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The Car & Ramp CPO Science

The Car & Ramp CPO Science. Key Questions How do we measure and describe the world around us? What is speed and how do we measure it? Can you predict

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The Car & RampCPO Science

Key Questions 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?

Overview Timer Functions

Using the Timer

Measuring Speed

Graphing Speed

Predicting Speed from our Graph

CPO Timing System

CPO Timing System How can we measure time accurately?

Using the timer in stopwatch mode; Who can get the fastest time?

The 100 meter race One runner has a time of 10.01 seconds Another runner has a time of 10.00 seconds Who wins?

Photogates How does the Photogate start and stop

the timer? Do the speed challenge.

What happens when you block the light beam several times in succession; does the timer reset, or does it add the times?

Plug the second photogate into the B port.

How does the timer work like 3 internal stopwatches?

Review How do you start the timer?

How do you stop the timer?

If you block the light beam several times in a row, does the timer start from zero each time, or are the times added?

What does the timer measure when the A light is on?

What does the timer measure when the B light is on?

What does the timer measure when both lights are on?

Motion Investigation #1

Why does the car have a tab on the side?

Foot

R am p

PhysicsS tand

C ar

Light Beam

Photogate C lam p

C ar

Design a quick experiment to see what effect ramp height has on the TIME it takes the car to move from Photogate A to Photogate B. Ramp hole #: 3, 5, 7, 9

Ramp Height

What Happened? What are the variables in this

experiment?1. Distance between A & B2. position of A & B3. Weight4. starting point5. friction6. start technique7. Ramp angle

Technique

Practice your drop technique until you get three identical times in a row! This is very important for data collection in the next investigation!

Now Let’s try that experiment again, and this time we will do our best to control all variables except ramp height.

Controlling Variables

The One-Foot Race

How Fast? Match them up!(m/s)

1. Human fast walk

2. Snail

3. Hair growth

4. Continental drift

5. Concorde SST

6. Winner of 100 m dash

7. Tsunami (tidal wave)

8. Running cheetah

9. Fastball pitch (Nolan Ryan, 1974)

A. 1.2 x 101

B. 4.5 x 101

C. 7.1 x 102

D. 2.8 x 101

E. 2.0 x 102

F. 3.0 x 10-9

G. 1.0 x 10-3

H. 1.3 x 100

I. 1.0 x 10-9

How Fast? Match them up! (m/s)

1. Human fast walk

2. Snail

3. Hair growth

4. Continental drift

5. Concorde SST

6. Winner of 100 m dash

7. Tsunami (tidal wave)

8. Running cheetah

9. Fastball pitch (Nolan Ryan, 1974)

H. 1.3 x 100

G. 1.0 x 10-3

F. 3.0 x 10-9

I. 1.0 x 10-9

C. 7.1 x 102

A. 1.2 x 101

E. 2.0 x 102

D. 2.8 x 101

B. 4.5 x 101

Using a model to predict speed of car

Turn to investigation 2.1, Foundations of Physical Science Investigation Manual

Make a Graph of Speed vs. Displacement

Why do we start with this graph?

Only need 1 photogate Can make predictions with graph

What is the dependent variable, and do we assign it to the X or Y?

What is the independent variable?

Should we connect the data points?

What does the graph tell us about the speed of the car as it rolls down the ramp?

Explain why the graph is a curve

Test the Graphical Model Connect the data points on your graph

Without using the car/ramp setup, predict what the speed of the car at clamp B would be if the photogates were 27 cm apart.

Test your prediction!

Calculate % error

The amazing Carnak Place the Photogate at the 38 cm mark

Turn the timer face down on the table

Run the car down the ramp; DON’T TURN THE TIMER OVER, THAT’S CHEATING

Use your graph and a little algebra to predict the time on the display

Write the time on your white board

Turn the timer over! How close were you?

Calculate % error

THIS IS YOUR GRADE!

Position vs. Time

Suppose we want to collect data and graph the relationship between displacement of the car and time (distance vs. time graph). How do we measure the distance? How do we measure the time? What change in our setup is required?

Place photogate A at the top of the ramp, but be sure the wing doesn’t break the beam while the car is at rest. Don’t move A!!!

Place Photogate B at 6 different places along the ramp.

Measure: Displacement (distance from A to B) Time A, Time B, Time from A to B

Series of Trials

What is the dependent variable?

Displacement; the distance the car moves depends on how much time has elapsed

What is the independent variable?

The time it took the car to move from A to B

Create the d/t graph.

What does the graph tell us about the motion of the car?

Why is the graph a curve?

Graphing Data

Time to make another prediction! Place the photogates 55 cm apart. Turn the timer over and run the car

down the ramp

What will the timer read? Make your prediction, check it, and calculate % error

What is your grade on this investigation?

Using a Graph for Predictions

What is acceleration?

How could we find the acceleration of the car on the ramp?

Place photogates 20 cm apart at different places on the ramp, and find acceleration

How do accelerations compare at different places on the ramp?

How could I make the acceleration greater?

Acceleration

What other combination of variables have we not yet graphed and investigated? Speed of car vs. elapsed time

Do we need to run more trials to collect data for this? No, we need to calculate speed at B

from previous data

Calculate speed at B for each of the trials in investigation #3

Testing Different Variables

What is the dependent variable? Speed at B; it depends on the time elapsed

What is the independent variable? Time elapsed from A to B

Create a graph of Speed vs. Time

More Graphing

What is different about the “look” of this graph when compared to the

other two graphs we created?

It’s a line! What equation describes the relationship between x and y variables for a straight line?

y=mx+b

Substitute variable names from our experiment for each of the letters in the equation y=mx+b.

What does y represent? Speed at b, or VB

What does x represent? Time elapsed, or tAB

What does b represent? This is a challenge! Check out the other data we

collected and see if you can figure it out Speed at A, or VA

Using the Line Equation

What does m represent? Slope of the line How do you find the slope? Change in y over change in x What quantity is defined as the

change in speed over time? Acceleration!

Write the equation of the line using the physics variables VB = at + VA

Physical Science teachers will recognize this as a= (Vf – Vo)/t

You have just used a graph to show the relationship between 4 different physical variables! You derived the equation for finding acceleration!

Use your graph to find b (VA) & m (a)

Rearanging the Equation

For each of the following times, use your equation to find the speed at B and plot these data points on your experimental graph of speed vs. time T= 0.2000, 0.3000, 0.4000, 0.5000 Find VB for each of these times Plot the ordered pairs on your

experimental graph

How close does your prediction match your experiment?

Prediction Vs. Experiment

In many situations, like the car/ramp, the distance, speed, time, and acceleration are all important variables.

We know how to relate speed, distance, and time s = d/t; but without acceleration.

We know how to relate speed, time, and acceleration a = (Vf – Vo)/t; but without distance.

How do we relate all four variables for a more general description of motion?

Summary

See handout with explanation of finding area under speed/time graph