diff --git a/ptx/sec_curvature.ptx b/ptx/sec_curvature.ptx
index df08b0ba1..ecebce505 100644
--- a/ptx/sec_curvature.ptx
+++ b/ptx/sec_curvature.ptx
@@ -208,7 +208,7 @@
We find it with \vec r(2) = \la 1/5, 18/5\ra.
-
+
Graphing \vec r in with parameters t and s
@@ -687,7 +687,7 @@
Being able to think of curvature in terms of the radius of a circle is very useful.
-
+
Illustrating the osculating circles for the curve seen in
@@ -757,7 +757,7 @@
.
-
+
Examining the curvature of y=x^2
@@ -834,26 +834,10 @@
-
- While this is not a particularly nice formula,
- it does explicitly tell us what the curvature is at a given t value.
- To maximize \kappa(t),
- we should solve \kappa'(t)=0 for t.
- This is doable, but very time consuming.
- Instead, consider the graph of
- \kappa(t) as given in .
- We see that \kappa is maximized at two t values;
- using a numerical solver, we find these values are t\approx\pm 0.189.
- In we graph \vrt and indicate the points where curvature is maximized.
-
-
-
-
Understanding the curvature of a curve in space
-
-
-
The curvature of \vec{r}(t)
+
+
The curvature of \vec{r}(t) in
-
+ A plot of the curvature as a function of the parameter t.
@@ -885,11 +869,11 @@
-
-
A plot of the curve \vec{r}(t)=\la t, t^2, 2t^3\ra
+
+
A plot of the curve \vec{r}(t)=\la t, t^2, 2t^3\ra in
-
+ A plot of the vector-valued function in this example, with points of maximum curvature marked.
@@ -950,9 +934,19 @@
-
-
+
+ While this is not a particularly nice formula,
+ it does explicitly tell us what the curvature is at a given t value.
+ To maximize \kappa(t),
+ we should solve \kappa'(t)=0 for t.
+ This is doable, but very time consuming.
+ Instead, consider the graph of
+ \kappa(t) as given in .
+ We see that \kappa is maximized at two t values;
+ using a numerical solver, we find these values are t\approx\pm 0.189.
+ In we graph \vrt and indicate the points where curvature is maximized.
+
diff --git a/ptx/sec_tan_norm.ptx b/ptx/sec_tan_norm.ptx
index 098580294..1638ccfac 100644
--- a/ptx/sec_tan_norm.ptx
+++ b/ptx/sec_tan_norm.ptx
@@ -68,7 +68,7 @@
since they are only length 1.)
-
+
Plotting unit tangent vectors in
@@ -382,7 +382,7 @@
These are sketched in .
-
+
Plotting unit tangent and normal vectors in
@@ -447,17 +447,7 @@
-
+
The previous example was once again
@@ -517,7 +507,7 @@
we compute the unit tangent and normal vectors for t=-1,0 and 1 and sketch them in .
-
+
Plotting unit tangent and normal vectors in
@@ -607,6 +597,18 @@
+
+
+ A brief consideration of this theorem may make one wonder: what if the graph of \vec r does
+ not have a concave side? What if \vec r is a line?
+
+
+ This exposes a shortcoming in our definition of \unitnormal(t), where
+ we require that \unittangent(t) be smooth, i.e., that \unittangentprime(t) \neq \vec 0,
+ a requirement that lines do not fulfill. One may still want to compute a normal vector for a given line, though.
+ For straight lines in the x,y plane, it is most common to orient the normal vector 90^\circ
+ counterclockwise from the tangent vector. For lines in three dimensions, there is no preferred choice of normal vector.
+
@@ -802,7 +804,7 @@
gives a graph of the path for reference.
-
+
Graphing \vec r(t) in
@@ -875,7 +877,7 @@
which we plot in .
-
+
Plotting the position of a thrown ball, with 1s increments shown
@@ -1043,10 +1045,7 @@
If \unittangent(t) is a unit tangent vector,
- what is \norm{\unittangent(t)}?
-
-
-
+ what is \norm{\unittangent(t)}?
@@ -1072,10 +1071,7 @@
If \unitnormal(t) is a unit normal vector,
- what is \unitnormal(t)\cdot \vrp(t)?
-
-
-
+ what is \unitnormal(t)\cdot \vrp(t)?
diff --git a/ptx/sec_vvf.ptx b/ptx/sec_vvf.ptx
index 50ee1a456..a164a0d35 100644
--- a/ptx/sec_vvf.ptx
+++ b/ptx/sec_vvf.ptx
@@ -648,7 +648,7 @@
\vec r(t) = \vec p(t) + \vec c(t) = \la \cos(t) + t,-\sin(t) +1\ra,
which is graphed in .
-
+
The cycloid in
@@ -750,7 +750,7 @@
The displacement of \vec r(t) on [-1,1] is thus \vec d = \la 0,1\ra - \la 0,-1\ra = \la 0,2\ra.
-
+
Graphing the displacement of a position function in
diff --git a/ptx/sec_vvf_calc.ptx b/ptx/sec_vvf_calc.ptx
index e63c127f2..f69815f5f 100644
--- a/ptx/sec_vvf_calc.ptx
+++ b/ptx/sec_vvf_calc.ptx
@@ -19,7 +19,7 @@
The theorem following the definition shows that in practice,
taking limits of vector-valued functions is no more difficult than taking limits of real-valued functions.
-