What is the connection between force, motion, and energy?
In this unit students investigate forces and energy transfers in interactions between objects. The fundamental concept is that the evidence of an interaction is a change in the motion or energy of an object. Students compare examples of contact forces as pushes or pulls between interacting objects that are touching. They also identify gravitational, magnetic, and electrostatic interactions as non-contact forces. Since the emphasis in a conceptual physics course is on understanding fundamental ideas that explain everyday phenomena, activities that involve the concept should come before the formal introduction of the concept. Students have multiple opportunities to calculate the net force when two or more forces are acting on an object. When unbalanced forces are applied to an object, students qualitatively recognize that an acceleration occurs. This lead to an understanding of the direct relationship between net force and acceleration (F=ma). Next, students observe and measure action/reaction forces using paired force scales with students pulling away from each other or from a stable object like a wall. They then explain why these action/reaction pairs do not cancel each other out and prevent motion. Finally, students investigate energy transfer in interactions. They distinguish between and calculate the kinetic energy (energy of moving objects) and the potential energy (energy stored due to position or shape) of objects in various situations such as a person jumping or a bouncing ball. The back and forth conversion of kinetic and potential energies in this situation is also analyzed. At this point the scientific concept of work as energy transfer is also introduced.
- What is the evidence for the existence of forces?
- What is the difference between contact and non-contact forces?
- How do balanced and unbalanced forces affect an object?
- How are kinetic and gravitational potential energy related in energy transfers?
- How is work related to the transfer of energy?
- What is the role of friction in everyday interactions?
balanced and unbalanced forces
coefficient of friction
elastic potential energy
frame of reference
gravitational potential energy (GPE = mgh)
kinetic energy (KE = ½ mv2)
Newton’s 1st Law
Newton’s 2nd Law (F = ma)
Newton’s 3rd Law
How is physics useful in describing and analyzing collisions?
In this unit students examine collisions between objects. They observe several different collisions between objects of different masses moving at different speeds. Then students represent the motion of objects using measured values of distance and time, stroboscopic motion diagrams and graphs of distance vs. time and velocity vs. time in diagrams such as those produced by calculator based ranger (CBR) motion detector units. Next they examine the relationship between the impact time and impact force in a collision - what scientists call impulse. This leads to a discussion and eventual comparison of various safety devices such as seat belts, helmets, and airbags along with the physics principles behind them. Students then qualitatively relate the impulse of the objects in a collision to the mass of the objects and their resulting change in velocity. Lastly, students measure the speeds and calculate the momenta of different objects before and after a collision such as billiard balls or toy train cars. Then these momenta are analyzed, leading to a discussion of the measured differences in the before and after momenta and eventually the Law of Conservation of Momentum.
- How are the time of impact and the force related during a collision?
- How are the masses of the objects and the resulting changes in velocity related to each other in a collision?
- How does the total momentum before and after a collision relate to each other?
- How do technological devices such as seat belts, helmets, and air bags work to reduce injuries in a collision?
- How can the motions of the objects in a collision be represented and analyzed?
change in momentum (∆p = m∆v)
conservation of momentum
impulse (Ft = m∆v)
How is motion measured and described?
In this unit students investigate and describe the motions of people and objects in everyday situations such as sporting events. Initially, students measure the distance traveled during equal time intervals for objects traveling at a variety of constant speeds. Next, they measure the distance an object moves in equal time intervals when it is speeding up and slowing down. This distance and time data for various moving objects are used to make distance vs. time line graphs to represent these motions, along with motion diagrams, to show the positions at equal time intervals. These graphs are then used to develop the relationship between the slope of the graph and the speed of the object. Specifically, constant slope means constant speed and changing slope means changing speed. Students also use the formula for average speed to compare the motions that were measured. They then construct velocity vs. time graphs to represent these same motions and use given velocity vs. time graphs to construct verbal descriptions of motion. Last, students investigate circular motion by identifying and representing on diagrams the center seeking, or centripetal force, required to maintain circular motion in a frictionless environment. In each case, the primary objective is to develop the understanding that all motion is measured in terms of distance traveled in a fixed time interval and to relate this understanding to the concepts of average speed, constant speed, and acceleration.
- How do scientists describe the motion of objects?
- How can the motion of objects be represented by line graphs, motion diagrams, and formulas?
- How are average speed, distance traveled, and acceleration calculated using appropriate formulas and graphs?
- What causes objects to move in circular paths?
graphs of motion
How can roller coasters be used to understand energy and forces?
