# PCHOdi Acceleration and Average Speed ```Name Coy
Period:
| Acceleration and Average Speed
| Acceleration |
Acceleration 1s how fast
you change speed OR
how much the speed
changed in a certain
amount of time.
AV «— Change of Speed
(in meters/sec)
AT —#—— Change of Time
(in seconds)
Acceleration
(in meter/sec?)
Speed equal change of distance
divided by change of time.
АМ = V:- Y; АТ = T, - Ty
Ch. 2:1
a = AS/AT, not a = S/T,
Why? If a car is traveling at
60 m/s for 20 sec,
5 = 60 m/s, but AS = 0 m/s.
No change of speed:
no acceleration.
— Example:
Calculate Acceleration
Step 1: Variables
Ex. A plane starts at rest and ends
up going 200 m/s in 10 secs.
Calculate acceleration.
Step 2: Find AS Step 3: Formula
Step 4: Solve
S, = 0 m/s (“starts ar rest”)
a = (200 m/sy(10 s)
= 20 m/s*
S2 = 200 m/s А5 = \$ - 5, a= AS/AT
AT = 10 seconds = 200 - 0 = 200 m/s
a=?
Example: Ex. A race car starts at 400 m/s and Deceleration means an
Calculate Deceleratior : then stops in 20 seconds.
Calculate the car's acceleration.
Step 1: Variables
Step 2: Find AS Step 3: Formula
object is slowing down and
has a negative sign.
Step 4: Solve
a = (-400 m/s)/(20 s)
= -20 m/s?
S1= 400 m/s |
S,= 0 m/s (“then stops”) 0 “don 2 mis a= AS/AT
AT = 20 seconds Mn = 5 pr
а=? NOTICE NEGATIVE AS Negative
sign means deceleration.
| | Average Speed | | Speed vs. Velocity
& = Déotal Speed is a Scalar
ave = a .
Total Velocity isa Vector
Ex. A person walks 4 miles in 2 hours, then stops for
an hour for lunch. After lunch they walk 8 miles in
3 hours. Calculate the person’s average speed.
Distance Time
4 miles 2 hours
oT 0 miles 1 hour -
Careful—distance 15
O miles because
“stops ... for lunch”
8 miles 3 hours
| TOTALS: 12 miles | 6 hours
| Save — Diotat Total
= 12 mi/6 sec
= 2 mph
cstephenmurray.com
Speed has no direction; Scalars have no direction.
Velocity has direction; Vectors have direction.
A person walks 4 m/s—speed (no direction).
A person walks 2 m/s north— velocity (direction is given).
A car drives 60 mph toward Dallas—velocity.
A car drives 30 mph—speed.
A 14 newton force pull 30° left of north—yector. |
A boat is pulled by a 53 newton force—scalar.
Vectors have magnitude and direction.
Velocity is a vector with magnitude and direction.
speed vs. time graphs; Ch. 2:1
E =H LH and dvectrom
E Speed (S) ar Velocity (Y) Scalar (S) or Vector (V) Match the variables with quantities,
Vv A bike goes 25 m/s toward \/ 40 mph toward Dallas. la=_ FM / \$ & | 23 kilograms
main street |
— ил (5
| G A 25N force pulls on a 250rv=_23 mls 23 sec
> A person walks 4 mph. Wagon. 3.т= _# 3 La 3 m/s?
—\$ A plane flies 200 m/s. \/__10 meters up the bill 4.D 3 dl 23 meters/sec
. | | s.F=_23 M 23 meters
М A bird flies 100 mph due S 12 meter per sec”. 6.T= 23 Sw 23 newtons
south. o
A person starts running from 2 m/s to 6 m/s in 2 seconds. A plane stops from 250 mph in 25 seconds.
Calculate the person’s acceleration. | . Calculate the planes acceleration.
Variables: Solve: L-2 Variables: Solve: 6 - 250
Vi = 2/6 K= — Vi= 2S0mp А =
Из = г. / a | y ==
- 6 ws A Vi: O > 250
T= э се | #4 T=>25 Ses A = Ze
Formula: Zz | Formula: |
A EX | A-2m/ ja | A 710 0
TT T mPh/S
SE A guy bikes 13 miles in 1 hour, then rests for an hour. A dragster's top acceleration is 60 m/s”.
Ts Then he bikes 25 in 2 hours. If it accelerates for 3 seconds from the
What was his average speed for the trip? starting line, how fast will it be going?
Variables: | Solve: ol Variables: Solve: y, |
| - == но
d = о“ 5 = Om iz O m/<
2-— 2= 186 M/S
+ = Ч he | qi += 3 eC
Formula: | 0 I Formula:
S = a ‚ Р = A + +V,
+
Speed vs. Time Speed vs. Time Which graph segments
; fit the following:
A Constant speed: A+C
Deceleration: B
Speed
Accelerating: D
Speed (m/s)
0 2 4°6 8 1 12 | lime
The slope of a Speed vs. time graph means:
Velo: Жи»
Find the acceleration for the above graph:
pU-O be | The siope of à Speed vs. time graph means: