molecules bumping against one side of a tiny particle than the other This produces a net force on the particle, which alters motion. Such Brownian motion is not observed for larger particles because the number of bumps on opposite sides is more nearly equal, and the inertia of the larger particle is greater. Any Brownian motion on the baseball would be impermeable. The number of bumps on the baseball are practically the same with no net force and no change on the baseball's motion.

12.2 Which weighs more: a liter of ice or a liter of water?

Don't say that they weigh the same! A liter of water weighs more. If it is frozen, then its volume will be more than a liter. If you shave the extra part off so that the chunk of ice is the same size as the original liter of water, it will certainly weigh less.

12.4 Suppose you drill a hole horizontally through a tree branch as shown. Where will the hole weaken the branch the least: through the upper portion, the middle portion, or the lower portion of the branch?

Drill the hole horizontally through the middle of the branch, through the neutral layer—a hole at that location will hardly affect the branch's strength because fibers there are neither stretched nor compressed. Wood fibers in the top part are being stretched, so drilling a hole there may result in fibers pulling apart. Fibers in the lower part are compressed, so drilling a hole there might crush under compression.

Calculate the average force per nail when Sara, who weighs 120 pounds, lies on a bed of nails and is supported by 600 nails

Force per nail is 120 pounds/600 nails = 0.2 pounds per nail, quite tolerable.

11.4 How are elements with nuclei heavier than those of hydrogen and helium formed?

Heavier atoms are formed by fusion inn star interiors.

13.6 A river barge loaded with gravel approaches a low bridge that it cannot quite pass under. Should gravel be removed from or added to the barge?

Ho, ho, ho! Do you think ol' Hewitt is going to give all the answers to Check Point questions? Good teaching is asking good questions, not providing all the answers. You're on your own with this one!

11.4 What element has the lightest atoms?

Hydrogen has the lightest atoms.

14.4 (This one calls for your best thinking!) How does buoyancy change as a helium-filled balloon ascends?

If the balloon is free to expand as it rises, the increase in volume is counteracted by a decrease in the density of higher-altitude air. So, interestingly, the greater volume of displaced air doesn't weigh more, and buoyancy stays the same. If a balloon is not free to expand, buoyancy will decrease as a balloon rises because of the less-dense displaced air. Usually, balloons expand as they rise initially, and, if they don't finally rupture, the stretching of their fabric reaches a maximum, and they settle where their buoyancy matches their weight. As Figure 14.15 shows, high-altitude balloons appear very under-inflated at launch.

13.7 What happens to the pressure in all parts of a confined fluid if the pressure in one part is increased?

If the pressure in one part is increased, the same increase in pressure is transmitted to all parts.

11.1 Who advanced the idea of atoms in the early 1800s?

John Dalton advanced the idea of the atom.

13.2 What is the relationship between liquid pressure and the depth of a liquid? Between liquid pressure and weight density?

Liquid pressure is proportional to depth and to weight density.

11.1 Are most of the atoms around us younger or older than the Sun?

Most of them are older than the Sun.

11.4 Where in the atom is most of its mass concentrated?

Nearly all the mass of an atom is concentrated in the nucleus.

If a friend commented that a hydraulic device is a common way of multiplying energy, what would you say?

No, no, no! Although a hydraulic device, like a mechanical lever, can multiply force, it always does so at the expense of distance. Energy is the product of force and distance. If you increase one, you decrease the other. No device has ever been found that can multiply energy!

13.6 It was emphasized earlier that the buoyant force does not equal an object's weight but does equal the weight of the displaced water. Now we say that the buoyant force equals the object's weight. Isn't this a grand contradiction? Explain.

No. In the case of floating, the buoyant force equals both the weight of the object and the weight of the water displaced.

A 1-m-tall barrel is filled with water (with a weight density of 10,000 N/m3). Show that the water pressure on the bottom of the barrel is 10,000 N/m2 or, equivalently, 10 kPa.

Pressure = (weight density)(depth) = (10,000 N/m^3)(1m) = 10,000 m^2 = 10kpa

The depth of water behind the Hoover Dam is 220 m. Show that the water pressure at the base of this dam is 2200 kPa.

Pressure = (weight density)(depth) = (10,000N/m^3)(220m) = 2,200,00 N/m^2 = 2,200 kpa

13.1 How does pressure relate to force?

Pressure is force per area. or Pressure= (force)(area)

11.6 Which contributes more to an atom's mass: electrons or protons? Which contributes more to an atom's volume (its size)?

Protons contribute more to an atom's mass; electrons contribute more to its size.

A recipe calls for a specific amount of butter. How does the displacement method relate to the use of a kitchen measuring cup?

