Users' Guide User guide

118 Newton’s Law of Cooling
Analysis
Observe the graph of Object Temperature versus time and Air Temperature ver-
sus Time. If the experiment were allowed to run indefinitely, what would the
relationship between object and air temperature eventually be?
1. Create a calculation for relative temperature.
a) Press to return to the Home Screen; press to open the Calcu-
lator.
b) If you see the Num Lock symbol in the lower right corner of the
screen, press to open the Edit menu, then press to turn Num
Lock off.
c) Enter:
° °
Use multipress text entry to type “r”.
To insert [object temp (°C)] and [air temp (°C)] press to open the
[Data] menu, select the desired data from the menu, and select units of
°C.
d) Remember to press to complete the calculation.
2. Make a new graph of r versus t.
a) Press to return to the Home Screen; press to open the Graph.
b) Press to open the Graphs menu; press to select New Graph
Page.
c) Press twice to open the data source menu. Select r from the menu.
3. Does the graph of Relative Temperature versus Time appear to agree
with Equation 2?_______________
4. What is the initial relative temperature at Time = 0?
To find the initial relative temperature, press the up arrow key to move
the Data Cursor to the first data point.
Initial temperature, r
0
= __________
In order to find the value of the constant k for this cooling curve, you can use
another expression of Newton’s Law of Cooling, derived from Equation 2:
(eq. 3)
On a graph of ln(r/r
0
) versus t, the slope will equal −k.
F2
Open the [Data] menu and select
the desired data to insert into the
calculation
F3
F4
1pqrs
F2
F1
F4
7 ?!
Press the up arrow to
move the Data Cursor to
the first data point.
Coordinates of
Data Cursor
ln
r
r
0
----
kt–=