Physics in the Natural World

This course (designed for grades 11 or 12) builds on the content learned in the ninth-grade Physical and Earth Science course by offering inquiries and explorations designed to help students develop conceptually coherent models of observable and unobservable physical phenomena. Throughout the course, emphasis is placed on mathematical modeling of the physical world.

Within the course, there are 12 quests from which to develop standards-based learning cycle lessons:

1. Quest 1: Motion and Forces
2. Quest 2: Work
3. Quest 3: Space
4. Quest 4: Matter
5. Quest 5: Heat
6. Quest 6: Waves
7. Quest 7: Sound Waves
8. Quest 8: Light Waves
9. Quest 9: Electricity
10. Quest 10: Magnetism
11. Quest 11: Quantum Mechanics
12. Quest 12: Nuclear Energy

Quest 1: Motion and Forces

• The motion of an object can only be described in relation to a defined frame of reference. Using this frame of reference, a change in an object’s position is then described in terms of velocity, which has both a magnitude and a direction. Acceleration is the rate of change of velocity.
• Newton’s three laws of motion are the cornerstone in explaining the interaction of objects. Newton’s first law of motion states that a body in motion will remain in motion at a constant speed and direction unless an outside unbalanced force acts upon it. Likewise, if the body is at rest and no outside unbalanced force acts upon it, it will remain at rest.
• Newton’s second law of motion explains that the net force acting upon an object is directly related to the mass and acceleration of the object. The resulting acceleration is in the direction of the net force, which is the vector sum of all forces acting upon the object (including friction).
• Newton’s third law of motion explains that forces come in pairs—when one object applies a force to another, the other object applies the same amount of force back to the first object, but in the opposite direction.

Examples of Essential Questions for Investigation:

1. How has our understanding of motion and forces made such games as football, hockey, and baseball safer?
2. How can physics be used to describe the motion of earthquakes, hurricanes, and tornadoes?

Quest 2: Work

• The law of conservation of energy explains that energy is not created or destroyed but changes forms. The total amount of energy stays the same. Work adds or subtracts energy from a system. Within the system, energy can change form without work being done.
• Objects have kinetic energy whenever they are in motion according to the formula KE = ½ mv2 (m = mass, v = velocity). An object has gravitational potential energy if it is raised above a height (defined as “0”) according to the formula PE = mgh (m = mass, g = gravitational acceleration constant, h = height above “0”). Work must be done on the object for the object’s energy to change from one form of energy to another.
• The energy of an object may be converted into one or more forms of energy (e.g., heat, light, sound). Often this energy is much less useful than other forms to do work.
• The impulse momentum change theorem is a rearrangement of Newton’s second law of motion. This theorem states that the impulse acting upon an object is equal to the change in momentum of the object. This is summarized in the following formula:
  FΔt = mΔv
  Impulse = Change in Momentum
  (F = force, Δt = change in time, m = mass, and Δv = change in velocity)
• Circular motion can be described in terms of centripetal acceleration and centripetal force. Gravity, tension, and electromagnetic forces hold objects in a circular path of motion. Throughout this circular path, the net force (or centripetal force) is directed toward the center of rotation. This causes a change in the direction of the velocity of the object. This change in velocity results in centripetal acceleration, which also is directed toward the center of the circular path. An example of this is the gravitational pull of the sun keeping the Earth in its somewhat circular path.

Examples of Essential Questions for Investigation:

1. How does a NASCAR driver survive a crash at 150 mph?
2. What are the principles behind high-speed safety devices such as airbags, seat belts, and collision barriers?

