Issuu on Google+

Full file at

Laboratory Suggestions, with Answers to Lab Manual Questions  Introduction and Part 1 Activities and Experiments Introduction

Tuning the Senses - Observation Making Cents - Scientific Method

Part 1: Mechanics

Go! Go! Go! - Graphing Motion Sonic Ranger - Graphing Motion Pulled Over - Newton’s Second Law Reaction Time - Free Fall Egg Toss - Impulse Bouncy Board - Impulse Rolling Stop - Energy Transformations The Big BB Race - Horizontal and Vertical Motion

Tuning the Senses [Activity] This activity may be assigned as an "outside experience" (or homework), to be followed up later during classroom discussion. For the second half of this activity, watching the burning candle, for a large class of 28 students or so you will probably want to use four groups of seven, (or seven groups of four), with one candle per group, as it might be impractical and unnecessary to burn 28 candles, or more, per class. Again, you may choose to assign this as an "outside experience", and avoid clean-up and potential fire problems. This activity may easily be converted into an experiment by having a student in each group measure and record the candle's length and diameter before and after burning for a recorded time. The hypothesis to be tested could be, "The change in length per minute while burning is not directly proportional to diameter."

Making Cents [Activity] Brad Huff at The Fresno County Office of Education in Fresno, CA is credited for this activity. He discovered in 1984 that there was nearly an equal distribution of pre/post 1982 pennies in circulation. His students discovered the difference in mass as part of an exercise on how to use mass balances. So point out to your students the role of a good scientific attitude in making "accidental" discoveries—this one could have been overlooked as "human error." The composition of the alloy in pennies was changed in 1982. Pennies since 1982 are 2.500 g; from 1944 1982 pennies were 3.110 g; rare 1943 pennies were 2.700 g; and prior to 1942, pennies were 3.110 g. Such differences ordinarily escape our notice. A student can enter data on a chart written on the chalkboard. Students then plot this data as a graph. Alternatively, students can enter their data into an analysis program on a personal computer. If your students have never made a histogram, show them how to set up the values on the horizontal axis for the mass of the coins, using perhaps mass increments of 0.1 gram. How much copper did the U.S. government save by switching to zinc filled pennies?


Full file at

About 2.6 grams per penny: post 1982: 0.444 g Cu and 2.13 g Zn Density of Copper = 8.920 g/cm3

Density of Zinc = 7.140 g/cm3

Students see an unexpected result. Ask for more hypotheses. Is it from a change in size or from a change in composition? They can measure size based upon the displacement of water. 100 pennies displace how much water? Time permitting, they can find the density of pennies. Answers to the Questions 1. Pennies dated before and after 1982 should show a double-humped histogram should result—indicating a change in a penny's material in 1982. 2. Worn coins have less mass than new ones. Dirty, oxidized coins may have more mass. 3. Nails, nuts, soft drink cans, blades of grass, heights of students, etc.

Go! Go! Go! [Activity] This activity affords students an opportunity to collect data from an observable event, make measurements, and plot a graph of the results. They can then interpret the graph. The car speed and size of table should allow at least four data points. Answers to Summing Up Questions 1. 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 direction of the moving car with constant speed. Line B shows a car moving in the “positive” direction and speeding up.

Sonic Ranger [Experiment] To some extent, this is a high-tech version of Go! Go! Go! in which the computer plots the graph. Sonic ranging technology is revolutionizing the teaching pedagogy for graph interpretation. The computational power of the computer combined with its ability to make rapid measurements of distance and time enable your students to see the graph on the monitor in real time (where was this when we first learned about graphs!). Sonic ranging kits are available from a variety of sources. Contact Pasco Scientific, 10101 Foothill Blvd, Roseville, CA 95678 (800) 772-8700, or Vernier Software, 2920 S.W. 89th St, Portland, OR 97255, (503) 2975317 [Fax 503 297-1760]. Answers to Procedure Questions 1. 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.

Ti me t (seconds)

Full file at


Ti me t (seconds) Posi ti on x (meters)


Ti me t (seconds) Posi ti on x (meters)

Answers to Summing Up Questions 1. 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.

Full file at

Pulled Over [Experiment] Students can work in groups of three or four. With small tables, a group can work at each end, and with large tables, a group can work at each corner. Understanding the role of friction is the least of the objectives of this activity, so the less the friction between the book (or other object you decide to use) the better. Answers to the Questions 1. Greatest acceleration is the two-book drop and the one-book drag. Mid acceleration is the single-book drop and single-book drag, and least acceleration is the one book drop and the two-book drag. 2. Two books have both twice the force (gravity) and twice the mass, so acceleration is g (Figure 3.15 in the text). 3. Acceleration is less than g because the mass of the system is now twice but the gravity force of one dropping book is the same. Without friction, the acceleration would be one-half g. In terms of Newton's second law, ideally, a = = = g/2. 4. Acceleration would increase when the force that produces the acceleration increases. When three books are dropped, and drag a single book, acceleration is predictably greater. Ideally, a = = = 3/4 g. 5. The upper limit is g! Consider a dropping truck dragging a feather—the feather has negligible influence on the falling truck. 6. Friction was likely very significant, and perhaps greatly masked the idealized results above. Friction of sliding can be reduced by low-friction wheels beneath the dragged books or other objects, or even by using an air track. Friction of the twine at the table's edge can be reduced by the use of pulleys.

Reaction Time [Activity] This activity can easily be converted into an experiment by dividing the class into three groups, and recording measurements. A hypothesis could be that there is no significant difference in reaction time for the sense of sight, hearing or touching. Group "A" would measure reaction times for several students using a sight signal—they see the holder drop the bill. In Group "B" they close their eyes, and hear the holder say "Drop!" at the instant of release. In Group "C" they close their eyes, and receive a simultaneous tap on the shoulder from the dropper's other hand. A fourth group could explore the hypothesis that reaction times would differ between using a wooden 12 inch rule and a wooden meterstick—the meterstick is heavier, and would fall (a) faster? Or (b) slower? Or the (c) same? What if the rule were made of steel? [Same, of course!] If you happen to have a sub-group of psychology or political science majors, suggest a hypothesis that persons who believe (a), (b), or (c) will report data that supports their expectations. You may have a future doctor who is ready to understand a "double-blind experiment"! Answers to the Questions 1. Evidence ought to be the comparison between sound, sight, and touch on reaction time. 2. For one thing, the individual differences among people. 3. Reaction time can affect measurements that change with time. When the changes are small compared to reaction time, then the effects may be negligible. When they're not, for example in timing a falling object, then choosing the longest time interval lessens the error due to reaction time. Just like measuring the thickness of a page is more accurate when more pages are measured at one time. 4. Reaction time plays an important role in driving. For a reaction time of 0.7 second, a car going 100 km/h (28 m/s) travels nearly 20 m (about 60 feet) in 0.7 s, which is considerable— which has too many times been fatal. 5. In many sports, a single second is a long time. Baseball is an obvious one, where top players must have extraordinary reaction times. Likewise for soccer, football, and even boxing. The winners of races of all kinds usually are discerned in fractions of a second.

Full file at

Solution manual conceptual physical science 1st edition hewitt