Finding acceleration with Photogates - Columbia Public Schools

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Finding acceleration with Photogates

Name ______________________________ Block ______

Lesson Objective: To understand how to collect data using photogates.

means check with your teacher before moving on.

Materials: CPO Timer, 8.5x10 piece of paper (this one works great!)

How do the timers/photogates work? 1. Using the timer as a stopwatch: The electronic timer allows us to make accurate, precise measurements of time. The timer performs many different functions. The first function to try is stopwatch. Use the mode button (1) to move the light under the word stopwatch.

A stopwatch measures a time interval. The stopwatch is started and stopped with the "A" button (2). The display shows time in seconds up to 60 seconds, then changes to show minutes: seconds for times longer than one minute.

Try this out: The time it takes a signal to go from your brain to move a muscle is called reaction time. Reaction time varies from person to person and can be affected by factors like tiredness or caffeine intake. Design a method to measure the reaction time of a person by turning the stopwatch on/off as quickly as possible. Touch the A button gently.

1. Set timer to stopwatch 2. Start and stop the stopwatch with the `A"

button 3. Reset the stopwatch to zero with the "0"

button

a. Use the method you designed to take measurements with the stopwatch for each person in your group. Your data table:

b. Find the average reaction time for your group. (show work)

2. Using the photogates A photogate allows us to use a light beam to start and stop the timer. When the timer is in interval mode, it uses photogates to control the clock. 1. Connect a single photogate to the "A" input with the red cord. 2. Select interval on the timer. 3. Push the "A" button and the "A" light should come on and stay on. 4. Try blocking the light beam with your finger and observe what happens to the timer. Because it is used for so many measurements, you need to figure out how the photogate and timer work together.

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Try your own experiments until you can answer the questions. a. Exactly what do you do to start and stop the clock using just the photogate? Be very specific in your answer.

Start: Stop: b. Explain what the timer is measuring when you run the 11 inch side of a paper slowly through the beam long ways once.

c. Does the time add up on the clock or does the timer restart at zero every time you break the beam without hitting the reset button? Provide numbers to back up your statements.

d. Move a piece of paper through the photogate on the 8.5 inch side. The timer started timing when _____________________________________________________________

The timer stopped timing when _____________________________________________________________

The front edge of the paper moved ________ inches while the timer timed. Time on the timer was__________. e. So what is the photogate measuring?

How can you use the information about the paper in part d. to calculate its velocity from the velocity

equation?

3. Two photogates

The timer can be used with two photogates. Photogate A is connected to the A input and photogate B is

connected to the B input with the blue cord. What the timer shows depends on the lights above the buttons.

Pushing the A or B buttons toggles the A or B light on or off. Do your own experiments until you can fill in

Table 1.

A light B light How do you start the How do you stop the This is the time it took for me

clock?

clock?

to...

On

Off

Off

On

On

On

Off

Off

4. Reset Timer. Run a pencil through Photogate A and then through B once. Now turn on A light only. Turn

on B light only. Turn on A & B lights. Record each time below.

A time: _______________ B time: _________________

A& B time: _______________

The AB time is the time it took for the pencil to _____________________.

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How objects fall



Name ___________________

PRE-LAB What do you think? 1) How do objects move when they fall short distances?

(at a constant speed, speed up, slow down speed up & then go at a constant speed)

2) Do heavy objects fall at the same rate as light objects? (Yes or No) What do you predict? (light objects fall faster, heavy objects fall faster, all objects fall at the same rate)

Materials: CPO Gravity Drop, CPO Timer, Marble

Procedure:

1 Set up the Gravity Drop apparatus.

2 Make sure that the marble falls cleanly into the base. Adjust the knobs on the bottom of

the stand until it does. Once it works- DON'T MOVE the stand!

3 Place photogate A directly over the hole in the stand just below the marble holder,

which is 5 cm below. (FYI: Holes in the stand are 5 cm apart)

4 Place photogate B 40 cm below photogate A directly over the hole in the stand.

5 Place the marble in the top clamp and practice dropping it into the base before actual

testing. Make sure that the clamp just barely holds the marble & that you slowly release

the marble from its holder clamp.

6 Turn the timer onto interval and release the marble.

7 Record all three times (s) on the diagram below for your trial. (A time, B time, AB time)

8 Repeat steps 1-7 two more times. (If the times for a trial aren't similar to other trials, you

need to re-do it. It's easy to make mistakes with this equipment)

9 Calculate the average times.

10 Calculate the marble's velocity at A, velocity at B and acceleration in 4-point form.

Data:

Marble diameter = x = -0.019 m (? WHY is it negative?)

Time thru photogate A (A time)

photogate A

Trial 1

Trial 2

Trial 3

Average time (s)

Marble's Velocity at A calculation:

photogate B

Time thru photogate B (B time)

Trial 1

Trial 2

Trial 3

Marble's Velocity at B calculation:

Average time (s)

Time marble fell from photogate A to photogate B (AB time)

Trial 1

Trial 2

Trial 3

Average time (s)

4 Acceleration of Marble calculation: (report this on the board for the class)

Class Discussion: 1. Our group letter was ______ Our marble was steel or plastic Our marble's acceleration was________ 2 What is the class average for the acceleration of the heavy steel marble as it falls?

3 What is the class average for the acceleration of the light wood marble as it falls?

4 What does this tell us about how heavy something is and its acceleration when free falling? (take class experimental error into consideration)

Questions to answer: 1 Why was it so important to have the marble fall into the center of the catcher each

trial? (think about x)

2 Do objects fall at a constant velocity or do they speed up or do they slow down? Use your data to support your answer.

3 Do heavy objects fall at the same rate as light objects? Use our class data to support your answer.

4 Galileo dropped a cannon ball and a wooden ball of the same size off the Leaning Tower of Pisa. Which ball do you think hit the ground first?(Cannon ball or wooden ball) Why?

5 Find the % error in your acceleration

Percent error shows how accurate your data collection was by comparing your results to the actual accepted value. Ask me what the accepted value of acceleration is for Columbia MO and find your error. Of course, show all work. I've already put the equation for you. % error = | your answer ? actual answer | x 100

actual answer

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