Quest 3: Space

• In the late-1500s and early-1600s, Johannes Kepler explained the motion of planets around the sun and satellites around planets with his three laws of planetary motion. These laws represented a big move away from the belief of an Earth-centered universe.
• In the mid-1600s, Isaac Newton developed his law of universal gravitation that mathematically explained that a force of attraction exists between any two objects in the universe. This force is proportional to the masses of the objects and inversely proportional to the square of the distance between the two objects.
• In the early-1900s, Albert Einstein realized that Isaac Newton’s law of universal gravitation possessed some shortcomings, including the notion of “action at a distance.” To replace Newton’s theory, Einstein developed the theory of general relativity, which explains that mass causes space to curve and that the curvature of space determines how mass and light move through it. Space then is replaced with the concept of space–time, since space and time are different aspects of the same fabric.
• General relativity explains the existence of black holes and the beginning of all matter, energy, space, and time—lending support to the big bang theory.

Examples of Essential Questions for Investigation:

1. GPS systems rely on satellites orbiting the Earth. How does this work?
2. How does rotational mechanics explain the shape of galaxies?
3. What physics concepts must NASA consider when sending a probe into the vast reaches of our solar system?
4. How does Einstein’s work contribute to the historical development of our scientific knowledge of space?

Quest 4: Matter

• Every substance has unique chemical and physical properties. Chemical properties can only be tested when the substance undergoes a chemical reaction. Physical properties can be tested without changing the chemical make up of the substance. Physical properties of substances can be used to explain many phenomena we see in everyday life.
• All fluids (liquids and gases) exert pressure on the surfaces of containers in which they reside. This can be represented by the following formula P = F/A (P = pressure, F = force, and A = area). The force and the area are always perpendicular to each other. In the late-1600s, Blaise Pascal took this idea one step further to say that any pressure applied to a confined fluid is transmitted, undiminished in all directions throughout the fluid.
• In 212 B.C., Archimedes discovered that an object that is completely or even partially immersed in a fluid has an upward force acting on it that is equal to the weight of the fluid displaced by the object. This idea helps explain why very massive objects (e.g., aircraft carriers, luxury liners) can float.
• Daniel Bernoulli’s principle of moving fluids developed in the mid-1700s explains that as the velocity of a fluid increases, the pressure exerted by that fluid decreases. This principle explains the lifting ability of air as it flows over curved airplane wings.
• Molecules in a real liquid exert attractive forces on each other. In the case of water, these attractive forces between the water molecules result in surface tension. This can be observed when water forms into droplets.
• Thermal expansion explains why most solids and liquids will expand when heated. This idea of thermal expansion is critical when designing materials that must perform at a variety of temperatures.

Examples of Essential Questions for Investigation:

1. How do the properties of fluids influence airplane design and flight?
2. How must thermal expansion be considered in designing bridges and overpasses?

Quest 5: Heat

• Heat is the energy that flows between two objects as a result of a difference in their temperatures. Temperature is a measurement of the average kinetic energy of the particles that make up a substance.
• The Celsius temperature scale is based on the freezing and boiling temperatures of water. Zero degrees Celsius is the freezing point of pure water at standard pressure, and 100oC is the boiling point of pure water at standard pressure. The Kelvin scale uses absolute zero (the temperature at which all molecules lack translational kinetic energy) as the zero of its scale. Zero kelvin is equivalent to -273.15oC. Each degree has the same magnitude on both scales.
• Heat travels from warm objects to cool objects. Three ways this thermal energy can transfer are conduction, convection and radiation. Conduction occurs when two objects in direct contact with one another are at different temperatures. Convection occurs in fluids where currents are set up within the fluid and warm fluids rise and cooler fluids sink. Radiation is the process by which thermal energy is transferred through a vacuum (e.g., radiant energy from the sun warms us on Earth).
• All materials have unique specific heat capacity values. These values represent the amount of heat energy needed to raise one kilogram of the substance one kelvin. The greater this value, the more energy that must be added per unit mass to raise the temperature one kelvin. This is an important concept in explaining why large bodies of water maintain fairly constant temperatures.
• A temperature-versus-time graph can be used to explain the change of state of a substance as it changes from a solid (melting point), to a liquid, and then to a gas (boiling point). The temperatures at which the object changes from a solid to a liquid and from a liquid to a gas are indicated by the plateaus that occur on this graph.
• The first law of thermodynamics explains that the thermal energy of a system can be increased by doing work on the system or adding heat to the system. The second law of thermodynamics states that all processes tend to progress in the direction that allows the entropy of the universe to increase.

