# Lab 4 Free Fall

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```					DSHS Physics Mathy                                                               DO NOT WRITE ON THIS!!!!!
Lab#4 Acceleration (g)
Chapter 2

Formal Lab #4 Free Fall Made Easy
Free Fall Explained
You have learned in your science class that all objects (if air resistance is excluded from the mix) accelerate at the exact same
rate, - 9.8 m/s . But how do we know that for certain? Now that we are familiar with the equation dy= vit + 1/2gt we will set out
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to verify that number! Let’s assume that humans have not discovered the value of “free falling acceleration” yet. The goal is to
use only a meter stick, a stopwatch, and a tennis ball, and from these three items ; calculate the value of acceleration due to
gravity ( g) on planet earth with some degree of accuracy.

Purpose :To discover a practical way to measure acceleration due to gravity on earth from the relationship between time and
displacement of a falling object

Hypothesis: If we know the mathematical equation for constant acceleration, we can use a graph to calculate acceleration due
to gravity in multiple ways.

Materials to be used:
Stop Watch
Meter stick
Tennis ball

Illustration : This is to be created by you!

Write Procedures and Data in your Lab Book
You will now write out your own procedures for how your group accomplished its objective. Be sure to include an explanation of
how you calculated the results, number of trials you used (use lots!!) , and create a data table that will aid in showing how you
collected your data! Hint : Drop the ball from multiple heights !

Graphing Section

You will need to create two separate graphs in your graphing section using the Excel graphing program.

Graph #1 Displacement (doubled) vs Time Squared

As a quick review:
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Create an XY SCATTER style graph by plotting 2 times the displacement (2x) vs. time squared (t ). Normally, the x-
axis should be your independent variable( i.e. what you manipulated). However, for this lab we will put the
displacement dimension on the y axis and the time dimension on the x axis.
    Highlight your data then select GALLERY>CHART>XY SCATTER>MARKED SCATTER
    Give your chart a title and label the x and y axes ( include units!) from the Formatting Palette on the right side
    To add the trend line, start by clicking on a data point then going to CHART> ADD TRENDLINE.

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Finally, put the slope equation and R value on your graph under trend line OPTIONS > DISPLAY EQUATION & R

Paste your graph in the open space of a word document now, shrink it !

Now create a Graph #2 for Displacement vs Time. Repeat the steps for trend line etc.

1. Using the data you collected, calculate the acceleration due to gravity using the equation provided on this lab sheet (e.g.
solve “gravity “ as the unknown). Since you used multiple heights, you will have multiple values. Show your work for these
calculations in your lab book. It is acceptable to use the average of all times from one height.
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2. The true value for gravity on earth is -9.81 m/ s here at DSHS . Your experimental value for gravity for this lab will be an
average for all of the values for g you calculated. From this number, Calculate a percentage of error based on the actual value
for gravity. The P.O.E. equation is in your lab book!

continue

3. List the mathematical value for the slope of Graph #1. This would be the “m” in y=mx + b .
Slope : _____________

a) The slope will also reveal the units for this value. List the units for the slope : ___________

4. Based on the above information, what is the physical meaning of slope of this graph pertaining to the lab?

5. Using algebraic variables, solve for “g” from the equation d= vit + 1/2gt ( hint: don’t use actual numbers)
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6. Relate the variable “g” to your graph you made in Excell of 2d vs t . What is the connection?

7. Refer to Graph #2 and describe the mathematical equation that created it (e.g. y= ?) .

b) What concept does the slope represent for this lab ?

Now….go to the motion sensor stations and create one V vs T graph by dropping a soft Nerf ball to the sensor. Stretch the x
and y-axis until you have at least three data points that look reasonable. Draw this graph with the axes labeled correctly and

8. What does the slope of this new graph represent? How does this compare with the graph created with Excel?