Errata for Interactions TG

Activity 36, p. 216, question A4 answer

Quadrant (column 1) should be "2 only", angle relative to horizontal (column 2) should be "27°", and angle relative to East axis (column 3) should be "153°".

Activity 36, p. 217

Answer to question B2 should be: 580m @ 149°.
Answer to question B3 should be: 500m @ 307°.
Answer to question B3, bullet 1: replace -37° with -53°.

Activity 37, p.222, "Suggested Points for Class Discussion", bullet 2

The word 'needs' should be 'need', i.e., "... both the origin and the orientation of the coordinate frame need to be specified..."

Activity 38, p. 227, question A5 answer

All the answers for vector V are wrong. There should be a minus sign in front of each term, and the length of the vector is 4.24cm. So, the x-component of V can be written either -(4.24cm) cos(45°) or -(4.24cm) sin(45°), and the y-component of V can be written either -(4.24cm) sin(45°) or -(4.24cm) cos(45°).

Activity 38, p. 229, question B5 answer, bullet 2

Change B3 to B2, i.e., "Students might use a rotated coordinate system (as in B2)."

Activity 42, p. 258, question B1 answer, bullet 1

Rephrase third sentence to read, "This is the only situation in this part for which buoyancy is considered relevant."

Activity 44, p. 267, "Probing for Student Understanding"

Change part (b) of question P3 to read, "In part B, how would the readings on scales A, B, and D change if scale C were removed?"

Activity 45, p. 280

In the answer to question I7, add object E to the list, i.e., "Only objects A, B, D, and E must have friction forces exerted on them."
The answer to question R3 is missing. It should read, "The objects considered in situations A3, A6, and B3 could be accelerating. For the rest, the object has a constant velocity.
There are no comments for R3. They are,
"Students might not include A3, perhaps because they think the ball is not accelerating at the top of its trajectory."
"Students might include B1, perhaps because the book is accelerating. But the object being considered is the table, which is not accelerating."
"Students might not include B3, perhaps because they think that the ball is at rest when it is touching the wall."
"At this point in the course, students are not expected to know the relationship between force and acceleration. Students should be encouraged to determine which objects definitely have no acceleration. The rest can be considered to possibly be accelerating."
The answer for question R4 is missing. It should read, "(Students indicate any forces other than the seven introduced here that they have heard of. They then indicate if any of these other forces behave like any of the forces introduced here."

Activity 45, p. 281

The answer to question P5 is wrong. It should read, "If the spring was compressed rather than stretched, then the strings would be angled inward, rather than outward. In other words, object G would be hanging to the left of where its string is attached to C, and object H would be hanging to the right of where its string is attached to C."
The comment for the answer to question P5 does not fit any longer. It should read, "Students might not think it is possible for the spring to remain compressed between objects G and H."

Activity 46, p. 284, "(More Ways of) Probing for Student Understanding"

Question P6 is question P4.
Question P7 is question P5.
Question P8 is question P6.

Activity 47, p. 294, question R2 answer

Change 'part B' to 'part A', i.e., "In situation C of part A, the normal force..."

Activity 48, p. 297, "Suggested Points for Class Discussion", bullet 2, last sentence

The word 'a' should be 'at', i.e., "(Thus, one can be at rest; the friction is still kinetic.)"

Activity 49, p. 307

The first entry in the table is not the beginning of the answer to question A4, but a continuation of the answer to question A3.
The answer to question A4 begins with gravitation.
There is a force missing from the answer to question A4. The force (i.e., column 1) is "kinetic friction." The way it will be determined (column 2) is "Multiply the normal force by the coefficient of kinetic friction. Direction is opposite the motion of _m_₁." The magnitude & direction (column 3) is "(NA)." Comment is "• We do not actually know the normal force, so we cannot determine the force of kinetic friction. However, students might think that they know the normal force using common sense."

Activity 49, p. 308, question R1 answer

The second bullet for air resistance is wrong. It should read, "At very small speeds, the force law is closer to Bv.

Activity 51, p. 324

The answer to question B1, part (a) is wrong. The x-component of F_{_N_,left} should be F__{_N},left.
The answer to question B1, part (b) is wrong. The x-component of F_{_N_,right} should be -F__{_N},right.
The answer to question B2, part (c) is confusing. Vectors F_{_g_1}, F_{_N_2}, and F_{_T_2} are not part of the answer. They are simply the other vectors in the situation, which are included because their components are known.
The answer to question B2, part (d) is wrong. The x-component of F_{_g_2} should be -F__{_g_2} cos 60°, and its _y-component should be -_F__{_g_2} sin 60°.
The word "the" should be removed from the second line of the last bullet for the answer to question B2, i.e., "Even if we notate the magnitude of both tension forces as..."

Activity 54, p. 350, question P9 answer

Change "velocity" to "velocities", i.e., "(a,b) The forces... Kinetic Friction, which depends on the relative velocities of the objects in contact, and..."

Activity 55, p. 357, question A5 answer

In the table showing the time intervals during which the ball is accelerating, change '4.9s' to '4.8s', i.e., the time interval corresponding to the 2nd time the ball is rolling across the felt should be [4.8s, 6.5s].
In the table showing time intervals during which its velocity is constant (it's part of the 4th bullet of the answer to question A5), change '4.9s' to '4.8s', i.e., the third time interval during which the ball is rolling at constant velocity is [3.51s, 4.8s].

Activity 56, p. 370, question C4 answer, bullet 3

Change 'any' to 'a', i.e., "Students might not perceive that there is a net force on them when they walk in a circle."

Activity 58, p. 384, question A2, part (c) answer

Of the three free-body diagrams, the one on the left is for the skydiver, the one in the middle is for the parachute, and the one on the right is for the Earth.

Activity 58, p. 386, question B4 answer

Add to the end of the answer to part (b): "But perhaps not as much faster and farther as before, assuming for example that she does not push as hard as her father did before."
Add a bullet: "• In other words, her speed might be smaller than it was before, but it is always larger than her father's."

Activity 58, p. 387, question R1 answer, bullet 1

Change to "The action-reaction pair has five features: exerted by different objects, exerted on different objects, same type (normal, gravitational, etc.), same magnitude, and opposite direction."

Activity 59, p. 389, "Suggestions for Classroom Use"

Change bullet 2 to: "Focus students' attention on learning the answers and explanations to two questions using the following group structure: Divide the class into teams of 3 or 4 students each. Assign each team 2 questions from the same part, or put slips of paper with the numbers of 2 questions into a bowl and have teams choose. Tell students that each of them will be asked to write out the explanation to one of the questions, and that each student's grade will depend in part on how well the other team members do. As the teams are working, decide which explanation each student will provide. When the working time is complete, give students their assignments, to be done either during or after class. When grading explanations, give half credit for each individual's contribution and half credit for the contributions of the rest of the team. In other words, half of each student's grade will depend on his/her individual explanation, and the other half will depend on his/her team's explanations.
Insert between bullets 2 and 3: "• For small classes with only a few teams, do parts B and D first, then repeat with parts C and E."
Add bullet: "• As a class, compare answers and discuss areas of disagreement."

Activity 59, p. 391, question A4 answer

Change 'rope 1' to 'rope 2', i.e., "... then the tension in rope 2 is larger in case II than in case I."

Activity 59, p. 392, question C2 answer

Add bullet: "• Students might think that the velocity is larger because the net force is larger."

Activity 60, p. 402, question R2, part (a) answer

Remove 'of the', i.e., "The mass is much larger for the car."

Many thanks to Lonnie Grimes of Oakmont High School in Roseville, CA, who found almost all of these mistakes.