Examples of Essential Questions for Investigation:

1. How have materials used in the design of homes changed in the last 200 years to minimize heat transfer?
2. Why are temperatures moderate near the coast of large bodies of water (e.g., the Pacific Ocean and its impact on the city of San Diego)?
3. How are humans and other animals able to live in areas of the Earth with very wide temperature extremes?

Quest 6: Waves

• Transverse waves vibrate perpendicularly to the direction of wave motion. Longitudinal (or compressional) waves vibrate in the same direction as the wave’s motion. All waves on the electromagnetic spectrum are examples of transverse waves; sound waves are examples of longitudinal waves.
• All waves can be described in terms of certain physical properties. Amplitude is the maximum height of a wave as measured from its equilibrium position. Amplitude indicates brightness in a light wave and loudness in a sound wave. A crest is the high point of a wave and a trough is the low point of a wave. The distance from one point on a wave to its corresponding point on the next wave is known as one wavelength.
• The number of waves that pass by per second is the frequency of the wave. The period of a wave is the time needed for one wave to pass. The frequency and period are inverses of each other.
• Superposition of waves explains what happens to the amplitude of the wave that forms as two waves occupy the same space at the same time. Waves can either constructively or destructively interfere with each other.
• Reflection occurs when a wave bounces off a boundary between different materials. When reflection occurs to sound waves, an echo is produced. When waves change direction as they pass through the boundary between two different media we say refraction has occurred. Diffraction occurs as a wave bends around an obstacle or passes through an opening.

Examples of Essential Questions for Investigation:

1. Why do military troops “break step” (march out-of-step) when crossing a bridge?
2. What caused the Tacoma Narrows suspension bridge to collapse in 1940?
3. What is the chance of an earthquake striking your area of Ohio, and what type of waves would be involved?

Quest 7: Sound Waves

• Sound waves are mechanical waves that have the ability to bounce or reflect off of rigid objects. This is how echoes are produced.
• If sound waves are provided an opportunity to continually reflect back upon themselves (as they might along a tight string or in an air tube), standing waves may be produced. The frequency (or pitch) of these waves can be controlled by changing their wavelengths. The various wavelengths that can be produced are known as harmonics.
• The intensity of sound is related to the amplitude of its wave. Resonance increases the amplitude of waves. Resonance occurs when an externally produced vibration matches an object’s natural frequency.
• The Doppler effect explains how the perceived pitch (frequency) of a sound changes as the object producing the sound moves toward or away from an observer, or as the observer moves toward or away from the source. As the source moves away from the observer (or the observer moves away from the source), the wavelength increases. This increase causes a decrease in frequency; therefore, the pitch becomes lower. Conversely, if the source moves toward the observer (or the observer moves toward the source) the wavelength decreases. This decrease causes an increase in frequency; therefore, the pitch becomes higher.

Examples of Essential Questions for Investigation:

1. How is sound produced in an instrument? How does it then travel to our ears?
2. Why was it so difficult for airplanes to break the sound barrier?
3. Why does sound of the same frequency sound different when produced by different instruments?

Quest 8: Light Waves

• Light waves are transverse waves.
• Light reflects off a multitude of surfaces, including plane mirrors. The angle of incidence of the light beam onto a plane mirror is equal to the angle of reflection of the light as it bounces off the plane mirror. This rule, known as the law of reflection, always holds true.
• Light bends as it passes from one medium to another. Snell’s law can be used to predict the amount the light ray will bend (refract) as it travels into the second medium. If light travels to another medium that is less optically dense, it may bend so far that none of the light refracts into the new material. This is known as total internal reflection.
• Real images are formed at the convergence of light rays. These images can be focused on a screen or piece of paper. Virtual images cannot be focused on a screen because light rays do not converge where these images are formed. Plane and convex mirrors and concave lenses form only virtual images. Concave mirrors and convex lenses can form both virtual and real images, depending on the location of the object in relation to the focal point of the mirror.
• Image locations and heights can be found by creating ray diagrams, using the lens/mirror equation (1/f = 1/di + 1/do, where f = focal length, di = image distance, and do = object distance), and also using the magnification equation (m = hi/ho = - di/do, where hi = image height, ho = object height, di = image distance, and do = object distance)

