Transcript notes

September 30, 2005
Homework:
 Review ALL labs and notes nightly. FINAL EXAM IN FIVE
PERIODS.
Complete practice problems if you do not complete the work in
class. You should do them again later as test review!

Velocity
What is the formula for calculating speed?
s = d/t
If a hurricane travels 38 km in two hours, her speed is _____.
s = 38 km/ 2 h
s = 19 km/h
Velocity is speed with direction.
“Rita IS MOVING TOWARD THE WEST 19 KM/HR”
19 km/h doesn’t give enough information so direction is needed.
Acceleration mathematically is the rate of speed CHANGE.
Velocity (speed) is measured in distance per unit of time.
Acceleration is change in a unit of time.
So….
Velocity (d/t) divided by change per time (t) =
Acceleration d/t/t or d/t2
Usually acceleration is measured in m/sec2 but can be
something else like km/hour/sec.
Solving for and Graphing Acceleration
If you are given only velocity information in a problem and are
asked to solve for acceleration, you will need to use the following
formula.
Acceleration = final velocity – beginning velocity
time
An eagle accelerates from 15 m/sec to 22 m/sec in 4
seconds. What is the eagle's average acceleration?
Try to solve.
Acceleration = final velocity – beginning velocity
time
An eagle accelerates from 15 m/sec to 22 m/sec in 4
seconds. What is the eagle's average acceleration?
Acceleration = final velocity – beginning velocity
time
a = 22 m/sec – 15 m/sec
4 sec
a = 7 m/sec / 4 sec
a = 1.75 m/sec/sec
(1.75 m/sec2)
Solving for and Graphing Acceleration
We now know that for each second of travel, the eagle went faster
by an additional 1.75 m/sec for a total acceleration of 1.75 m/sec2
Set up a data table with two columns: time and speed
Time (seconds)
Speed (m/sec)
Solving for and Graphing Acceleration
An eagle accelerates from 15 m/sec to 22 m/sec in 4
seconds which is an acceleration rate of 1.75 m/sec2.
Time (seconds)
0
Speed (m/sec)
15 m/sec
Solving for and Graphing Acceleration
An eagle accelerates from 15 m/sec to 22 m/sec in 4
seconds which is an acceleration rate of 1.75 m/sec2.
Time (seconds)
0
1
2
Speed (m/sec)
15 m/sec
Solving for and Graphing Acceleration
An eagle accelerates from 15 m/sec to 22 m/sec in 4
seconds which is an acceleration rate of 1.75 m/sec2.
Time (seconds)
0
1
2
3
4
Speed (m/sec)
15 m/sec
16.75 m/sec
18.5 m/sec
20.25 m/sec
22 m/sec
Solving for and Graphing Acceleration
An eagle accelerates from 15 m/sec to 22 m/sec in 4 seconds which is an
acceleration rate of 1.75 m/sec2.
Time (seconds)
Speed (m/sec)
0
15 m/sec
1
16.75 m/sec
2
18.5 m/sec
3
20.25 m/sec
4
22 m/sec
Set up a graph to show the rate of acceleration. The x-axis is ‘time’ and
the y-axis is ‘speed.’ By sure to title your graph as well!
Plot all the data in the data table on a line graph. What type of
acceleration does this show?
Eagle's Acceleration
25
20
22
20.25
Speed (m/sec)
18.5
16.75
15
15
10
5
0
0
0.5
1
1.5
2
2.5
Time (sec)
3
3.5
4
4.5
Newton’s Second Law – UPDATE your notebook
Objects accelerate…

in direct proportion to the applied force,

in inverse proportion to their mass.
Mathematically, this is: a = F/m
a = acceleration = m/s2 (meters per second squared)
F = force = N (Newton’s)
m = mass = kg (kilograms)
1. If a 2 kg bird is pushed by
the wind with a force of 2 N,
how fast does the bird
accelerate?
a = F/ m
a = 2 N / 2 kg
a = 2/2 or a = 1 m/s/s
2. How much force is
needed to accelerate a 25
kg bowling ball at 2 m/s2?
a = F/ m
2 m/s2 = F / 25 kg
25 kg x 2 m/s2 = F / 25 kg x 25 kg
25 x 2 = (F / 25) x 25
50 = F
F is 50 N
3. How much force is
needed to accelerate a 3 kg
skateboard at 5 m/s2?
a = F/ m
5 m/s2 = F / 3 kg
3 kg x 5 m/s2 = (F / 3 kg) x 3 kg
3 x 5 = (F / 3) x 3
15 = F
F is 15 N
a = 1 m/s2
Exam Practice – Use a textbook. Copy the assignment below.
You must have finished through labs 24 to begin working on
this. When you begin this exam practice, copy each question
into your notebook. Show work.
Page 40 M
• #s 2 – 5, 7, 9 – 10, 12 – 14, 18 – 20, 22 – 23
Page 53 M
• Practice Problems 1 – 2 at the bottom of the page.
Page 54 M
• Section 2 Review questions 1-4.
Page 58 M – 59 M: Read “Gravity-Free Fall” and “Air Resistance.”
Answer question number 4 on page 61 M.
Page 74 M
• #s 1-4, 11-12, 15, 25-27