Put some water in the cup before you add the butter. Note the water-level reading on the side of the cup. Then add the butter and you'll note the water level rise. Because butter floats, poke it beneath the surface. When you subtract the lower-level reading from the higher-level reading, you know not only the volume of water displaced but also the volume of the butter.

11.2 Are there really atoms that were once a part of Albert Einstein incorporated in the brains of all the members of your family?

Quite so, and of Barack Obama too. However, these atoms are combined differently than they were previously. If you experience one of those days when you feel like you'll never amount to anything, take comfort in the thought that many of the atoms that now constitute your body will live forever in the bodies of all the people on Earth who are yet to be. Our atoms are immortal.

11.8 Is common table salt an element, a compound, or a mixture?

Salt is not an element; if it were, you'd see it listed in the periodic table. Pure table salt is a compound of the elements sodium and chlorine, represented in Figure 11.14. Notice that the sodium atoms (green) and the chlorine atoms (yellow) are arranged in a 3-dimensional repeating pattern—a crystal. Each sodium atom is surrounded by six chlorine atoms, and each chlorine atom is surrounded by six sodium atoms. Interestingly, there are no separate sodium-chlorine groups that can be labeled molecules.3

In a gaseous mixture of hydrogen and oxygen gas, both with the same average kinetic energy, which molecules move faster on average?

The Hydrogen atoms move faster because the lighter ones move faster and the heavier ones move slower than the lighter ones.

11.2 Which are older: the atoms in the body of an elderly person or those in the body of a baby?

The age of the atoms in both is the same. Most of the atoms were manufactured in stars that exploded before the solar system came into existence.

In what sense can you truthfully say that you are a part of every person in history? In what sense can you say that you will tangibly contribute to every person on Earth who will follow?

The atoms are not created nor destroyed. They are conserved and transformed from form to form.

A 1-L container completely filled with lead has a mass of 11.3 kg and is submerged in water. What is the buoyant force acting on it?

The buoyant force equals the weight of the liter of water displaced—not the weight of the lead! One L of water has a mass of 1 kg and weighs 10 N. So the buoyant force on it is 10 N.

13.5 Two solid blocks of identical size are submerged in water. One block is lead and the other is aluminum. Upon which is the buoyant force greater?

The buoyant force is the same on both blocks because they displace the same volume of water. For submerged objects, the buoyant force is determined by only the volume of water displaced, not the object's weight.

As a boulder thrown into a deep lake sinks deeper and deeper into the water, does the buoyant force on it increase or decrease?

The buoyant force remains unchanged as the boulder sinks because the boulder displaces the same volume and the same weight of water at any depth.

11 Atomic nucleus

The core of an atom, consisting of two basic subatomic particles—protons and neutrons.

12.2 What is the density of 1000 kg of water?

The density of any amount of water is 1000 kg/m3 (or 1 g/cm3).

11.5 What fundamental force dictates the size of an atom?

The electrical force.

11.8 Compared with the energy it takes to separate oxygen and hydrogen from water, how much energy is released when they recombine?

The energy is the same: Energy of separation equals energy of recombination.

11.2 The world's population grows each year. Does this mean that the mass of Earth increases each year?

The greater number of people increases the mass of Earth by zero. The atoms that make up our bodies are the same atoms that were here before we were born—we are but dust, and unto dust we shall return. The materials that make up human cells are rearrangements of material already present. The atoms that make up a baby forming in its mother's womb are supplied by the food the mother eats. And those atoms originated in stars—some of them in faraway galaxies. (Interestingly, the mass of Earth does increase by the incidence of roughly 40,000 tons of interplanetary dust each year, but not by the birth and survival of more people.)

11 Brownian motion

The haphazard movement of tiny particles suspended in a gas or liquid that results from their bombardment by the fast-moving atoms or molecules of the gas or liquid.

11.6 Which is represented by a whole number: the mass number or the atomic mass?

The mass number is always given as a whole number, such as hydrogen- 1 or carbon-12. Atomic mass, by contrast, is the average mass of the various isotopes of an element and is thus represented by a fractional number.

Buoyant force

The net upward force that a fluid exerts on an immersed object.

12.4 When you walk on floorboards in an old house that sag due to your weight, where is the neutral layer?

The neutral layer is midway between the top and bottom surfaces of the floorboards.

11 Atomic number

The number that designates the identity of an element, which is the number of protons in the nucleus of an atom; in a neutral atom, the atomic number is also the number of electrons in the atom.

Helium is an inert gas, which means that it doesn't readily combine with other elements. What five other elements would you also expect to be inert gases? (See the periodic table.)

The others are noble gases. Neon, Xenon, Argon, Krypton, and Radon.

Pascal's Principle

The pressure applied to a motionless fluid confined in a container is transmitted undiminished throughout the fluid.