Examples of Essential Questions for Investigation:

1. 1. How do glasses, contact lenses, and laser surgery correct our vision?
2. What actually happens to light waves as they travel from one substance into another or as they bounce off an object?

Quest 9: Electricity

• Two charges exist in nature—positive and negative. Only negative charges (electrons) are free to move. Electrons can move freely through conductors, but not through insulators.
• An object can be given a charge by induction or conduction. If a neutral body is touched with a charged body, electrons will flow from one object to the other to balance out the overall charge. When the initial charged body is removed, the initially neutral body is left with a charge; this is charging by conduction (or by contact). When a charged body is brought near (but does not touch) a neutral body, this will cause electrons to migrate in the neutral body; this is charging by induction.
• Electric charge is measured in coulombs. One coulomb is the charge on a very large number of electrons (6.25 × 1018 electrons). Charles Coulomb found that the force between any two charged objects is directly related to their charge and inversely related to the square of the distance between them.
• All charged objects have a surrounding electric field. We can measure the strength of this electric field by measuring what happens to a small positive test-charge when it is placed within this electric field.
• Electrical potential difference can be measured using a test-charge in an electric field. This is a measurement of the work that would need to be done on the test-charge divided by the magnitude of the charge required to move the test-charge within the electric field. A good analogy for this is how an object’s gravitational potential energy can be changed by raising or lowering an object in Earth’s gravitational field.
• All circuits need a power supply, a closed pathway for electrons to travel, and a resistance or load.
• Ohm’s law (R = V/I ) explains the relationships among electric current (I), potential difference (voltage = V), and resistance (R) of a conductor.
• Series circuits provide only one possible path for the current. Parallel circuits provide multiple paths. The sum of the voltage drops across resistors in a series circuit equals the voltage of the source. The same current flows through all resistors in a series circuit. Current splits over different branches of a parallel circuit; and each branch of a parallel circuit experiences the same voltage drop.

Examples of Essential Questions for Investigation:

1. How do designers of very small electronics handle and manage the magnetic fields formed around the components of these small electric circuits?
2. What are the advantages and disadvantages of using AC instead of DC current (e.g., electricity production, electricity transmission, effect on appliances)?

Quest 10: Magnetism

• All magnets have two distinct ends—a north-seeking end and a south-seeking end. Magnetism is explained with a model that states that many domains (groups of neighboring electrons) are aligned in the same direction in a magnet. A magnetic field exists around all permanent magnets. This field is strongest around the poles.
• Magnetic fields exist around any current-carrying wire or loop of wire. Current- carrying wires placed in magnetic fields may actually jump because of the force of the magnetic field. A loop of wire moving within a magnetic field will generate a current. Electromagnetism is the relationship between electricity and magnetism.
• One right-hand-rule can be used to determine the relationships among a moving charge in a magnetic field, the direction of the field, and the force on the charge. Other right-hand-rules can be used to determine the direction of magnetic fields around wires.
• A generator produces an electric current by allowing loops of wire to turn freely within a magnetic field. The more loops that are in the wire, the quicker the wire spins; or, the stronger the magnetic field, the greater the EMF (electromotive force, or potential difference) induced within the wire. A motor then uses this electrical energy to perform work.
• Modern technology is progressing at a rapid rate. The use of microchips (miniaturized integrated circuits) has allowed designers to build electronics faster, smaller, and more reliably.

