Negative acceleration

2. What is the relationship between initial
velocity and braking distance?
In today’s lab, we will be looking at the
relationship between initial velocity and
braking distance.
On the next clean lab page in your lab
notebook, write “Section 5 – Negative
Acceleration”
Don’t forget to make an entry in your Table
of Contents

3. What is the relationship between initial
velocity and braking distance?
Before we do the lab, form a hypothesis with
your group about the relationship between
initial velocity and braking distance.
Remember:
A good hypothesis always contains an “if”
and a “then”

4. What is the relationship between initial
velocity and braking distance?
With your lab group, answer all eight
questions in the right-hand column on pg
76 in your lab books.
After you have answered all eight questions,
create a numbered procedure for how your
group will conduct the investigation.
You must get approval before conducting
your investigation.

5. What is the relationship between initial
velocity and braking distance?
For your plan to be approved, your group will
need to have an answer for all eight
questions on pg 76 as well as at least one
well-constructed data table with which to
collect your data.

6. What is the relationship between initial
velocity and braking distance?
For the first 10 minutes of class, we will be
working on interpreting our lab results (on
page 77, #5a, 5b)
You may work in your lab group, but you
must be working or you will be separated.

7. Negative Acceleration
Review: What is acceleration?
acceleration is a change in velocity
Review: What are three ways velocity can
change?
speed up
slow down
change direction

8. What’s Negative, What’s Positive?
While we discuss the ways an object has
negative acceleration, it is important to
remember that movement is either in a
positive direction or a negative direction
if east is positive, then moving west is
negative
if moving up is positive, them moving
down is…
negative

9. What’s Negative, What’s Positive?
It will also be helpful to keep in mind that if
an object is decreasing its speed, it will
have “negative” speed (V
f
– V
i
)

10. Negative Acceleration
An object can have a negative
acceleration when it:
1. decreases its speed when moving
in the positive direction

11. Negative Acceleration
An object can have a negative acceleration
when it:
2. increases its speed when moving in the
negative direction

12. Positive Acceleration
An object can have a positive acceleration
when it:
1. increases its speed in the positive
direction
2. decreases its speed when moving in the
negative direction

13. Calculating Braking Distance
We can use the formula below to calculate
braking distance
where
d = braking distance
V
f
2
=2ad+V
i
2

14. Calculating Braking Distance
If we are talking about braking to a stop, then
V
f
= 0
So we can re-write the equation to look like
this:
V
f
2
=2ad+V
i
2
-2ad=V
i
2