Transfer of Forces Classwork
Name: __________________________
8th Grade PSI
1. Describe what a force is.
2. List at least four forces that are observed in nature.
3. How are forces transferred between two objects if they are not in contact?
4. Describe what happens to an object when there are unbalanced forces acting on
it.
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Transfer of Forces Homework
Name: __________________________
8th Grade PSI
5. Describe the difference between contact forces and field forces.
6. Define the term “Field of Force” as it applies in the area of physics.
7. List two of examples of each and justify your answer:
a. Field force
b. Contact force
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Law of Gravitation Classwork
Name: __________________________
8th Grade PSI
8. Write a statement that summarizes Newton’s Universal Law of Gravitation.
9. What is meant by the term “Universal Law”?
10. What two factors affect the force of gravitation acting between two objects?
11. Describe the mathematical relationship between an object’s mass, and the force
of gravitation exerted by that mass.
12. What happens to the force of gravitation between two objects as they get further
apart?
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13. Sketch a graph of Force of Gravitation (N) vs. Distance of Separation (m)
between any two objects. Explain what the graph shows.
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Law of Gravitation Homework
Name: __________________________
8th Grade PSI
14. In your own words, explain why we can’t feel the force of gravitation exerted by
objects such as people.
15. Draw a sketch of the gravitational field surrounding Earth, and explain why the
field lines diverge (spread out) as we move away from the surface of the planet.
16. Explain why the field lines point inward toward a mass when we draw a
gravitational field line diagram around an object.
17. Explain why the force of gravitation for Jupiter is greater than the force of
gravitation for the Moon.
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18. If the mass of Earth doubled, your weight would _________________. Explain.
19. If the Earth’s radius doubled, your weight would _______________. Explain.
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Interaction between Electric
Charges Classwork
Name: __________________________
8th Grade PSI
20. Define electric charge and list the two types of charge.
21. What are the three subatomic particles and their charges?
22. Explain the balance of electrons and protons in a neutral object.
23. Explain the balance of electrons and protons in a negatively charged object.
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Interaction between Electric
Charges Homework
Name: __________________________
8th Grade PSI
24. Explain the balance of electrons and protons in a positively charged object.
25. A charged balloon has a mixture of charge including +100 Coulombs and -200
Coulombs (Remember that Coulombs is the unit for electric charge). What is the
overall charge of the balloon? Explain your answer.
26. Who was the person who first used the terms “positive and negative” when
referring to electricity?
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Forces between Charges
Classwork
Name: __________________________
8th Grade PSI
27. What causes static cling?
28. Define Coulomb’s Law.
29. Explain what happens when like charges are near each other. What force do
they exert on each other?
30. Explain what happens when unlike charges are near each other.
31. Two electrically charged objects are brought near each other and then released.
The objects stick to one another. Describe the possible charge of each object.
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Forces between Charges
Homework
Name: __________________________
8th Grade PSI
32. What type of force acts between neutrally charged particles?
33. As charge increases, what is the effect on the electric force between those
charges? Explain.
34. As charge decreases, what happens to the force between two objects? Explain.
35. Sketch a graph of Electric Force (N) vs. Distance of Separation (m) between any
two charged objects. Explain what the graph shows.
36. Differentiate between Newton’s Law of Gravitation and Coulomb’s Law by
drawing a Venn Diagram to show their similarities and their differences.
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Electric Fields Classwork
Name: __________________________
8th Grade PSI
37. Draw the electric field lines that exist between two unlike charges.
38. Explain how the electric field lines that exist between two like charges would
differ from what you drew above.
39. Write the rules for drawing electric field lines.
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Electric Fields Homework
Name: __________________________
8th Grade PSI
40. Draw the field that exists between the two oppositely charged parallel plates
shown below.
-q
A
+q
B
41. Compare the strength of the electric field at location A and location B.
42. What is the electric field around a neutrally charged object?
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Magnetism Classwork
Name: __________________________
8th Grade PSI
43. What is magnetism?
44. Explain William Gilbert’s idea about the Earth.
45. What is a magnetic domain?
46. Compare the orientation of magnetic domains in a) magnetized substances, and
b) un-magnetized substances.
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Magnetism Homework
Name: __________________________
8th Grade PSI
47. Compare and contrast a temporary magnet and a permanent magnet.
48. What are the three ferromagnetic substances?
49. Draw a sketch with labels of a basic electromagnet.
50. What happens to the magnetism produced by an electromagnet when the
electrical current is removed?
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Magnetic Fields Classwork
Name: __________________________
8th Grade PSI
51. Sketch the magnetic field lines around a simple bar magnet. Make sure to label
the poles.
52. Explain how your drawing obeys the three basic rules for magnetic field lines.
53. Explain the forces exerted between a) like magnetic poles, and b) unlike
magnetic poles.
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Magnetic Fields Homework
Name: __________________________
8th Grade PSI
54. Compare the field shapes between like charges and like magnetic poles. Explain
why they look the same.
55. Explain how a magnetic compass works with the Earth’s magnetic field.
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Electromagnetic Interactions
Classwork
Name: __________________________
8th Grade PSI
56. Describe the contributions of Hans Christian Oersted to our understanding of
magnetism and electricity.
57. Draw the magnetic field around the straight wire carrying a current shown below.
The direction of the electric current is shown by the arrow.
