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Chapter 11: Motion

Chapter 11: Motion. Section 1. Measuring Motion. Key I deas. What is frame of reference? What is the difference between speed and velocity? How do you calculate speed ?. Motion. Motion: change in position Frame of reference: something you can compare the motion of an object to

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Chapter 11: Motion

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Presentation Transcript

  1. Chapter 11: Motion

  2. Section 1 Measuring Motion

  3. Key Ideas • What is frame of reference? • What is the difference between speed and velocity? • How do you calculate speed?

  4. Motion • Motion: change in position • Frame of reference: something you can compare the motion of an object to • The trees in the picture can be used as reference points to describe the motion of the snowboarder

  5. Describing Motion • Directions: north, south, east, west, up, down • Distance: how far an object has moved

  6. Displacement • Motion and direction of motion • Ex: the student walked 12 blocks north to get to school • Yellow line = total distance • Black arrow = “displacement”

  7. Speed • how fast something is moving Speed = distance (in meters) time (in seconds) SI unit: m/s

  8. What is the speed of the galloping horse? • 200 meters in 10 seconds • Speed = 200m 10s • Speed = 20m/s • Note: “m/s” is read as “meters per second”

  9. Velocity • Speed with direction • Ex: the lion escaped from the zoo and is traveling at 2m/s north

  10. Constant Speed vs. Average Speed • If a train moves 67 meters every second, it has a constant speed of 67 m/s. • Most objects do not move at a constant speed (think about driving in your car) • My apartment is 20 miles away from school • It takes me half an hour to get here • My average speed is 20mi/.5hr = 40mi/hr • Am I traveling at 40mi/hr the whole time I am driving? (**stop lights!)

  11. Graphing Motion • Motion can be studied using a distance vs. time graph. • distance on the vertical (y) axis • Dependant variable • time on the horizontal (x) axis • Independent variable

  12. Speed = Slope • The slope of any distance vs. time graph gives the speed of the object. • Which cars are moving at a constant speed? • Which car is moving at the fastest speed? A B C

  13. Section 2 Acceleration

  14. Key Ideas • How do you calculate acceleration? • How do yougraph acceleration?

  15. Acceleration • A change in speed or direction • When an object slows down its acceleration is negative

  16. You can constantly accelerate while never speeding up or slowing down! • How…?

  17. Centripetal Acceleration • Circular motion • Examples: • The moon • A Ferris wheel • blades of a windmill

  18. Calculating Acceleration Means “change”

  19. Graphing Acceleration • You can find acceleration by making a speed vs. time graph • speed on the vertical (y) axis • time on the horizontal (x) axis • Slope = acceleration • positive slope means object is speeding up • negative slope means object is slowing down

  20. Which of the two graphs represents speed? Acceleration?

  21. Section 3 Motion and Force

  22. Key Ideas

  23. Force • Any action that can change the state of motion of an object • Three Fundamental Forces: • gravity • electromagneticforce • strong nuclear force

  24. strong nuclear force • holds together the protons and neutrons in the nuclei of atoms • strongest of all the forces • Works over the shortest distance (distances the size of an atomic nucleus)

  25. electromagnetic force • the attraction between opposite charges and repulsion between like charges • is about 1/100 the strength of the strong force • acts over longer distances

  26. gravitational force • the attraction between two objects • much weaker than the electromagnetic force • Acts over long distances

  27. Contact Forces vs. Field Forces • Contact forces: objects touch • Ex: • If you push a cart, the cart moves. • When you catch a ball, it stops moving. • Field forces: objects do not touch • Ex: • gravity • repulsion between two north poles of a magnet

  28. Net forces • The total force acting on an object • An object will accelerate in the direction of the net force

  29. The Force of Friction • opposes motion between two surfaces that are in contact • When two surfaces are touching, the surfaces “stick” to each other • Result of the electromagnetic force

  30. Types of Friction • Static friction: friction between still objects • Kinetic friction: friction between moving objects • Static friction is greater than kinetic friction

  31. Types of Kinetic Friction • Sliding friction: when objects slide past each other • Rolling friction: when round objects roll over a flat surface • Sliding friction is usually greater than rolling friction.

  32. We Need Friction! • For the tires of a car to push against the ground and move the car forward • For brakes to be able to stop your car • For your pencil to be able to leave a mark on your paper • To be able to walk without slipping and falling

  33. Car Breaks Rely on Friction • Two types of brakes are typically found in modern cars • Disc brakes: usually used to stop the front wheels of a car • Drum breaks • For brakes to work, the system requires leverage, hydraulic force and friction.

  34. Unwanted Friction Can Be Lowered • Non-stick pans • Oil on bike chains • Air hockey tables • Motor oil

  35. Helpful Friction Can Be Increased • Scattering sand on icy roads prevents cars from sliding • batting gloves help baseball players get a better grip on the bat • Paper weights prevent papers from blowing away

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