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MECHANICS

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  1. MECHANICS

  2. Motion Chapter 1 Notes

  3. What is a RATE? • A rate tells how fast something happens. • Some rates that we will use to describe motion are: • Speed • Velocity • Acceleration

  4. What is Motion??? • A change in position.

  5. What is speed? • Rate of Change in Position. • “Rate of Motion” • Types of Speed • Instantaneous • Constant • Average

  6. Speed Formula speed = the change in distance the change in time v = ∆ d ∆ t ∆ is the Greek letter DELTA. In science this means CHANGE.

  7. Speed Units • m/s • km/s • m/h • km/h • When you read the first unit, you say meters “PER” second. • Do not write mps

  8. Instantaneous Speed • The rate of motion at a given instant. • A speedometer in a car shows the instantaneous speed of the car.

  9. Average Speed • On a trip from Chicago to Texas could you stay the same speed? • You could get an average of all the speeds during the trip.

  10. How do we calculate average speed? • The total distance of the trip divided by the total time of travel.

  11. Constant Speed • A speed that does not change over a period of time. • Cruise Control in a car.

  12. Any questions about the Section Review Questions? • Page 14

  13. Speed is Relative! • What does it mean when we say that a car moves at a rate of 80 km/h? • What do we mean that it is relative to? • Unless the problem says something else, the motion that we discuss is ALWAYS relative to Earth.

  14. Everything is in constant motion • Do you agree?

  15. Galileo • Why did he have such difficulty spreading his findings?

  16. Velocity Notes 1.2

  17. What is Velocity? • Describes the motionand the direction. • Even if speed remains the same, if the direction changes then the velocity has changed.

  18. Any questions about the Section Review Questions? • Page 16

  19. VELOCITY VECTORS • VECTOR: An arrow drawn to scale that represents the magnitude and direction of a given velocity. 10m/s left 5m/s rt

  20. RESULTANT: The single vector that results when two vectors are combined. 10m/s left 5m/s rt 5m/s left

  21. Turn to the question on Page 17: • A motor boat is moving 10 km/h relative to the water. If the boat travels in a river that flows at 10km/h, what is the velocity relative to the shore when it heads directly up stream? • When it heads directly downstream?

  22. Now, let’s Check Your Understanding!

  23. Calculating Average Speed / Velocity • d= distance • v= speed / velocity • t= time

  24. Follow the steps to solve an equation. • Problem: You walk 5 meters in 3 seconds. What is your velocity? • Step 1: Write what you know. d = 5 meters t = 3 seconds v = ? • Step 2: Write the formula you will use. v = d / t • Step 3: Put the numbers in for the variables that you know. v = 5 meters 3 seconds • Step 4: Do the math. v = 1.6667meters/seconds = 1.7m/s Your velocity is 1.7 meters per second.

  25. Equations for Speed and Velocity • v = d / t • d = v  t • t = d / v

  26. Sample Speed / Velocity Problems • A car travels a distance of 16 m in 1.8 seconds. What is it’s speed? • d = 16 m • t = 1.8 s • v = ? • v = d/t v = 16m / 1.8s v = 8.89 m/s

  27. Sample Speed / Velocity Problems • Sound travels at a speed of 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for the sound to reach you? • v = 330m/s • d = 1km • t = ? • t = d/v t = 1km / 330m/s t = 1000m / 330m/s t = 3.03 s

  28. Your Turn! • Complete the worksheet.

  29. Acceleration Section 1.3

  30. What is Acceleration? • The rate of change of velocity. • Car commercial  0 to 60 mph in 10 seconds. • Speeding up • The amount of change of velocity in a time interval.

  31. How do you measure a change? • The water was at 50m and it rose to 100m. What is the change? • We started at 9:00am and the class was over at 11:00am. What is the change? • The dog grew from 8 lbs to 15 lbs. What is the change? • We had 20 gallons, and now we have 5. What is the change?

  32. How to Calculate Acceleration?  means “change in”

  33. How do you calculate Δv? • The change in velocity = the final velocity – the initial velocity. Δv = vf – vi • You are stopped at a red light. When it turns green, you speed up to 45m/s. What is your change in velocity? vi = 0m/s vf = 45m/s Δv = ? Δv = vf-vi = 45m/s- 0m/s = 45m/s

  34. Acceleration Units • velocity unit/ time unit • km/h/s • m/s/s • or m/s2

  35. What are some other ways to say that the car is accelerating?

  36. Any questions about the Section Review Questions? • Page 20

  37. What is negative acceleration? • Also known as DECELERATION. • The negative rate of change of velocity. • Slowing down. • The amount of negative change of velocity in a time interval.

  38. How does it feel? • When you accelerate? • When you decelerate?

  39. Look at Fig 1.10 on pg 21 • Which ball will hit the ground first? • Which ball accelerates the most? • Which ball will have the fastest speed at the end? A D B C

  40. What did Galileo find from the ramp experiment? • Steeper inclines = greater acceleration • All materials fall with the same acceleration. (when you can neglect air resistance)

  41. How will we use the acceleration formula to solve problems? • a = v / t • v = a X t • t =v / a

  42. Let’s Practice with some Problems • A car’s velocity changes from 0 m/s to 30 m/s in 10 seconds. Calculate the car’s average acceleration. • v = 30m/s • t = 10s • a = ? • a = v / t a = 30 m/s / 10s a = 3 m/s/s or 3 m/s2

  43. Practice Problems • A swimmer speeds up from 1.1 m/s to 1.3 m/s during the last 20 s of the workout. What is the acceleration during this interval? • v = 1.3 m/s – 1.1 m/s = 0.2m/s • t = 20s • a = ? • a = v / t a = 0.2 m/s / 20s a = 0.01 m/s/s or m/s2

  44. Let’s Review Speed! • http://www.unitedstreaming.com/

  45. Graphing Motion Review