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

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”

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.

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.

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.

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

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

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 (Vf – Vi)

Negative Acceleration

An object can have a negative acceleration when it:

1. decreases its speed when moving in the positive direction

Negative Acceleration

An object can have a negative acceleration when it:

2. increases its speed when moving in the negative direction

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

Calculating Braking Distance

We can use the formula below to calculate braking distance

where

d = braking distance

Vf 2 = 2ad + Vi

2

Calculating Braking Distance

If we are talking about braking to a stop, then Vf = 0

So we can re-write the equation to look like this:

Vf 2 = 2ad + Vi

2

-2ad = Vi2