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Force and Motion

Force and Motion. 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? Homework: Balanced Forces Worksheet. Vocabulary Updates.

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Force and Motion

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  1. Force and Motion

  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? • Homework: Balanced Forces Worksheet

  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. • Pass the description to the other person at your table (do not write the object name). • 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: Relative Motion and Frame of Reference • Review homework • Videos • Discussion • Read pp 31-33 and answer ??

  7. 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

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

  9. 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!!

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

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

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

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

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

  15. Galileo

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

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

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

  19. Friction and Inertia

  20. 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.

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

  22. Objects At Rest

  23. Objects in Motion

  24. 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.

  25. 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

  26. 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

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

  28. Mass – A Measure of Inertia

  29. Mass is not volume

  30. Mass is not volume

  31. Mass is not weight

  32. Measuring Mass and Force

  33. Effects of Forces on Speed

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