# Physics

In Cambridge, we believe that by introducing students to physics as Freshman we are setting a foundation of knowledge that will allow them greater success in chemistry and biology. All 9th graders begin their time at CRLS in a heterogeneously grouped physics course, with an honors option.

In Grade 9 Physics, instructional time should focus on four critical areas:

1. Forces and motion;
2. Forms of energy;
3. Electrical and magnetic energy; and
4. Sound and light energy
 Unit Learning Goals Motion Explain why variables are vectors or scalars Describe relationships between displacement, distance, velocity, speed, and acceleration Find velocity or time given acceleration. Describe the motion shown in a position-time or velocity-time graph with two or more segments (limited to constant velocity for position-time) Interpret complex graphs Draw graphs of particular situations Calculate acceleration (slope) from a velocity-time graph Calculate distance traveled from a velocity-time graph in which the velocity changes uniformly Describe how Newton’s Laws relate to common situations (i.e. seatbelts) Recognize situations in which force or weight needs to be calculated as the first step of a problem Solve simple two-step problems involving force and acceleration Draw free-body diagrams of objects with forces in two-dimensions (right angles only). Use information from a problem to draw a free-body diagram. Describe the affect of friction on the motion of an object Make qualitative predictions about the motion of objects in collisions Make predictions about how the gravitational force changes when mass and distance are changed Conceptually describe forces in uniform circular motion Electricity Explain how electrons are transferred when objects are charged by friction or contact. Explain the cause of polarization and give an example. Understand how conductors and insulators affect the flow of electrons. Determine the net charge on an ion. Solve Coulomb’s Law formula for F with or without using scientific notation. Qualitatively describe the relative effects of distance and charge on the electric force. Describe the relationships between voltage, current and resistance. Apply V=IR to simple series circuits. Draw schematic diagrams of both series and parallel circuits. Describe what happens when a circuit is open. Build series and parallel circuits that include switches. Differentiate behavior of series and parallel circuits. Describe conceptually the relationships between P, I, and V. Solve two-step electric circuit problems involving P=IV and V=IR. Recognize that moving electric charges produce magnetic forces and that moving a magnet produces an electric force. Give examples of applications of electromagnetism (motors and generators). Waves Define pitch and volume with wave properties Draw wave graphs with a given period, frequency and amplitude Draw a graph of frequency versus wavelength Describe the motion of the medium in transverse and longitudinal waves Draw transverse and longitudinal waves Compare sound graphs based on frequency (pitch) and amplitude (volume) Change the frequency of a musical instrument Give an example that compares the speed of sound in two materials Explain and/or draw why frequency of a wave seems to change based on the motion of a sound source or receiver Compare and contrast sound and light waves Understand how the properties of mechanical and electromagnetic wave affect their use in outer space Compare incident and reflected rays with respect to the normal Relate the change in angle of a light ray to a change in speed of light. Use c = fλ to solve for frequency or wavelength For each section of the electromagnetic spectrum, describe at least one way that humans interact with it. Energy Explain with examples how work affects gains or losses in an object’s mechanical energy. Explain qualitatively how force and distance affect work done. Solve two-step problems (i.e. calculating weight to solve for work or solving for work and then power) Compare two objects based on their power output. Solve two-step problems (i.e. compare the power of two objects or calculate work in order to find power) Explain that total energy includes not only mechanical, but also includes thermal, chemical, electrical, etc. Use PE = mgh to solve for mass, acceleration of gravity, or height. Use KE = 1/2mv2 to solve for mass Interpret and explain heat and temperature graphs Distinguish between temperature and total heat energy Explain what would happen to a material if its temperature dropped to absolute zero Define specific heat Use Q = mcΔt to solve for mass, specific heat, or change in temperature Explain, on a molecular level, the process of heat transfer in each of the three methods Identify factors that affect the rate of heat transfer (i.e. lightness or darkness of an object affects how well it absorbs radiation)
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