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# Chapter 5rr

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### Chapter 5rr

1. 1. Matter in Motion Chapter 5
2. 2. Measuring Motion <ul><li>The object that appears to stay in place is a reference point . </li></ul><ul><li>When the object changes position over time when compared with a reference point, the object is in motion. </li></ul><ul><li>When an object is in motion describe the objects direction by using north, south, east, west, up or down. </li></ul>
3. 3. Speed Depends on….. <ul><li>The rate at which objects moves is its speed. </li></ul><ul><li>Speed depends on distance traveled and the time it takes to travel that distance. </li></ul><ul><li>The SI unit for speed is meters per second (m/s). </li></ul><ul><li>Most objects don’t travel at a constant speed so we use an average speed. </li></ul><ul><li>The average speed is calculated by dividing total distance by total time. </li></ul>
4. 4. Lil….Speed…. Practice <ul><li>A car travels the 180 miles from Seattle to Portland at a constant 60 mph, then turns around and returns to Seattle at a constant 90 mph.  What is the average speed of the car during this trip? </li></ul>
5. 5. Answer <ul><li>Solution: </li></ul><ul><li>The answer is not 75 mph as you might mistakenly think.  The car takes 3 hours going to Portland and 2 hours returning so it spends a total of 5 hours traveling 360 miles for an average speed of 360/5 = 72 mph.  </li></ul><ul><li>If this seems odd, remember that the problem has the car traveling at two different speeds over the same distance , which is not the same as traveling at two different speeds for the same amount of time .  In this latter case you can indeed just average the two speeds to find the average speed.  But in our case, since the car spent a longer amount of time traveling at the slower speed, the average speed is closer to 60 mph than to 90 mph </li></ul>
6. 6. Velocity: Direction Matters <ul><li>Velocity is speed in a given direction. </li></ul><ul><li>Velocity gives distance, time, and the direction of travel. </li></ul><ul><li>Constant Velocity is always along a straight line. </li></ul><ul><li>Velocity changes if speed or direction changes. </li></ul><ul><li>Resultant Velocity is the combination of two or more velocities. </li></ul>
7. 8. <ul><li>Which car or cars (red, green, and/or blue) </li></ul><ul><li>are undergoing an acceleration? </li></ul><ul><li>Study each car individually in order to </li></ul><ul><li>determine the answer. </li></ul><ul><li>                                                                                   </li></ul>
8. 9. Acceleration <ul><li>The rate at which velocity changes is acceleration </li></ul><ul><li>The faster velocity changes, the greater the acceleration. </li></ul><ul><li>Acceleration=(final velocity)-(starting velocity)/time it takes to change velocity </li></ul><ul><li>Velocity is expressed meters per second (m/s) and time is expressed in seconds (s) </li></ul><ul><li>How is acceleration expressed? </li></ul>
9. 10. Examples of Acceleration <ul><li>Positive Acceleration: velocity increases </li></ul><ul><li>Negative Acceleration (Deceleration): velocity decreases </li></ul><ul><li>Since Velocity has direction, the velocity will change if the direction changes. </li></ul><ul><li>A change in direction is acceleration, even if there is no change in speed. </li></ul>
10. 11. At what point does the car stop accelerating?
11. 12. <ul><li>Which car or cars (red, green, and/or blue) </li></ul><ul><li>are undergoing an acceleration? </li></ul><ul><li>Study each car individually in order to </li></ul><ul><li>determine the answer. </li></ul><ul><li>                                                                                   </li></ul>
12. 13. <ul><li>2. Consider the position-time graph at the right. </li></ul><ul><li>Each one of the three lines on the position-time graph corresponds to the motion of one of the three cars. </li></ul><ul><li>Match the appropriate line to the particular color of car </li></ul>
13. 14. Answers <ul><li>13. Goldie Goldfish, a speed swimmer, loves to race around the park’s pond, which is 0.5 miles around. If she </li></ul><ul><li>can swim 20 laps around the track in 2 hours, what is her average speed? </li></ul><ul><li>20 x 0.5 = 10 miles ÷ 2 hours = 5 mph </li></ul><ul><li>14. It takes Stu, a slimy slug, 20 minutes to travel from his favorite bush to the local trash can (a trip of 30 </li></ul><ul><li>meters), how far can he travel in 1 hour (60 minutes)? </li></ul><ul><li>30 ÷ 20 = 1.5 m/min x 60 min = 90 m </li></ul><ul><li>15. At exactly 2:00 pm, Speedy the Snail crawls onto a meter stick at the 10 cm mark. If he reaches the 65 cm </li></ul><ul><li>mark at exactly 2:10 pm, what is his speed? </li></ul><ul><li>65 cm - 10 cm = 55 cm ÷ 10 min = 5.5 cm/min </li></ul><ul><li>16. If it takes Leaping Louie 5 minutes to jump 3 blocks, how long will it take for him to jump 15 blocks? </li></ul><ul><li>3 blocks ÷ 5 min = 0.6 blocks/min 15 blocks ÷ 0.6 blocks/min = 25 min </li></ul><ul><li>17. If Bert the Bat travels eastward at 40 mph with a tail wind of 6 mph, what is his actual speed? </li></ul><ul><li>40 mph + 6 mph = 46 mph </li></ul>
14. 15. Which of Newton’s Law http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/newtlaws/cci.html Newton’s first Law
15. 16. Review of Newton Laws
16. 17. Review of Newton Laws
17. 18. 2 nd Law <ul><li>Newton's second law of motion pertains to the behavior of objects for which all existing forces are not balanced. The second law states that the acceleration of an object is dependent upon two variables – the net force acting upon the object and the mass of the object. </li></ul>Force=Mass x Acceleration
18. 19. Third Law of Motion <ul><li>While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus? </li></ul>Trick Question! Each force is the same size. For every action, there is an equal ... (equal!). The fact that the firefly splatters only means that with its smaller mass, it is less able to withstand the larger acceleration resulting from the interaction. Besides, fireflies have guts and bug guts have a tendency to be splatterable . Windshields don't have guts. There you have it.
19. 20. 4. In the top picture (below), Kent Budgett is pulling upon a rope which is attached to a wall. In the bottom picture, the Kent is pulling upon a rope which is attached to an elephant. In each case, the force scale reads 500 Newtons. Kent is pulling ... <ul><li>with more force when the rope is attached to the wall. </li></ul><ul><li>b. with more force when the rope is attached to the elephant. </li></ul><ul><li>c. the same force in each case. </li></ul>Answer C