In this unit students investigate the transfer between kinetic and potential energy on a roller coaster ride. First, students represent a roller coaster ride using a sketch of the track based on their previous experiences, video, or online simulation. Then they use the concepts of force and acceleration to describe when a rider might feel heavier or lighter than usual on the ride. This leads to a discussion of the different types of forces and resulting accelerations experienced by a rider. Students then describe the centripetal forces and accelerations required to keep the roller coaster on the track during various size curves and loops. They explore how the mass and position of an object, relative to the earth, impacts its gravitational potential energy. Last, students keep track of the transfers between kinetic and potential energies of the roller coaster during the ride. After the roller coaster reaches its highest position, it is a closed system and energy no longer enter the system. Students then use suitable initial conditions to calculate the kinetic energy and potential energy at various points on the ride and show that the total energy remains constant.
- How is the kinetic energy (KE) of an object determined?
- How is the potential energy (PE) of an object determined?
- What is the relationship between the kinetic and potential energies of a rider at different points on a roller coaster?
- What are the forces and accelerations experienced on a roller coaster ride?
- What part of a roller coaster ride produces the greatest thrill?
- How do scientists account for the “missing” energy during a roller coaster ride?
centripetal acceleration (a=v2/r)
conservation of energy
gravitational potential energy (∆GPE = mg∆h)
kinetic energy (KE = 1/2mv2)
Newton’s 2nd Law (F = ma)
How are physics ideas used to explain sound and light?
In this unit students investigate the characteristics of waves. Throughout the unit students contrast sound and light as particular examples of mechanical and electromagnetic waves. They examine transverse and longitudinal (compressional) waves on a Slinky™ or with online simulations. These simple but engaging tools allow students to experience first hand both types of waves and make basic observations and measurements of frequency, wavelength, amplitude, and wave speed, and their relationship. Additionally, the observation that waves transfer energy with no net transfer of mass is an important concept to allow for the comparison with how a moving object transfers energy. Net the relationship between the amount of energy transferred and the wave’s characteristic properties is addressed. Students then explore sound waves produced by vibrating strings and columns of air with special attention paid to identifying the source of vibration in various musical instruments along with the propagation of sound, so that everyone in a room hears the same notes simultaneously. They represent the reflection and refraction of light rays from mirrors and through transparent materials, such as lenses, using ray diagrams to show the behavior of light and the location and size of images produced. Students then compare the sources and nature of both sound and light waves emphasizing their similarities and differences. Finally they explore the identifying characteristics of surface waves and how they function to cause tsunamis and damage during earthquakes.
- What are the defining characteristics of waves?
- How is energy transfer by waves different from other forms of energy transfer?
- How are sound and water waves different from and similar to light waves?
- How are sound waves produced?
- How is light reflected from plane and curved mirrors?
- How is light refracted by transparent materials and lenses?
compression (longitudinal) waves
How is the transfer of heat energy impacted by materials and design?
In this unit students investigate energy transfer in homes which are constructed using different material and designs. The emphasis is on heat transfer and practical ways to prevent energy loss in homes and other buildings. Students are organized into teams to identify common characteristics and shapes of dwellings and how surface area and volume are related to actual living space. Then they investigate the relationship between the heating and cooling of a building and the impact of insulation and material types on the heat energy transfer between the building and its surroundings. Students also investigate the insulating properties of various materials by designing experiments to measure temperature change of hot and cold objects at various time intervals. Next they explore where insulation should be placed in a building to increase energy efficiency and factors that constrain the amount of insulation that can be used. Students explore the connection between the placement and size of windows, overhangs, and awnings with heating and cooling costs. This analysis is then expanded to include the effect of the sun’s altitude in the sky during different seasons. The unit concludes by students experimenting to determine the final temperature when two liquids of different temperatures are mixed and when a hot metal object is added to a container of cold water, which leads to the concepts of specific heat of materials, heat energy conservation, and entropy.
- What characteristics of materials influence their ability to block heat energy transfer?
- How does building design impact the transfer of heat energy?
- How is building efficiency improved by applying an understanding of the three mechanisms of heat energy transfer?
- Where should windows and awnings be placed to maximize a building’s energy efficiency?
How is electricity measured and used?
In this unit students explore the ways that current electricity is used and measured in common household devices. To accomplish this they try to light a bulb using a hand generator and wires. Then students investigate the effects of changing the speed and direction of cranking the generator or reversing the connections of the wires. Next, a strand of steel wool is substituted for the bulb and students compare the effects of varying amounts of electrical current from the generator on these two loads. This leads to the development of a circuit concept that consists of an electrical source, connecting conductors (wires), and a load or electrical device. Students investigate simple series and parallel circuits using multiple batteries and loads, such as bulbs, and begin to differentiate between current flow, voltage, and resistance in such circuits. This can be complemented by having students use an online circuit construction simulator such as the PheT Circuit Construction Kit (available online). These concepts are also connected to the language used in electrical measurements, volts, amps, and ohms. Further investigations lead to Ohm’s Law that describes the relationship between these electrical quantities. Students develop the idea of a circuit diagram and simple symbols as a way to represent and analyze circuits. The role of switches, short circuits, fuses, circuit breakers, and their placement in a circuit is then introduced. They investigate the concept of electrical power and the meaning of watts as a unit of power. This leads to the development of the idea of the flow of electrical energy and its transformation to other forms of energy in various appliances. Specifically, students investigate the different factors that effect the changes in water temperature when an electrical heating coil is used to heat water. This leads to further investigations of the typical energy usages by home electrical appliances and the analysis of how the electric power company determines one’s electric bill.
