Transfer of Forces Classwork

Transcription

1 Transfer of Forces Classwork 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.

2 Transfer of Forces Homework 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

3 Law of Gravitation Classwork 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?

4 13. Sketch a graph of Force of Gravitation (N) vs. Distance of Separation (m) between any two objects. Explain what the graph shows.

5 Law of Gravitation Homework 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.

6 18. If the mass of Earth doubled, your weight would. Explain. 19. If the Earth s radius doubled, your weight would. Explain.

7 Interaction between Electric Charges Classwork 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.

8 Interaction between Electric Charges Homework 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?

9 Forces between Charges Classwork 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.

10 Forces between Charges Homework 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.

11 Electric Fields Classwork 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.

12 Electric Fields Homework 40. Draw the field that exists between the two oppositely charged parallel plates shown below. A -q +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?

13 Magnetism Classwork 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.

14 Magnetism Homework 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?

15 Magnetic Fields Classwork 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.

16 Magnetic Fields Homework 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.

17 Electromagnetic Interactions Classwork 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.

18 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.

19 Electromagnetic Interactions Homework 8 th 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?

20 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 Equal 23. More electrons than protons 24. More protons than electrons

21 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

22 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.