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Acceleration

Acceleration. Acceleration. Acceleration is the measure of how fast something speeds up or slows down. SI units for Acceleration =m/s 2. Acceleration. When velocity of an object changes An object speeds up or slows down An object turns (changes direction). Equation for Acceleration.

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Acceleration

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  1. Acceleration

  2. Acceleration • Acceleration is the measure of how fast something speeds up or slows down. • SI units for Acceleration =m/s2

  3. Acceleration • When velocity of an object changes • An object speeds up or slows down • An object turns (changes direction)

  4. Equation for Acceleration *Vi can also be written as Vo  (original velocity)

  5. Acceleration • Acceleration is a vector because it has magnitude and direction. • If the final velocity is greater than the initial velocity then the ΔV (acceleration) will be positive. • If the final velocity is less than the initial velocity then the ΔV (acceleration) will be negative.

  6. A positive acceleration means an increase in velocity; a negative acceleration usually means a decrease in velocity (deceleration). NB!! Negative acceleration is in OPPOSITE direction of the velocity

  7. Example 1: A runner makes one lap around a 200 m track in a time of 25 s. What is the runner's average speed? d = 200 m t = 25 s 8 m/s Sav = d t U-Unknown: Sav Sav = d t = 8 m/s m s Duncan Phillips AMCHS ‘07 ‘O6 State Gold Medal 1600 m

  8. Example 2: According to the World Disk Federation, on April 8,2000 Jennifer Griffin threw a Frisbee for a distance of 138.56 m to capture the woman’s record. If the Frisbee was thrown horizontally with a speed of 13.0 m/s, how long did the Frisbee remain aloft? Sav = d t = 10.7 s Sav = 13.0 m/s d = 138.56 m U-Unknown t = ? t= d Sav = 138.56 m 13.0 m/s = 10.658

  9. Example 3: An object starts from rest with a constant acceleration of 8 m/s2 along a straight line. Find the speed at the end of 5 s Vo= 0 m/s a = 8 m/s2 t = 5 s Vf = 40 m/s U:Vf = ? Vf = 0m/s + (8m/s2)(5s) Vf = 40 m/s

  10. Example 4: A truck's speed increases uniformly from 15 km/h to 60 km/h in 20 s. Determine the acceleration. vo= 15 km/h = 4.17 m/s vf = 60 km/h = 16.7 m/s t = 20 s = 0.63 m/s2 Unknown = a m/s s =0.6265 m/s2

  11. Example 5: A bus moving at a speed of 20 m/s begins to slow at a constant rate of 3.0 m/s2. How long before it stops? t = 6.67 s Vo = 20 m/s Vf = 0 m/s a = - 3 m/s/s t =? t = Vf – Vo a t = 0 – 20 m/s -3 m/s2 t = 6.6667 s

  12. Practice Sakhile and Matthew walk eastward with a speed of 0.98 m/s. If it takes them 34 min to walk to the store, how far have they walked? • Given: Speed = 0.98 m/s, time = 34 minutes (2040 sec) • Unknown: How far? Distance = ? • Equation: Speed = distance / time v = d/t • rearrange for distance d = vt • Substitute/Solve: d = (.98 m/s) (2040 s) d = 1999.2 meters

  13. PROBLEM SOLVING GUIDELINES • Make a list of given quantities (Data) • Convert units if needed (e.gmins sec) • Make a drawing if necessary • Identify what is to be determined • Determine the equation needed • Always solve the equation for the unknown and be consistent with units • Check that the answer seems reasonable

  14. QUESTION: A baseball player sprints from 1st base, to 2nd base. If her velocity is 9.3m/s when she is 8m from 2nd base and 7.5m/s when she is 5m from 2nd base 0.4s later. What is her acceleration over that 3m interval?

  15. ANSWER: Acceleration = (vf – vi) t = (7.5 – 9.3) m/s 0.4 s = -1.8 m/s 0.4 s = -4.5 m/s

  16. Conversions: • Min  Sec = x 60 • Sec  min = ÷ 60 • Min  hour = ÷ 60 • Hour  min = x 60 • M  km = ÷1000 • Km  m = x 1000 • Mm  cm = ÷10 • Cm  mm = x 10 • Cm  m = ÷ 100 • M  cm = x100 • If you are converting to a BIGGER unit  the number will decrease/ get smaller • If you are converting to a SMALLER unit  the number will get bigger

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