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Force and Motion

Force and Motion. 8 th Grade Science Mrs. Howald. Today in Science: Explain that an unbalanced force acting on an object changes that object's speed and/or direction. . Main Idea: How have our ideas changed since the Greeks started studying motion? Log Updates: Log sheet #3

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Force and Motion

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  1. Force and Motion 8th Grade Science Mrs. Howald

  2. Today in Science: Explain that an unbalanced force acting on an object changes that object's speed and/or direction. • Main Idea: How have our ideas changed since the Greeks started studying motion? • Log Updates: • Log sheet #3 • Inertia power point notes • Homework: Reflection (above)

  3. Vocabulary Updates Force – a push or pull Friction – a contact force that opposes motion and occurs when a moving object rubs against a surface Mass – amount of matter that an object contains Inertia –tendency of an object to remain at rest or in motion until acted upon by an external force

  4. Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point. 10-14-08 Main Idea: When we describe the location of any object, it is necessary to refer to other objects in the same area. This is an example of a “reference point”.

  5. Where is it? • Describe the location of some object in the classroom. • Write your description on a piece of paper. • Give your description to another student (without the answer) • After receiving a description from another student, try to find the object described on another student’s paper—write your answer at the bottom of the page

  6. Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point. • Main Topic: What is the difference between distance and displacement? • Check understanding of reference points • Washer Activity • Discussion • Vocabulary Words Homework: distance and displacement worksheet – due tomorrow

  7. Describe how the change in the position (motion) of an object is always judged and described in comparison to a reference point. • Main Topic: Relative Motion and Frame of Reference • Review homework • Videos • Discussion • Read pp 31-33 and answer ??

  8. Relative Motion • http://www.youtube.com/watch?v=QBH71YgC1BA • http://www.youtube.com/watch?v=yPHoUbCNPX8 • http://www.youtube.com/watch?v=62yHCse9qDY • http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=140

  9. Reminder (Previous cycle):Distance and Displacement START FINISH Need to distinguish how long we traveled from how far away (and in what direction) we traveled.

  10. Distance and displacement • Distance and displacement are two quantities which may seem to mean the same thing, yet have distinctly different definitions and meanings.Distance refers to "how much ground an object has covered" during its motion. • Displacement refers to "how far out of place an object is"; it is the object's change in position. • http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1c.html

  11. Vocabulary • Position – the description of where an object is in space • Direction – the line or path along which an object moves

  12. Vocabulary • Frame of reference (reference point) – a stationary object against which motion is measured • Motion – the change in position of an object with respect to time • Relative Motion – the motion of one body relative to another. • Please add this word to your list!!

  13. Force and Motion -- Log Sheet Force and Motion Log Sheet Updates • October 14-23 Class Notes • Vocabulary Page • Distance and Displacement Worksheet • The Traveling Washer • 2.1 Review Worksheet • Race Car Lab Worksheet • Practice Worksheet -- Speed

  14. 8. Calculating average speed 9. Graphing Distance VS Time 10. Motion Graphs • Reflection #2 • Calculating speed, distance, and time

  15. Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. • Main Topic: Determining Speed • Lab Reports • Pop Quizzes • Race Car Lab • Discussion • Homework: Complete the Practice Worksheet -- Speed

  16. Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. • Main Topic: Constant Speed, Average Speed, Instantaneous Speed • Review data from yesterday – make graphs on the floor • Discuss speed and the unit of measure for speed • Review worksheet from yesterday – make corrections • Practice worksheet for constant speed graph • Vocabulary

  17. Spring 2005 Data Video 2

  18. Vocabulary • Speed – the distance an object moves in a certain time period speed = distance time • Constant Speed – Moving equally fast all the time.

  19. Average vs. Instantaneous speedAdd these words to your list • Average speed is the distance traveled divided by the time to travel. • Instantaneous speed is the average speed for infinitely small distances and times.

  20. Explain that motion describes the change in the position of an object (characterized by a speed and direction) as time changes. • Main Topic: Calculate Speed, Distance, or Time. • Daily Review • S/D/T relationship and formulas • Practice Problems • Vocabulary • Homework: Complete the other side of the Calculating Speed Worksheet – word problems for speed, distance and time. The last two are “extra credit”.

  21. Understanding Speed

  22. Acceleration and Deceleration (Negative Acceleration)

  23. http://www.online-stopwatch.com/full-screen-stopwatch/ • Main Topic: How forces affect motion • Check homework • Outline • Study Guide • Videos • Homework – quiz on Friday – review study guide.

  24. Vocabulary Velocity – the speed of an object in a particular direction Acceleration – a change in velocity • Motion – the change in position of an object with respect to time

  25. Aristotle and Motion • Idea that force causes motion goes back to the fourth century B.C.E. -- Greeks • Divided into two types: • Natural Motion • Violent Motion

  26. Aristotle and Motion • Natural Motion • Up or Down • Objects seek a natural resting place -- boulders/ground smoke/high • Circular motion is “natural” for the heavens. Planets and Stars revolve around Earth

  27. Aristotle and Motion • Natural Motion • Since they are natural, they are not caused by forces.

  28. Aristotle and Motion • Violent Motion • Imposed Motion – a push or a pull • External Cause • Objects in their natural resting places could not move without a push or a pull • If an object is moving “against its nature” then a force is responsible

  29. Ideas About Motion • These ideas were believed for over 2000 years.

  30. Copernicus 1473-1543 • First to say that the Earth moved around the Sun. • Worked in secret

  31. Galileo A force is necessary to keep an object moving

  32. Galileo • Force = any push or pull • Friction = the force that acts between materials that touch as they move past each other

  33. Galileo • Friction – if friction were absent, a moving object would need no force to stay in motion

  34. Galileo

  35. Galileo • If an object is moving, it is “natural” to keep moving. • Every object resists change to its state of motion.

  36. Galileo • Inertia – the property of a body to resist change

  37. Newton – 1642-1727 • Laws of Motion • The first law (law of inertia) is a restatement of Galileo’s idea.

  38. Friction and Inertia

  39. Newton – 1642-1727 • Newton’s First Law: • Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it.

  40. Newton – 1642-1727 • Simply put: • Things keep doing what they are already doing.

  41. Objects At Rest

  42. Objects in Motion

  43. In Review • Inertia gives us a completely different view of motion. • Ancients thought – continual forces were needed to keep something in motion • We now know that objects continue to move by themselves • Forces may be needed to overcome friction and set things into motion at first. • Once an object is moving in a force free environment, it will move in a straight line indefinitely.

  44. Mass – A Measure of Inertia • Kick and empty can and it moves • Kick a can filled with sand and it does not move as much • Kick a can filled with nails and you’ll have a sore foot • Inertia: • Can full of nails = most • Can full of sand = less • Empty can = least

  45. Mass – A Measure of Inertia • Kick and empty can and it moves • Kick a can filled with sand and it does not move as much • Kick a can filled with nails and you’ll have a sore foot • Inertia: • Can full of nails = most • Can full of sand = less • Empty can = least

  46. Mass – A Measure of Inertia • The amount of inertia an object has depends on its mass—the amount of material present in an object.

  47. Mass – A Measure of Inertia

  48. Mass is not volume

  49. Mass is not volume

  50. Mass is not weight

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