Part 1: PhysicsWalking the PlankGo! Go! Go!Sonic RangerPutting the Force Before the CartReaction TimeEgg TossBouncy BoardAn Uphill ClimbRolling StopDropping the BallThe WeightThe Big BB RaceBull’s EyeTire Pressure and 18-WheelersSink or SwimEureka!Boat FloatDance of the MoleculesTemperature MixSpiked WaterSpecific Heat CapacitiesCanned Heat ICanned Heat III’m Melting! I’m Melting!Cooling by BoilingWarming by FreezingA Force to be ReckonedCharging AheadOhm, Ohm on the RangeBatteries and BulbsAn Open and Short CaseBe the BatteryThree-Way SwitchMagnetic PersonalityElectric MagnetismMotor MadnessGenerator ActivatorSlow-Motion WobblerSound OffPinhole ImagePinhole CameraMirror, Mirror, on the WallTrapping the Light FantasticA Sweet MirageDiffraction in Action

Laser Tree

Walking the Plank [Activity]This activity centers on the questions that led textbook author Paul Hewitt to study physics. The key finding here is that the net force for a body in equilibrium is zero. The forces that support the plank need not be equal to each other, but they will add to an amount equal to the weight being supported.

Answers to Procedure Questions1. Answers vary with the wide variety of metersticks in circulation. Older metersticks tend to be heavier and easier to get readings from.2. Forces L and R should be about equal to each other, and W = L + R.3. Zero (or nearly zero).4. Answers will vary, but should be about 4 N greater than the value reported in question 1.6. Zero (or nearly zero).7. The value should be the same as the value reported in question 4.9. Zero (or nearly zero).10. The net force must be zero.11. Answers will vary, but should be 7 N greater than the value reported in question 1, and equal to the sum of the scale readings found in Step 8.12. Answers will vary, but should be equal to the difference between the value reported in question 11 and the measurement recorded in Step 10.13. Answers will vary; most students find their measurement matches their prediction.14. About 25 cm.

Answers to Summing Up Questions1. Yes—as observed in Steps 4–5, for example.2. Yes—as observed in Steps 6–7, for example.3. Yes. The support forces would balance the weight, so the net force would be zero.4. The 200-g mass needs to be 2.5 times farther from the center of the meterstick than the 500-g mass. If the 500-g mass is 20 cm from the center, the 200-g mass would need to be placed at the 100-cm mark (2.5 × 20 cm = 50 cm from the center).5. The 200-g mass would have to be 75 cm away from the center of the meterstick, so this is not possible.

Go! Go! Go! [Experiment]This experiment affords students an opportunity to collect data from an observable event,make measurements, plot a graph of the results, then interpret the graph. The car speed and size of the table should allow at least four data points.

Answers to Summing Up Questions1. a. The marks would be farther apart. b. The car would reach the edge in fewer seconds.

c. The slope would have been steeper (more vertical).2. A steeper straight line should be added to the graph.3. a. The marks would be closer together. b. The car would take more seconds to reach the edge. c. The slope would have been shallower (more horizontal).4. A shallower straight line should be added to the graph.5. a. The marks would get closer and closer together. b. A curved line having a decreasing slope (concave down) should be added to the graph.6. Line A shows an object moving in the opposite (“negative”) direction compared to thedirection of the moving car with constant speed. Line B shows a car moving in the “positive” direction and speeding up.

Sonic Ranger [Activity]To some extent, this is a high-tech version of “Go! Go! Go!” in which the computer plots the graph. Sonic ranging has revolutionized the pedagogy for graph interpretation. Students making real time measurements and seeing the graphical representation of their own motions on a monitor are truly remarkable (where were these when we were students?).

Answers to Procedure Questions1. Remain at rest.2. Move away from the sensor (slowly).3. Move away from the sensor (more quickly).4. Move toward the sensor, slowing down as you approach it.5.

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Answers to Summing Up Questions1. Forward motion results in an upward (positive) sloping graph. Backward motion results in a downward (negative) sloping graph.2. Slow motion results in a line with a shallow slope; fast motion results in a line with a steep slope.3. First segment: speeding up; second segment: moving forward with constant speed; third segment: slowing down; fourth segment: at rest; fifth segment: moving backward with constant speed.

Putting the Force Before the Cart [Experiment]This experiment allows students to develop Newton’s second law (a = F/m) from directlaboratory experience. First, they find that the acceleration of an object is directly proportional to the net force acting on it. Next, they find that the acceleration of an object is inversely proportional to the mass of the object. Newton’s second law is the synthesis of these findings.