- What is electricity?
- What types of energy transformations take place in common electrical devices such as bulbs, motors, and heaters?
- In what ways can multiple devices be connected to an electrical source in a circuit?
- How are electrical circuits described and used?
- What roles do switches, fuses, circuit breakers, and electrical shorts play in electrical circuits?
- What are the relationships between current, voltage, resistance, and power in a circuit?
electrical power (P = IV)
moving electric charge
Ohm’s Law (V = IR)
What is the relationship between electricity and magnetism?
In this unit students investigate how electrical fields and magnetic fields interact to produce motion (electrical motors) or electricity (generators). First they explore the defining characteristics of magnets and their interactions with other magnets and magnetic materials. Then students do the same for electric charges and their interactions with various neutrally charged materials. This then allows them to compare and contrast magnetic interactions and electric charge interactions. Next students explore how the magnetic compass is used to detect current in a wire and to also note its directionality. This then leads to exploring the interactions between electrical fields and magnetic fields that can produce mechanical energy (motion) in a motor or produce electrical current and energy in a generator. This unit concludes with students building a simple electric motor and/or generator that is used to demonstrate these concepts. This provides a way to explain how these devices work using the basic interaction concepts learned in this unit.
- How are magnetic interactions and electric charge interactions similar and different?
- How can a magnetic field be used to move electric charges?
- How can electric charges be used to produce magnetism?
- What are the similarities and differences between motors and generators?
electrical current (AC and DC)
magnetic and electric forces
What characteristics of atoms do scientists use to understand matter?
In this unit students investigate the nature of the atom and how the particulate model of matter has developed. The fundamental purpose of this unit is to introduce students to this model and help them understand how this theory was developed and modified to account for everyday observations of the material world. Because atoms, the particles of the model, are extremely small and cannot be observed directly without sophisticated equipment, this unit will often use reading about the evidence collected by the scientists who were originally involved in making and interpreting these observations. Students can make certain observations and then use them to infer the validity and usefulness of the model. First, students explore the nature of electrical chargers and the nature of the forces between them. They then draw charge distribution diagrams of various charged and neutral objects. Then students are introduced to Coulomb’s Law and the electrical nature of all matter. Next they investigate the inferential methods used to measure the size of the atom and their electrical charge by using pennies hidden in film containers. The classic experiments of Rutherford and Millikan are introduced to account for the charge on the electron and the size of the nucleus. Students also observe with simple spectrometers the spectra emitted from H, He, and Ne sources. They review the model of the atom developed by Bohr and how it is used to explain ionization energy and atomic structure. Next the wave nature of electrons is introduced to account for the photoelectric effect. Then the further modifications of the basic Bohr model of the atom required by the wave-particle duality theory and the work of Schrodinger and others who developed quantum mechanics are introduced. Last the nucleus of the atom is introduced and how a very strong nuclear force is required to account for its small size, very large density with a strong electrostatic repulsive force. This then leads to investigating the probabilistic nature of radioactive decay using sugar cubes. A concluding discussion contrasting nuclear fusion and fission explores the mass-energy relationship in nuclear reactions and their potential as an energy source for a world that now relies on fossil fuels.
- What are the characteristics properties of atoms?
- How do scientists support the theory of the particulate nature of matter when the particles are too small to be observed directly?
- If most matter is composed of electrically charged particles, why does only some matter show evidence of charges?
- What evidence leads scientists to describe subatomic particles as having both wave and particle characteristics?
- What is the source of radioactivity and nuclear energy?
distribution of electric charge
electric charge (positive and negative)
inverse square law
mass to energy conversion E = mc2
How do fields and the theory of relativity help scientists understand the universe?
In this unit students are introduced to three force fields – magnetic, electric, and gravitational – and relates them to the bases upon which the theory of relativity was developed. This unit also explores the characteristics of good scientific theories and how they can be distinguished from pseudoscience suing fields and relativity as examples. First students map a magnetic field using a bar magnet and a compass to recognize that, while it is invisible, it can be measured and future observations predicted by using a scientific model of fields. Then they discuss the nature of an electric field by predicting the motion of a hypothetical test charge in an electric field. Next, the roles of mass and distance are explored in Newton’s Law of Universal Gravitation. Students observe the motion of a ball from a stationary position and while moving at a constant speed and then comparing these observations made when the observer is accelerating. These observations lead to a discussion of the importance of stating the frame of reference of the observer when making any observations. What follows from this is the concept of relativity in an inertial frame of reference. Next the role of the speed of light in the Theory of Special Relativity is explored using Einstein’s thought (or gedanken) experiments. Last, students explore the criteria for a scientific theory and contrast this with non-scientific or pseudoscientific claims. This latter discussion is particularly relevant in the Theory of Special Relativity where students’ concept of “common sense” is challenged.
