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+/-

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Axis Convention: you can define the + direction as up or down. You’re in charge; it’s up to you. Your decision will affect the appearance of graphs. You can change this at anytime.
∆time (s): indicates the time increment at which calculations are performed. Smaller values mean greater accuracy but more data.
Init. Height (m): the object must start above the ground. The initial height indicates the distance above the ground when t = 0.0 seconds.
Init. Velocity (m/s): the object can be dropped from rest, projected upward, or project downward. This information is conveyed by the value of the initial velocity (the velocity at t = 0.0 seconds).
g (N/kg): choose the value for the gravitational field constant. Run your experiment on Earth or take a field trip to the moon (or wherever).
Mass (kg): identify the mass of your object.
Profile Area (m2): this is the projection of the object onto a horizontal plane. Estimate it … intelligently.
Drag Coefficient: this unit-less coefficient provides a measure of how efficiently the air streams around the object. Use the Wikipedia page to assist in obtaining an estimated value for your object.
Air Density (kg/L): the density of air through which the object is falling. The program assumes this value to be constant. Use the Wikipedia page to provide an estimated value.
Additional information is available at our website.
Tap anywhere to close.

This program models the falling motion of an object in the presence of air resistance. Parameters can be changed and their effect on the motion is immediately observed. The currently used parameter values are listed above. The Change Parameters button allows you to modify values.
There are two “outputs” - data and graphs. Use the Up and Down arrows to scroll through the data. Look for patterns in the data, inspecting multiple columns for the same time period. The View Data and View Graphs buttons can be used to toggle between the two display outputs. There are multiple graph options. Use the buttons to the right of the graph to alter the quantities being graphed.
Data should be interpretted in light of your axis conventions for + and - signs. Sometimes a value of -0.000 is reported. This usually means the value is something like -0.000352 and the last digits are not displayed.
The ∆t value is an important parameter. A large value (0.05 and greater) results in inaccuracies (especially for low initial heights). Too small of a (0.01 and smaller) results in excessive amounts of data (especially for tall initial heights). For initial heights greater than 5000 m, a value of 0.1 works well. For initial heights less than 500 m, a value of 0.01 or smaller works well.
Values of the drag coefficient should be estimated based on object shape. The Wikipedia page is a good resource for making an estimate.

hideHolders

Data:

Parameters:

∆t (s)

This is the top of the table.

Change Parameters

.1

View Data

vi (m/s)

View Graphs

0

g (N/m)

∆time (s):

-9.8

m (kg)

Axis Convention:

80.0

t (s)

hi (m)

g (N/kg):

Ht (m)

Parameters

Down is + … Up is -

5000

v (m/s)

Quantity: Value

a (m/s2)

Change

Fair (N)

Fnet (N)

Init. Height (m):

A

View Wikipedia page
for guidance.

Mass (kg):

Constraints

0

Air Dens. (kg/L):

Minimum Value: 0.001 s

C

Must be > 1 m

2

Init. Velocity (m/s):

Notice
Sign!!

9

Values for the following eight parameters are required to model a falling object. Enter the values directly into the field OR tap on the Number Pad icon to use our built-in number entry pad. Tap the Info icon (above right) for information about their meaning. When all values have been entered, tap on the Model Motion button.

Profile Area (m2):

Use of +/- sign must
follow axis convention.

1

8

Model Motion

v vs. t

Once done, tap the
Close button.

7

Minimum Value: 1 kg

Back Space

a vs. t

Drag Coefficient:

Fair vs. t

Must be > 0 m2

6

Use the Number Pad to enter the value of ...

Fnet vs. t

View Wikipedia page
for guidance.

5

A (m2)

.

Display 3 Graphs

0.80

Close

4

Cdrag

Display 4 Graphs

0.50

3

dens (kg/L)

1.25

h vs. t

Falling Bodies
in 1-Dimension

Version 1.1

Model the real-world motion of a falling object in the presence of air resistance. Identify and modify parameters and explore a What if …? question.

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