Monday: Pg. 18 or 24(if no room on 18)
Match the unit
1.
2.
3.
4.
5.
Speed
Velocity
Distance
Displacment
time
a)
b)
c)
d)
e)
Pick up the handout
Titled, “Physics” when
You pick up journal.
4 Hrs
3 Km west
m/s
- 4 cm/min
12 meters
Instructions: Write everything
then match.
Thursday (pg. 18)
• Can an object accelerate but have a
negative value (magnitude)? Ex. -3.4 m/s2
Instructions: Answer in a
complete sentence/provide
an example.
Lab analysis
1. How did the speed change over time for
each runner?
2. How did the acceleration of each runner
compare to each other?
3. Predict what a speed vs time graph would
look like with your data.
When you begin to graph distance
vs time, you will have to renumber
your axes.
Wednesday: Pg. 24(if no room on 18)
Pick up the pumpkin carving contest
paper on the table.
a) If distance wasn’t measured in the track
activity, how could you use acceleration, time
and velocity to determine it?
Instructions: Write answer in complete sentence or
you can use an equation to show how you would
solve for it (it is ok to make up numbers for the
variables).
Graph Analysis
4. Was the prediction you made in #3
correct?
5. Compare the lines for the two runners on
your distance vs time graph.
6. Compare the lines for the two runners on
your velocity vs time graph.
7. Choose one runner, does his line on the
distance vs time graph look the same as
his line on the velocity vs time graph?
Why or why not?
Chp. 2 Section 2
Acceleration
RECAP!
• Speed is the magnitude of velocity
• Velocity must include direction which can
be positive or negative
• Speed is a scalar quantity and velocity is a
vector quantity
• Speed has distance and velocity has
displacement
• A graph can be used to determine if
speed/velocity is constant or changing
Why are roller coasters so much
fun to ride?
• It is a combination of fast
velocities and changes in
velocity, or acceleration.
The average acceleration of an object is defined
to be the ratio of its change in velocity to the
time taken to change the velocity.
v
aav =
t
aav = average acceleration;
in units of m/s2 ; length/time2
v = change in velocity;
in units of m/s; length/ time
t = change in time;
in units of s; time
Velocity and
Acceleration
• Copy table. We will
use it to answer the
questions that follows.
• If a baseball has zero velocity at some
instant, is the acceleration of the baseball
necessarily zero at that instant?
• If a passenger train is traveling on a
straight track with a negative velocity and
a positive acceleration, is it speeding up or
slowing down?
• When Jennifer is out for a ride, she slows
down on her bike as she approaches a
group of hikers on a trail. Explain how her
acceleration can be positive even though
her speed is decreasing.
Important basic facts when
working with acceleration:
• If an objects starts from rest,
its initial velocity is 0.
• If an object stops, its final
velocity is 0.
• If an objects falls in the air,
it is accelerated by gravity
at -9.8 m/s2.
The slope and shape of the graph
describe the object’s motion
Draw Graph in Journal
You can learn more about distance,
displacement, speed, velocity,
relative velocity, and acceleration
by clicking on these simulation links:
link1, link2, link3, link4, link5
KINEMATIC
Motion with constant acceleration
• When velocity
increases by exactly
the same amount
during each time
interval, acceleration
is constant;
• Constant distance
equal constant
velocity equal
constant
accelereation
There are many formulas
associated with acceleration
vf = vi + at
No x
x = ½ (vf + vi)t
No a
x = vit +
2
½at
Vf2 = vi2 + 2ax
No vf
No t
Choose the Correct Equation!!!!!!!
2. A plane starting at rest at one end of a runway undergoes a
uniform acceleration of 4.8m/s2 for 15s before takeoff. What is
its speed at takeoff? How long must the runway be for the
plane to be able to take off?
A plane starting at rest at one end of a runway undergoes a
uniform acceleration of 4.8m/s2 for 15s before takeoff. What
is its speed at takeoff? How long must the runway be for the
plane to be able to take off?
Part A:
Given: vi= 0 m/s; t= 15s; a = 4.8m/s2
Formula: vf = vi + a∆t
Substitution: vf= 0 + (4.8m/s2)(15s)
Answer w/unit: 72.0m/s
Part B:
Formula: ∆x = vi∆t + ½ a(∆t)2
Substitution: ∆x = 0(15) + ½ (4.8) (152)
Answer w/unit: 540. m
Answer to #2.
Which equation would I use?
Use this equation when you want to find the final velocity of a uniformly accelerated
object without knowing how long it has been accelerating.
A person pushing a stroller starts from rest uniformly
accelerating at a rate 0.500m/s1. What is the velocity
of the stroller after it has traveled 4.75m?
Given: a=0.500m/s2; vi = 0m/s; x= 4.75m
Formula: vf2= vi2 + 2a∆x
Substitution vf2= 0 + 2(0.500m/s2)(4.75m)
Answer w/unit: √4.75 =2.18m/s
1. An aircraft has a landing speed of 83.9m/s. The landing area
of an aircraft carrier is 195m long. What is the minimum uniform
acceleration required for a safe landing?
Given: vi = 83.9m/s; x= 195m; vf=0
Formula: a= vf2-vi2
Substitution: a= -83.92
2(195)
2∆x
Answer w/unit: -18.0m/s2
2. An electron is accelerated uniformly from rest in an accelerator
at 4.5 x 107 m/s2 over a distance of 95km. Assuming constant
acceleration, what is the final velocity of the electron?
Given: vi = 0m/s; x= 95000m; a=4.5 x 107 m/s2
Formula: vf2= vi2 + 2a∆x
Substitution vf2= 0 + 2(4.5 x 107m/s2)(95000m)
Answer w/unit: 2.92 x 106 m/s
A cyclist traveling at 5.0 m/s accelerates with an
average acceleration of 1.5 m/s2 for 5.2 s. How
large is her final velocity?
A train traveling at 6.4 m/s accelerates at 0.10
m/s2 over a distance of 100 m. How large is the
train’s final velocity?
A ball rolls past a mark on an incline at 0.40 m/s. If
the ball has an average acceleration of 0.20
m/s2, what is its velocity 3.0 s after it passes the
mark?
A car initially traveling at 15 m/s accelerates
at a constant rate of 4.5 m/s2 over a
distance of 45 m. How long does it take
the car to cover this distance?
A car accelerates from 10.0 m/s to 15.0 m/s
in 3.0 s. How far does the car travel?
A race car accelerates at 4.5 m/s2 from rest.
What is the car’s velocity after it has
traveled 35.0 m?
vf = vi + at
t = time
∆x = ½ (vi+vf)∆t
vi = initial velocity
∆x = vit + ½
2
a(∆t)
vf2 = vi2 + 2a∆x
∆x= displacement
a = acceleration
vf = final velocity