Atmospheric pressure

The pressure exerted against bodies immersed in the atmosphere. It results from the weight of air pressing down from above. At sea level, atmospheric pressure is about 101 kPa.

14.3 A piston in an airtight pump is withdrawn so that the volume of the air chamber is increased three times. What is the change in pressure?

The pressure in the piston chamber is reduced to one-third. This is the principle that underlies a mechanical vacuum pump.

13.2 How does the water pressure 1 m below the surface of a small pond compare with the water pressure 1 m below the surface of a huge lake?

The pressures are the same at the same depth.

Which contributes more to an atom's mass: electrons or protons? Which contributes more to an atom's size?

The protons contribute to the elements mass and the electrons contribute to the elements size

Pressure

The ratio of force to the area over which that force is distributed: Pressure= (force)(area) Liquid pressure = weight density × depth

Capillary

The rise of a liquid in a fine, hollow tube or in a narrow space.

11 Atom

The smallest particle of an element that has all of the element's chemical properties.

11.6 Do the two isotopes of iron have the same atomic number? The same atomic mass number?

The two isotopes of iron have the same atomic number 26 because they each have 26 protons in the nucleus. They have different atomic mass numbers if they have different numbers of neutrons in the nucleus.

12.2 What is the volume of 1000 kg of water?

The volume of 1000 kg of water is 1 m3.

12.5 Why is it easier for a chick inside an eggshell to poke its way out than it is for a chicken on the outside to poke its way in?

To poke its way into a shell, a chicken on the outside must contend with compression, which greatly resists shell breakage. But, when a chick pokes from the inside, only the weaker shell tension must be overcome. To see that the compression of the shell requires greater force, try crushing an egg along its long axis by squeezing it between your thumb and fingers. Surprised? Try it along its shorter diameter. Surprised? (Do this experiment over a sink with some protection, such as gloves, for possible shell splinters.)

True or false? Archimedes' principle tells us that any object that displaces 10 N of liquid will be buoyed up with 10 N.

True. It's only the weight of the displaced liquid that counts. (Also look at it in a Newton's third law way: If the immersed object pushes 10 N of fluid aside, the displaced fluid reacts by pushing back on the immersed object with 10 N.)

11 Molecule

Two or more atoms that bond together by a sharing of electrons. Atoms combine to become molecules.

Dark matter

Unseen and unidentified matter that is evidenced by its gravitational pull on stars in the galaxies. Dark matter along with dark energy constitutes perhaps 96% of the stuff of the universe.

13.5 If a fish makes itself denser, it will sink; if it makes itself less dense, it will rise. In terms of the buoyant force, why is this so?

When the fish makes itself more dense by decreasing its volume, it displaces less water, so the buoyant force decreases. When the fish makes itself less dense by expanding its volume, more water is displaced and the buoyant force increases.

13.2 Suppose that you raise one foot when you are standing on a bathroom scale. Does the pressure you exert on the scale change? Is there a difference in the scale reading?

When you shift your weight by standing on one foot, the pressure on the scale's surface doubles. But the scale doesn't measure pressure—it measures weight. Except for some jiggling as you shift your weight, the scale reading stays the same.

A dike in Holland springs a leak through a hole of area 1 cm2 at a depth of 2 m below the water surface. How much force must a boy apply to the hole with his thumb to stop the leak? Could he do it?

Yes. First find the pressure. it is (weight density)(depth) = (10,000 N/m^3)(2m) = 20,000 N/m^3, or 20,000 Pa. Force is (pressure)(area), and 1cm^2 = 10^-4 m^2, so F=(20,000 N/m^2)(10^-4m^2) = 2N. It would be easy for this boy to exert this force. It is about the weight of a notebook or a small box of cereal. (Air pressure is not taken into account.)

12.6 If you were somehow scaled up to twice your size while retaining your present proportions, would you be stronger or weaker? Explain your reasoning.

Your scaled-up self would be 4 times as strong because the cross-sectional area of your twice-as-thick bones and muscles would increase by 4. You could lift a load 4 times as heavy. But your weight would be 8 times greater than before, so you would not be stronger relative to your greater weight. You would have 4 times the strength but carry 8 times the weight, which gives you a strength-to-weight ratio only half its former value. So, if you can barely lift your own weight now, when scaled up you could lift only half your new weight. Your strength would increase, but your strength-to-weight ratio would decrease. Stay as you are!

Consider the following atoms: A. gold, B. copper, C. carbon, and D. silver. Consult the periodic table and rank these atoms, from most to least, by their a.) Mass b.) Number of electrons c.) Number of protons

a.) A,D,B,C b.) A,D,B,C c.)A,B,D,C