- What are the similarities and differences between magnetic, electric, and gravitational fields?
- What determines the magnitude of the gravitational force?
- What is an inertial frame of reference?
- How does the frame of reference of an observer affect observations?
- What criteria must a theory meet if it is to be accepted as a good scientific theory?
- What roles does the speed of light play in the Theory of Special Relativity?
frame of reference
inertial reference frame
inverse square law
Newton’s Law of Universal Gravitation
non-scientific (pseudoscientific) claim
speed of light
Theory of Special Relativity
thought (gedanken) experiment
How are mass, weight, and gravity related?
In this unit students investigate the relationship among mass, weight, and gravitation by imagining sports on the moon. The premise for this unit is that one day a colony will be established there and that humans will one day live there for extended periods of time. Since sports provide necessary exercise and entertainment, provisions will need to be made for sports on the moon. Initially, students need to identify the essential characteristics of a sport of their choice. Then they brainstorm the possible changes needed to the rules and/or equipment for the adaptation of that sport to the moon colony. Second students investigate free fall, mass, weight, and the acceleration due to the moon’s gravity. They also have the opportunity to explore the derivation and origin of the equation d=1/2gt2 and apply this equation to free fall on the moon. Next the implications of changes (or lack of change) in these variables on projectile motion and jumping on the moon are analyzed. Students then use the independence of the horizontal and vertical components of projectile motion to compare this type of motion on earth with that on the moon. These factors can then be applied to a hypothetical game of golf on the moon and to the impact of frictional forces on both the earth and the moon. Next the question of why astronauts “bound” instead of walking normally on the moon is investigated by revisiting and analyzing pendula and relating this to the movement of an astronaut’s legs. Then students compare the motion of objects in an air-filled environment on the moon with the same objects’ motion on earth. Last they write a proposal to NASA to identify or invent a sport that people on the moon will find interesting, exciting, entertaining, and provide needed physical exercise.
- What factors influence free fall on the moon?
- How is projectile motion on the moon the same and different from that on the earth?
- How high could you jump on the moon?
- what is the impact of friction and drag on moving objects on the moon?
- How does walking and running on the moon compare to that on earth?
- How would motion in an air-filled environment on the moon be different from that on earth?
acceleration due to gravity
air resistance (drag)
horizontal and vertical components of motion
kinetic energy (KE=1/2 mv2)
Newton’s 2nd Law
Newton’s 3rd Law
How do scientists use electromagnetic (EM) waves to analyze and understand the universe?
In this unit students learn about how scientists make knowledge claims about the size and composition of the universe. The communication of information from the far reaches of the universe, by electromagnetic waves, form the basis for these claims; and therefore the foundation for our understanding of stars, galaxies, and the possibility of extraterrestrial life. First, students investigate large distances using d=vt and time delays in radio communications. This leads to using the distance unit of light-years to express astronomical distances. Next, both reflecting and refracting telescopes are introduced to explain how these instruments use combinations of lenses and mirrors to magnify apparent size of the object. Third, using the properties of wavelength and frequency, the electromagnetic spectrum is introduced. This range of different electromagnetic waves, called the electromagnetic spectrum, is discussed as a continuum of wavelength, frequency, and energy which is categorized into groups depending upon their technological uses. The existence of other telescopes, besides light telescopes, that make use of the entire electromagnetic spectrum to analyze the universe are also introduced. Fourth, students make a diffraction grating spectroscope to observe spectral lines and measure the wavelength of a given frequency of light. This leads to a discussion of how the spectra of each element is unique and can be used to identify the chemical elements present in the outer layers of stars and galaxies thousands of light-years from earth. Then the nature and use of digital representations of information are explored. Analog and digital forms of communicating information are investigated and compared. This is an excellent opportunity to discuss the current decisions of scientists and policy makers to transition from analog and digital communications.
- How are electromagnetic waves described and measured?
- How is the entire electromagnetic spectrum used to 'measure' and analyze the universe?
- How do combinations of lenses and/or mirrors produce images in light telescopes?
- How do scientists use all forms of electromagnetic radiation and spectra to infer the composition and nature of stars?
- How are digital communications (images, sounds, text, etc.) different from analog communications?
- Why are there noticeable time delays in radio communications between the earth and the moon?
emission (line) spectrum
speed of light