Chapter 9 Motion and Energy
Chapter 9 Level A
Describing Motion
Use Target Reading Skills
motion—what occurs when an object’s distance from another object is changing
reference point—an object or a place that you can use to tell if an object is in motion
distance—the length of the path between two points
displacement—the length and direction that an object has moved from its starting point
vector—a measurable quantity that consists of both a magnitude and a direction
1. motion
2. A reference point is a place or an object used for comparison to determine if something is in motion.
3. reference point
4. Relative to the plane and the car, you appear to be moving left to right in the figure.
5. Relative to the person on the sidewalk, you appear to be moving right to left in the figure. Relative to the plane, you do not appear to be moving much because the plane is moving in the same direction.
6. Relative to the person on the sidewalk, you appear to be moving right to left in the figure. Relative to the car, you do not appear to be moving much because the car is moving in the same direction.
7. displacement
8. c
9. vectors
Speed and Velocity
Use Target Reading Skills
Sample answers:
Main Idea: Changes in velocity may be due to
changes in speed, changes in direction, or both.
Detail: Velocity is speed in a given direction.
Detail: Velocity of a storm may be 25 km/h to the east.
Detail: If the storm changes direction but not speed, its velocity changes.
1. Speed = Distance/Time
2. Divide the total distance the cyclist traveled by the total time.
3. velocity
4. The direction in which it is moving
5. slope
6. trueGrade 8 Physical Science
7. 1,400 m
8. The jogger traveled no distance during these minutes; the jogger stopped.
Acceleration
Use Target Reading Skills
Sample answers:
Main Idea: To determine the acceleration of an object, you must calculate its change in velocity per unit of time.
Detail: Velocity has magnitude and direction.
Detail:
Detail: Acceleration might be measured in m/s2 or km/h2.
1. Acceleration is the rate at which velocity changes with time.
2. speed, direction
3. acceleration
4. true
5. acceleration
6. true
7. a, b, d
8. The moon is accelerating because it is constantly changing direction as it revolves around Earth.
9. (in left column) Speeding up; (in right column) Decreasing speed; Changing direction
10. The change in velocity during each unit of time.
11.
12. false
13. a, b, d
14. The speed increases over time.
15. The acceleration is constant.
Energy
Use Target Reading Skills
Sample outline:
Energy
I. Kinectic Energy
A. Energy an object has due to its motion
B. Kinetic energy = ! Mass ! Speed2
II. Potential Energy
A. Gravitational Potential Energy
1. Potential energy related to an object’s height
2. Gravitational potential energy = Weight ! Height
B. Elastic Potential Energy
1. Potential energy of objects that can be stretched or compressed
2. Example: archer pulling back on bow
III. Energy Transformation and Conservation
A. Transformations Between Potential and
Kinetic Energy
1. Any object that rises or falls experiences a change in its kinetic and gravitational potential energy.
2. Pendulum—continuous transformation between kinetic and potential energy
B. Conservation of Energy
1. Energy cannot be created or destroyed.
2. Energy is transformed, not destroyed.
1. energy
2. When an object or a living thing does work on another object, some of the energy is transferred to the second object.
3.
a. kinetic energy
b. potential energy
4. The energy an object has due to its motion
5. mass, speed
6. increases
7. Kinetic energy = ! Mass ! Speed 2
8. quadruple
9. Potential energy is stored energy that results from the position or shape of an object.
10. elastic potential energy
11. gravitational potential energy
12. Gravitational potential energy = Weight ! Height
13. true
14. potential and kinetic
15. Add together the potential and kinetic energies of an object.
16. joule
17. potential energy
18. Its kinetic energy increases and its potential energy decreases.
19. 12 -- 12--
Maximum
kinetic energy
Maximum
potential
energy
Maximum
potential
energy
Acceleration =
Final velocity
"
______I_n_i_ti_a_l_ v_e_l_o_c_it_y_
Time
Acceleration =
Final velocity
"
______I_n_i_ti_a_l_ v_e_l_o_c_it_y_
ANSWER KEY
Grade 8 Physical Science
20. When one form of energy is transformed into another, no energy is destroyed in the process.
Chapter 9 Motion and Energy
Chapter 9 Level B
Describing Motion
1. a. motion
b. reference point
2. true
3. a. displacement
b. distance
4. true
Speed and Velocity
1. a. Distance
b. Time
2. false
3. a
4. velocity
5. b, c
6. a, c
7. slope
8. b
Acceleration
1. acceleration
2. a, b, c
3. false
4. a. Final velocity
b. Time
5. true
6. a. 8 m/s
b. 2 m/s
c. 3 s
7. c
8. a. Speed-vs-time
b. Distance-vs-time
9. a. Graph B
b. Graph A
c. Graph A
Energy
1. kinetic energy
2. a. Mass
b. Speed (either order)
3. potential energy
4. a. elastic potential
b. gravitational potential
5. false
6. b
7. A
8. C
9. false