58. Draw the magnetic field around the straight wire carrying a current shown below.
The direction of the electric current is shown by the arrow.
C
B
A
59. Compare the strength of the magnetic field at locations A, B and C. Justify your
answer.
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60. What happens to the strength of a magnetic field around a wire when current is
increased? Decreased?
61. Draw the magnetic field around the coil shown below. There is a current in the
coil and the direction is indicated by the arrows.
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Electromagnetic Interactions
Homework
Name: __________________________
8th grade PSI
62. Describe how to use the left hand rule.
63. Define induction.
64. You have a bar magnet, a looped wire and a light bulb but no battery. Describe
two different ways you can get the light bulb to light.
65. Why is the relationship between electricity and magnetism so important to
society?
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Answer Key
1. A force is a push or a pull.
2. Gravity, friction, electric force, and magnetism
3. Through force fields
4. The object accelerates
5. Contact forces require direct contact between objects while field forces are
exerted without touch through space.
6. Field of force- a force exerted through empty space
7. Answers will vary
a. Electricity, gravity, magnetism (charges, masses and magnets do not need
to touch in order to exert a force. They exert a force through empty space)
b. Friction (objects have to touch and slide against each other for frictional
forces to occur) and applied force (objects must be in contact for applied
forces to push/pull on an object, for example a person must touch a box to
move it).
8. Gravitational forces exist between masses and decrease as the distance
between masses increases.
9. Always true
10. Mass & distance of separation
11. Mass- directly proportional, distance- inversely proportional
12. Decreases exponentially
13. Graph should show force decreasing exponentially as distance increases and
explain this in words as well.
14. People have a small mass, so they exert small gravitational force compared to
the Earth, which is huge.
15. See presentation slide 39. Gravitational field lines should be pointing inwards
towards Earth (straight lines). They are more spread out the further from Earth
because gravitation is inversely proportional to distance squared meaning the
force is weaker the further from Earth an object is.
16. Attraction
17. Jupiter has more mass.
18. Double. Directly proportional
19. Be reduced. Inversely proportional (It would be ¼ of the original due to the
inverse square law)
20. Physical property of matter that allows it to feel an electric force when near other
electrically charged matter; Positive and negative
21. Protons +, electrons -, and neutrons 0
22. Equal
23. More electrons than protons
24. More protons than electrons
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25. -100 Coulombs. There are 100 more Coulombs of negative charge than positive
charge so the object has a net negative charge.
26. Ben Franklin
27. Electrical attraction between two objects.
28. Coulomb’s law describes how the strength of electric forces exerted between
charges changes due to the amount of charge and distance between charges.
Like- repel, unlike-attract
29. They repel each other. Repulsive electric force.
30. They attract each other. Attractive electric force.
31. They have opposite charges because they are attracted to each other. One must
have a negative net charge while the other has a net positive charge.
32. No force
33. Increases; directly proportional
34. Decreases; directly proportional
35. Graph should show electric force decreasing exponentially as the distance
between charges increase. Students should explain this in words as well.
36. Similarities-inverse square law, attraction force; Newton’s Law of Gravitationforce between masses, attraction force only; Coulomb’s Law-Repulsion force
(and attraction), force between charges.
37. See slide 72; Electric field lines should be coming out of the positive charge and
going into the negative charge.
38. Like charges repel. So in between the two charges there would be less electric
field lines and more space.
39. Exit +, enter -, never cross, closer lines = stronger field
40. Looks similar to slide 73 but electric field lines point in the opposite direction;
Field lines leave the positive plate and enter the negative plate. Electric fields
lines are equally space and parallel to each other between the charged plates.
41. They are equal.
42. None
43. Property of matter that causes magnetic forces due to electricity in motion
44. Earth is a giant magnet.
45. Microscopic magnetic region
46. A) magnetized- domains aligned, b) unmagnified – domains randomized
47. Temporary loses magnetism permanent holds it.
48. Iron,nickel,colbalt
49. Sketch should include a soft metal core surrounded by wire. The wire should be
connected to a battery.
50. Lost
51. See slide 101; lines go out from the North pole and into the South pole
52. Exit north, enter south, never cross, closer lines = stronger field
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53. Like- repel, unlike- attract
54. They look similar because like charges and like poles repel so lines are fewer in
between the charges/poles.
55. The magnetic north of the compass aligns with the geographic north of Earth.
That is because the geographic north of Earth is actually Earth’s magnetic south
(unlike poles attract). This allows people to determine which way is geographic
north and which is geographic south.
56. Electrical current causes magnetism.
57. Magnetic field is going into the page below the wire and out of the page above
the wire.
58. Magnetic field is going into the page to the right of the wire and out of the page to
the left of the wire.
59. A=C >B; Due to proximity to wire.
60. Increased current= stronger magnetic force/field, decreased current= weaker
magnetic force/field.
61. Use left hand rule; North pole is top, South pole is bottom. Magnetic field lines
therefore go out of the top of the nail and into the bottom.
62. Fingers are coiled/wrapped in direction of current in coils and thumb points in
direction of magnetic North pole that is induced.
63. Electricity causes magnetism and vice versa.
64. Force the bar magnet into the coil; pass the loop over the stationary bar magnet.
65. We use it to produce power and for communication.
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