Examples of Essential Questions for Investigation:

1. How do motors, machines, and appliances combine magnetism and electricity to make various objects work?
2. What are the implications for our communications and navigation systems when the Earth’s magnetic poles flip?

Quest 11: Quantum Mechanics

• Quantum mechanics attempts to explain the properties of matter by studying its wave and particle properties. Objects absorb (absorption spectra) and emit (emission spectra) very specific amounts and types of radiation. These discrete amounts of energy are called photons. This theory tries to show that light has a dual nature—that of a particle and a wave.
• The photoelectric effect occurs when electrons are emitted from a piece of metal struck by radiation of a certain frequency or higher. Quantum mechanics can explain this phenomenon, but the wave theory cannot.
• Particles such as electrons and protons exhibit properties of waves (such as interference and diffraction).

Examples of Essential Questions for Investigation:

1. How does the theory that atoms can only gain or lose discrete amounts of energy affect everything we see around us?
2. How has the development of our understanding of quantum mechanics aided in our understanding of the age and composition of the universe?
3. How have Planck, Einstein, de Broglie, and Compton contributed to the field of quantum mechanics?

Quest 12: Nuclear Energy

• The majority of the mass of an atom is contained in its nucleus. This nucleus contains both protons (positively charged particles) and neutrons (neutral particles). Electrons (negatively charged particles) are found outside the nucleus. The atomic number of an element is the number of protons in its nucleus; this number is what makes an element unique. The atomic mass is the sum of the protons and neutrons in the nucleus of an atom. Isotopes of an element contain the same number of protons but different numbers of neutrons. If an isotope contains too many neutrons, it becomes unstable and is ripe for nuclear decay.
• The elementary particles that make up protons, neutrons and electrons are divided into three main categories—quarks, leptons, and force carriers.
• There are three types of nuclear decay—alpha, beta, and gamma. Alpha decay involves the emission of an alpha particle (two protons and two neutrons) from the nucleus of the atom. Beta decay involves the release of high-speed electrons and antineutrinos from the nucleus of an atom—thus converting a neutron into a proton. Gamma decay involves the release of high-energy photons from the nucleus.
• The half-life of a radioactive isotope is the time required for one-half of the atoms in the substance to decay from its unstable nucleus to produce a more stable nucleus. Half-lives range from fractions of a second to billions of years. Half-lives allow us to determine the age of objects. For example, carbon dating allows us to determine the age of organic artifacts and uranium dating allows us to determine the age of rocks and geologic formations.
• Nuclear reactions can be described in equations similar to chemical equations.
• Albert Einstein postulated the relationship between matter and energy in the equation E = mc2, where E is energy; m is mass, and c is the speed of light. This equation explains the basis of nuclear energy.
• Fission may occur when a nucleus is bombarded with neutrons. This causes the nucleus to split and release more neutrons, which in turn bombard other nuclei. This bombardment, in turn, can result in a chain reaction—releasing large amounts of energy. This process is the basis for nuclear reactors and nuclear weapons.
• Fusion occurs when small nuclei combine to form a nucleus with larger mass, releasing large amounts of energy. This process is occurring in the sun. Controlled fusion reactions are currently being researched as possible energy sources.

Examples of Essential Questions for Investigation:

1. Is radon a problem in Ohio? If not, why not? If so, what are homeowners advised to do about it?
2. What are the risks and benefits of irradiating food with cobalt-60?

Mathematical Modeling and the Physical World

• Physics phenomena are most clearly described via mathematical models. Mathematics allows the description of concepts, while also enabling predictions and design solutions for practical problems.
• Examples of worthwhile mathematics applications include data collection and analysis, graphical representations of data, measurement, and calculations. Emphasis must be placed on using calculations within real-world contexts so that students can see the relevancy of the numbers being calculated.
• Examples of calculations and analyses of information include those related to speed, velocity, acceleration, periods of vibration, wavelength, and frequency as well as kinetic and potential energy, mirror and lens images, Doppler effects, and conservation of matter and energy.