October 2014
Firstly

Homework check
Changes in Velocity
Imagine:
You’re in an airplane going to __________.
During take-off, you feel the airplane moving
and your body is pushed back in the seat.
Once you’re in the air, you don’t feel
anything. What is happening with these
changes in motion?

Changes in Velocity

We call theses changes in velocity
“acceleration”

How is acceleration (change in velocity)
different than constant velocity?
Changes in Velocity
Changes in Velocity
On a position-time graph, acceleration is
always curved
 On a velocity-time graph, when
acceleration increases or decreases
uniformly, it is a straight line
 When an objects speed does not increase
or decrease, it is uniform motion, so how
does that look on a velocity-time graph?

Changes in Velocity

This is uniform
motion/constant velocity
on a velocity-time graph

This is uniform motion on
a position-time graph
Changes in Velocity

When an object’s velocity is decreasing,
slowing down or moving in a negative
direction, we call that negative acceleration

You can use deceleration, but it is technically
not a scientific term, because it only refers
to the objects speed, not direction
Changes in Velocity

Now, we have 3 graph types
 Distance vs. Time  Speed
 Position vs. Time  Velocity
 Velocity vs. Time  Acceleration
 We use them to calculate different things for
different reasons, when would we use them
differently and why?
Changes in Velocity

Let’s draw different speeds and velocities on
different types of graphs...
 Distance-Time Graph
○ Constant speed *
○ Changing speed *
 Position-Time Graph
○ Positive uniform motion *
○ Negative uniform motion *
○ No motion *
○ Positive acceleration *
○ Negative acceleration *
 Velocity-Time Graph
○ Positive acceleration
○ Negative acceleration
Changes in Velocity
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
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
Lab #3 – The Moving Man Lab
*Requires your laptop*
We are not calculating acceleration, but
ensuring that we understand how they look
different on different graphs
This is an individual activity, unless you forgot
to bring a computer or the program doesn’t
work for you
We will finish this in class on Wednesday
Some changes…
I’m unable to have the science final exam
worth 25%, so I’m dropping it to 20%
 I put this 5% into your presentation mark,
so now the presentation is worth 10%


Due to lack of frequent homework in this
class, I’ve combined in class work and
homework together to be work 20%,
rather than 10% (this is better for you!)
6.1 – Accelerated Motion

We can use velocity-time graphs to
calculate acceleration, but we can also use
them to calculate displacement

Before we jump into this, what is the unit
of measurement for acceleration?
 Velocity + Time
○ Example - (m/s²)
Page 242 Sample Problem

Step 1
 Understand the question! Look for key words

Step 2
 Identify all numbers given

Step 3
 Strategize
○ Do you remember the word ‘composite’?
Page 242 Sample Problem

Step 1
 Understand the question! Look for key words
○ “…a velocity of 14 m/s[S]…”
○ “0.50s to react… to stop the car.”
○ “…time that the car stopped is 3.0s.”
○ “…determine the displacement…during that 3.0s”
Page 242 Sample Problem

Step 2
 Identify all numbers given
○ “…a velocity of 14 m/s[S] …”
○ “0.50s to react… to stop the car.”
○ “…time that the car stopped is 3.0s.”
○ “…determine the displacement…during that 3.0s”
Page 242 Sample Problem

Step 3
 Strategize
○ Do you remember the word ‘composite’?
○ Draw the graph!
Page 242 Sample Problem

Step 3
 Strategize
○ What are we doing when we calculate the area?
○ Why does the area under a velocity-time graph
equal the displacement of the object?
○ https://www.khanacademy.org/science/physics/
one-dimensionalmotion/acceleration_tutorial/v/why-distance-isarea-under-velocity-time-line
Sample Problem

Let’s try 243 #1 together
Sample Problem

You try #2 and #3 now
Types of acceleration

Zero acceleration
 Only 2 neutralized forces acting on you

Positive acceleration
 An additional force pushes you forward

Negative acceleration
 An additional force pushes you back
Section Review
All questions, due next week
 I would like to work on
some of these questions
with a few students in class
