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

G-Givens:E-Base formula/rule:S-Answer: S-Work: Diagrams: 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 U-Unknown: S av Duncan Phillips AMCHS ‘07 ‘O6 State Gold Medal 1600 m S av = d t S av = d t = 8 m/s 8 m/s msms

Example 2: According to the World Disk Federation, on April 8,2000 Jennifer Griffin threw a Frisbee for a distance of 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:E-Base formula/rule:S-Answer: S-Work: Diagrams: S av = 13.0 m/s d = m U-Unknown t = ? S av = d t t = d S av = m 13.0 m/s = = 10.7 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:E:Baseformula/rule:S-Answer: S: Work: Diagrams: V o = 0 m/s a = 8 m/s 2 t = 5 s U:V f = ? V f = 0m/s + (8m/s 2 )(5s) V f = 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:E:Baseformula/ rule: S-Answer: S- Work: Diagrams: v o = 15 km/h = 4.17 m/s v f = 60 km/h = 16.7 m/s t = 20 s Unknown = a m/s s = m/s 2 = 0.63 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:Base formula/rule:Answer: Work: Diagrams: Vo = 20 m/s Vf = 0 m/s a = - 3 m/s/s t =? t = V f – V o a t = 0 – 20 m/s -3 m/s 2 t = s 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 = 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 9.3m/s when she is 8m from 2 nd base and 7.5m/s when she is 5m from 2 nd base 0.4s later. What is her acceleration over that 3m 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 = 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