Acceleration Acceleration Acceleration is the measure of how

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 * Vi can also be written as Vo (original velocity)

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.

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

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? G-Givens: d = 200 m t = 25 s U-Unknown: Sav Diagrams: Duncan Phillips AMCHS ‘ 07 ‘O 6 State Gold Medal 1600 m E-Base formula/rule: S-Answer: 8 m/s Sav = d t S-Work: Sav = d t m s = 8 m/s

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? G-Givens: Sav = 13. 0 m/s d = 138. 56 m U-Unknown t = ? Diagrams: E-Base formula/rule: Sav = d t S-Work: t= d Sav S-Answer: = 10. 7 s = 138. 56 m = 10. 658 13. 0 m/s

Example 3: An object starts from rest with a constant acceleration of 8 m/s 2 along a straight line. Find the speed at the end of 5 s G: Vo = 0 m/s a = 8 m/s 2 t = 5 s U: Vf = ? Diagrams: E: Baseformula/rule: S-Answer: Vf = 40 m/s S: Work: Vf = 0 m/s + (8 m/s 2)(5 s) Vf = 40 m/s

Example 4: A truck's speed increases uniformly from 15 km/h to 60 km/h in 20 s. Determine the acceleration. G- Givens: vo = 15 km/h = 4. 17 m/s vf = 60 km/h = 16. 7 m/s t = 20 s E: Baseformula/ rule: S-Answer: = 0. 63 m/s 2 S- Work: Unknown = a m/s s Diagrams: = 0. 6265 m/s 2

Example 5: A bus moving at a speed of 20 m/s begins to slow at a constant rate of 3. 0 m/s 2. How long before it stops? Givens: Vo = 20 m/s Vf = 0 m/s t =? a = - 3 m/s/s Diagrams: Base formula/rule: Work: t = Vf – Vo a t = 0 – 20 m/s -3 m/s 2 t = 6. 6667 s Answer: t = 6. 67 s

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

PROBLEM SOLVING GUIDELINES • Make a list of given quantities (Data) • Convert units if needed (e. g mins 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

QUESTION: A baseball player sprints from 1 st base, to 2 nd base. If her velocity is 9. 3 m/s when she is 8 m from 2 nd base and 7. 5 m/s when she is 5 m from 2 nd base 0. 4 s later. What is her acceleration over that 3 m interval?

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

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 = x 100 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