Goal: Students are introduced to the idea of conservation as a foundational principle of physics, along with the concept of work as the primary agent of change for energy. As in earlier units, students will once again utilize both familiar and new models and representations to analyze physical situations, now with force or energy as major components. Students will be encouraged to call upon their knowledge of content and skills in Units 1 and 2 to determine the most appropriate technique for approaching a problem and will be challenged to understand the limiting factors of each technique.
To access the main folder and get class notes and additional practice problems per each topic below click the following link:
AP Physics 1-Unit 3-Work, Energy and Power
(time to complete all WebAssign Problems approximately 7hr 14min)
**You will take 1 test during this unit.**
Learning Objective:
-Describe the translational kinetic energy of an object in terms of the object’s mass and velocity.
Essential Knowledge:
-The translational kinetic energy of an object is related to the mass and translational velocity of the object.
-Translational kinetic energy is a scalar quantity.
-Different observers may measure different values of the translational kinetic energy of an object, depending on the observer’s frame of reference.
Skills:
-Create qualitative sketches of graphs that represent features of a model or the behavior of a physical system.
-Calculate or estimate an unknown quantity with units from known quantities, by selecting and following a logical computational pathway
-Apply an appropriate law, definition, theoretical relationship, or model to make a claim
-Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws
Read & Take Notes on Sections: 5.1, 5.2
WebAssign: Ch5 - 1, 3, 4, 6, 7, 13, 18
Learning Objective:
-Describe the work done on an object or system by a given force or collection of forces.
Essential Knowledge:
-Work is the amount of energy transferred into or out of a system by a force exerted on that system over a distance.
-The work done by a conservative force exerted on a system is path-independent and only depends on the initial and final configurations of that system
-The work done by a conservative force on a system—or the change in the potential energy of the system—will be zero if the system returns to its initial configuration.
-Potential energies are associated only with conservative forces.
-The work done by a nonconservative force is path-dependent.
-Examples of nonconservative forces are friction and air resistance.
-Work is a scalar quantity that may be positive, negative, or zero.
-The amount of work done on a system by a constant force is related to the components of that force and the displacement of the point at which that force is exerted.
-Only the component of the force exerted on a system that is parallel to the displacement of the point of application of the force will change the system’s total energy.
-The component of the force exerted on a system perpendicular to the direction of the displacement of the system’s center of mass can change the direction of the system’s motion without changing the system’s kinetic energy.
-The work-energy theorem states that the change in an object’s kinetic energy is equal to the sum of the work (net work) being done by all forces exerted on the object.
-An external force may change the configuration of a system. The component of the external force parallel to the displacement times the displacement of the point of application of the force gives the change in kinetic energy of the system.
-If the system’s center of mass and the point of application of the force move the same distance when a force is exerted on a system, then the system may be modeled as an object, and only the system’s kinetic energy can change.
-The energy dissipated by friction is typically equated to the force of friction times the length of the path over which the force is exerted.
-Work is equal to the area under the curve of a graph of F as a function of displacement.
Skills:
-Create quantitative graphs with appropriate scales and units, including plotting data.
-Calculate or estimate an unknown quantity with units from known quantities, by selecting and following a logical computational pathway.
-Predict new values or factors of change of physical quantities using functional dependence between variables.
-Create experimental procedures that are appropriate for a given scientific question.
-Apply an appropriate law, definition, theoretical relationship, or model to make a claim.
Read & Take Notes on Sections: 5.1, 5.2, 5.8
WebAssign: Ch5 - 1, 3, 4, 6, 7, 13, 18, 59, 61
Learning Objective:
-Describe the potential energy of a system.
Essential Knowledge:
-A system composed of two or more objects has potential energy if the objects within that system only interact with each other through conservative forces.
-Potential energy is a scalar quantity associated with the position of objects within a system.
-The definition of zero potential energy for a given system is a decision made by the observer considering the situation to simplify or otherwise assist in analysis.
-The potential energy of common physical systems can be described using the physical properties of that system.
-The elastic potential energy of an ideal spring is based on the distance the spring has been stretched or compressed from its equilibrium length and the spring constant (force constant).
-Because the gravitational field near the surface of a planet is nearly constant, the change in gravitational potential energy in a system consisting of an object with mass m and a planet with gravitational field of magnitude g when the object is near the surface of the planet may be approximated by the expression mgh.
-The general form for the gravitational potential energy of a system consisting of two approximately spherical distributions of mass (e.g., moons, planets or stars) which is different from the expression mgh.
-The total potential energy of a system containing more than two objects is the sum of the potential energy of each pair of objects within the system.
Skills:
-Create qualitative sketches of graphs that represent features of a model or the behavior of a physical system.
-Compare physical quantities between two or more scenarios or at different times and locations in a single scenario.
-Predict new values or factors of change of physical quantities using functional dependence between variables.
-Apply an appropriate law, definition, theoretical relationship, or model to make a claim.
Read & Take Notes on Sections: 5.3, 5.5, 7.5
WebAssign: Ch5 - 19, 20, 23, 25, 64, 69 ; Ch7 - 39 & Ch13 - 11
Learning Objective:
-Describe the energies present in a system.
-Describe the behavior of a system using conservation of mechanical energy principles.
-Describe how the selection of a system determines whether the energy of that system changes.
Essential Knowledge:
-A system composed of only a single object can only have kinetic energy.
-A system that contains objects that interact via conservative forces or that can change its shape reversibly may have both kinetic and potential energies.
-Mechanical energy is the sum of a system’s kinetic and potential energies.
-Any change to a type of energy within a system must be balanced by an equivalent change of other types of energies within the system or by a transfer of energy between the system and its surroundings.
-A system may be selected so that the total energy of that system is constant.
-If the total energy of a system changes, that change will be equivalent to the energy transferred into or out of the system.
-Energy is conserved in all interactions.
-If the work done on a selected system is zero and there are no nonconservative interactions within the system, the total mechanical energy of the system is constant.
-If the work done on a selected system is nonzero, energy is transferred between the system and the environment.
Skills:
-Create diagrams, tables, charts, or schematics to represent physical situations.
-Derive a symbolic expression from known quantities by selecting and following a logical mathematical pathway.
-Compare physical quantities between two or more scenarios or at different times and locations in a single scenario
-Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws.
Read & Take Notes on Sections: 5.4, 5.6
WebAssign: Ch5 - 32, 36, 37, 47
**Note**
-Students are expected to know that mechanical energy can be dissipated as thermal energy or sound by non-conservative forces.
Learning Objective:
-Describe the transfer of energy into, out of, or within a system in terms of power.
Essential Knowledge:
-Power is the rate at which energy changes with respect to time, either by transfer into or out of a system or by conversion from one type to another within a system.
-Average power is the amount of energy being transferred or converted, divided by the time it took for that transfer or conversion to occur.
-Because work is the change in energy of an object or system due to a force, average power is the total work done, divided by the time during which that work was done.
-The instantaneous power delivered to an object by the component of a constant force parallel to the object’s velocity can be described with a derived equation.
Skills:
-Create quantitative graphs with appropriate scales and units, including plotting data.
-Derive a symbolic expression from known quantities by selecting and following a logical mathematical pathway.
-Compare physical quantities between two or more scenarios or at different times and locations in a single scenario.
-Create experimental procedures that are appropriate for a given scientific question.
-Justify or support a claim using evidence from experimental data, physical representations, or physical principles or laws.
Read & Take Notes on Sections: 5.7
WebAssign: Ch5 - 50, 57, 58 & Ch5 AP Multiple-Choice Review Questions
Test #5