Key Questions2.1 : Modeling car’s speed

How do we measure and describe the world around us?

What is speed and how do we measure it?

Can you predict the speed of the car at any given point on the ramp?

Review

Set up and explain how you would use the photogates and timer to find the average speed of the car on the ramp

Set up and explain how you would use one photogate on the ramp to find an instantaneous speed of the car at some point on the ramp

Review

What does the timer display for you when the A light is on?– B light?– Both A and B lights?– No lights?

Does the timer reset itself?

Do you have to run the car down the ramp multiple times to get the time at A, time at B, and the time from A to B?

Investigation 2.1What Are Models?

Scientific Model

Physical Model

Conceptual Model

Graphical or Mathmatical Model

Developing Models

Does the car travel the same speed the entire way down the ramp?

How much faster is it going at the bottom? Twice or three times as fast?

Can we develop an experiment to answer this question?

What materials will we need?

What are the variables?– Which is the independent, and which is the

dependent?

What do we do with the variables we are not testing?

Developing An Experiment

Developing An Experiment

What data will we record?– Time through the

photogate– Position of photogate

What will we need to calculate?– Speed of car, d/t (tricky!

What is the value for d?)

Run The ExperimentSet up the car & ramp

and record the data

Tips:• Be careful at the top

and the bottom of the ramp

• 10 cm is a good interval between data points

Graph your DataLook for trends in your data

before graphing

What variable should be placed on the X axis?

What variable should be placed on the Y?

What does the graph show?

How can we use this graphical model to predict the speed of the car at a position we did not include in our data?

Use your graphical model to predict the speed of the car at 47.0 cm

Calculate percent error

See part 4, investigation 2.1

YOUR GRADE =(100 – percent error)

Summary

Is there a cause and effect relationship between the speed of the car and its location on the ramp?

• How do you know?

Is the relationship strong or weak?

Is the relationship linear?

Is it a direct or inverse relationship ?

Key Questions2.2: position vs. time

What is the relationship between speed, distance, and time of the car on the ramp?

How can we determine speed from a distance vs. time graph?

What materials will we need?

What are the variables?– Displacement of the car (distance between

variables)– Time it takes for that displacement to occur

We will collect all the data that is available, so we can use it in the next investigation!

Developing An Experiment

Developing An Experiment

What data will we record?– Distance from A to B– Time from A to B– Time at A– Time at B

What will we need to calculate?– Speed of car at A– Speed of car at B

Run The ExperimentSet up the car & ramp

and record the data

Tips:• Be careful at the top

and the bottom of the ramp

• 10 cm is a good interval between photogates

Graph your DataLook for trends in your data

before graphingWhat variable should be

placed on the X axis?– TIME A to B

What variable should be placed on the Y?– DISTANCE A to B

What does the graph show?How can we use this graph to

find the speed of the car at different places on the ramp?

Use your graphical model to find the speed of the car at two different places; find the slope

between two sets of points on the graph

Key Questions2.3: acceleration

Is the speed of the car changing as it moves down the ramp?

What is acceleration?

What is the difference between acceleration and speed?

A quick way to find the value for acceleration on the ramp

Place your ramp in hole #5 from the bottom

Use two photogates, and figure out what you need to do to find the value for acceleration on this ramp.

How will acceleration be calculated? What data do you therefore need to collect?

Run A Pre-ExperimentWhen you find your value for acceleration, what will

the unit be?– cm/s/s or cm/s2

Finding acceleration another way

Okay, now how could we use a graph to find the acceleration of the car on the ramp?

Construct a speed/time graph and find the slope!

Key Questions3.1: Newton’s 2nd law

What is a force?

How does varying the force on the car, while keeping its mass constant, affect its acceleration?

What is the relationship between force, mass, and acceleration?

Modification for 3.1

Rather than collecting more data, simply think this experiment through with the entire class

After discussing (use a car/ramp setup to demo as you lead the discussion), give data from teacher’s guide to groups and have them try graphing different combinations of the force, mass, acceleration data

Data for 3.1

Relationship between force, mass, and acceleration

Key Questions3.2: Weight, Gravity, Friction

• How is motion affected by friction?

• Do heavier objects fall faster than lighter objects?

• What is friction?

Developing An Experiment

What happened?

Does changing the mass significantly affect the speed of the car?

Why or why not?

Key Questions3.3: Newton’s 3rd law

What do we mean by action and reaction?

Why don’t equal and opposite forces cancel each other out?

What does Newton’s third law mean to everyday experiences?

What is equilibrium, and how does it relate to forces?

Concept development

1. Use the car and ramp to set up an action/reaction situation. Diagram, label forces, and discuss.

2. Use the car and ramp to set up an equilbrium situation (level ramp). Take data on speed of the car and discuss.

3. Use Newton’s 3rd law to discuss everyday scenarios and examples of action/reaction