1. Acceleration

2. Now, that’s acceleration!

3. rate of change in velocity
acceleration, a = ____________________________
a vector (has mag. and dir.)
=______________________________
average a = where Δv =
Any time that _____________ changes, there
is___________________. And because:
velocity =
speed
direction,
changing either _____________ or ______________
or _________ results in acceleration. In this
section, we only consider changes in __________ .
The _________ speed changes, the _________ the a.

4. PhysRT, last page:

5. rate of change in velocity
acceleration, a = ____________________________
a vector (has mag. and dir.)
=______________________________
average a = where Δv =
Δv/t
vf - vi
Any time that _____________ changes, there
is___________________. And because:
velocity =
velocity
acceleration
speed
direction,
changing either _____________ or ______________
or _________ results in acceleration. In this
section, we only consider changes in __________ .
The _________ speed changes, the _________ the a.
speed
direction
both
speed
faster
more

6. Ex: Mr. Siudy accelerates his jet skis from a
speed of 5.0 m/s to a speed of 17 m/s in 3.0 s.
Find the magnitude of her acceleration.
a = Δv/t
vi = 5.0 m/s
= (vf – vi)/t
vf = 17 m/s
= (17 m/s – 5.0 m/s)
3.0 s
t = 3.0 s
a = ?
= 12 m/s
3.0 s
= 4 m/s s
= 4 m/s2

7. SI units for a:
m/s = s
m/s2
 derived
other units:
mph , s
cm , s2
km/h s
Using brackets [ ] for units:
[a] =
[speed]
[time]
= [distance]/[time]
[time]
= [distance]
[time]2
4 m/s of
speed
_________
gained
each
From last problem:
a =
4 m/s2
= 4 m/s s
second

8. Because a = _________ , the ________________
of a is the same as the __________________
of the ________________in v: Dv = vf - vi.
direction
Dv/t
direction
change
Ex 1: An object moving to the right
accelerates to a faster speed. vi vf
Dv =
vf – vi vf
= vf + (-vi) Dv
-vi
to the right
Since Dv ____ 0 (which is _________________),
then also the acceleration a ____ 0.
>
>

9. Ex 2: An object moving to the right is
slowing down, or ________________________.
decelerating vi vf
Dv =
vf – vi Dv vf
= vf + (-vi)
-vi
Since Dv ____ 0, then also a ____ 0.
Note that the direction of the acceleration
______________ always the same as the
direction of the ___________________ .
<
<
is NOT
velocity

11. Ex 3: An object moving up
but slowing down: vf vf
Dv =
vf – vi
-vi
= vf + (-vi) Dv vi
 a is ______________ or_______________.
negative
downward
Conclusions:
If the ___________ and the________________
are in the __________ direction, then the object is
_________________ ( __________________) .
2. If the ___________ and the________________
are in _______________ directions, then the object
is _________________ ( __________________) .
velocity
acceleration
same
accelerating
speeding up
velocity
acceleration
opposite
decelerating
slowing down

12. _______________can be confusing, but remember:
The __________________ is always from the
_________________ to the _____________ points.
The ________________ always has the same
direction as the object's ____________________
(the _________ direction it __________________).
The ___________________ has a direction given
by the direction of the ____________ in the
______________ , which may or may not be the
same as the direction of the ________________ .
Directions
displacement
initial
final
initial
final
velocity
displacement
same
is moving
acceleration
change
velocity, Dv
velocity

13. Ex: The _________________of the acceleration is
also called the__________________________.
magnitude
acceleration
a = 2.0 m/s2, east =
+ 2.0 m/s2
mag.
dir.
In review:
scalar
…is the
magnitude
of the…
vector
distance
displacement
speed
velocity
acceleration

14. _ In word problems, remember: 1) “starts from rest” means  vi =0
2) “comes to rest” means 
vf =0
When an object is in ______________motion,
it means it has a _________________velocity. In
that case: __________ and ____ = _____ = _____
uniform
constant
a = 0 v vf vi
light and sound
Examples: The speed of _____________________
given in the PhysRT are ___________________.
constants
up/right are___________________,
down/left are____________________. + _

15. Ex: A ball is dropped. It accelerates from rest
to a speed of 29 m/s in 3.0 seconds. Finds its
acceleration.
“from rest”  vi = 0
a = Δv/t
vf = -29 m/s (down)
a = (vf – vi)/t
t = 3.0 s
a = -29 m/s -0
3.0 s
a = ?
a = m/s2
What are the magnitude and direction of a?
How much speed does the ball gain each
second?
9.7 m/s2
down (neg.)
9.7 m/s

16. Starting from:
a = Δv/t
a = (vf – vi)/t
at = vf – vi
vf = vi + at
PhysRT, last page:

17. Ex: What is the speed of a giraffe, initially moving
at a speed of 21 m/s, that accelerates at 5.0 m/s2
for 2.0 s?
vf = vi + at
vi = 21 m/s
= 21 m/s m/s2(2.0 s)
a= 5.0 m/s2
= 21 m/s m/s
t = 2.0 s
= 31 m/s
vf = ?
If it remains at this final speed, how long will it
take to travel 100. m? v
= d/t
vf = v = 31 m/s
31 = 100 / t
d = 100. m
t = 3.2 s

18. Ex: Chuck Norris accelerates from a speed of
4.0 m/s to 10. m/s in 4.0 seconds. Find his
average speed during that time. v
= (vi + vf) 2
not in PhyRT
= (4.0 m/s m/s) 2
= 7.0 m/s
How far does he travel in the 4.0 s? v
= d/t
d = v t
= (7.0 m/s)(4.0 s)
= 28 m
Why can't you use vi or vf to find d?