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{SECT 0 {EXCHG {PARA 0 "" 0 "" {TEXT -1 10 "contact.ms" }}{PARA 0 "" 
0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 274 "A program to illust
rate use of Heaviside functions to model contact between bodies with a
 spring. The spring is attached to the first body, which is moving. Th
e first body strikes the second body, which is at rest. Motions of the
 bodies are then found as a function of time." }}{PARA 0 "" 0 "" 
{TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 92 "x1 refers to the body whi
ch is moving initially. x2  refers to the initially stationary body" }
}{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "> " 0 "" {MPLTEXT 1 0 20 "re
start;with(plots):" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 40 "d:=-x
2(t)+x1(t)+x0; # spring compression" }}}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 44 "eq1:=-k*d*Heaviside(d) = m1*diff(x1(t),t,t);" }}}
{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 46 "eq2:=+k*(d)*Heaviside(d) = m
2*diff(x2(t),t,t);" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 32 "value
s:=\{m1=1,m2=1,k=10,x0=1/2\};" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 
0 39 "eqs:=subs(values,eq1),subs(values,eq2);" }}}{EXCHG {PARA 0 "> " 
0 "" {MPLTEXT 1 0 77 "s:=dsolve(\{eqs,x1(0)=0,D(x1)(0)=5,x2(0)=1,D(x2)
(0)=0\},\{x1(t),x2(t)\},numeric);" }}}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 39 "h:=odeplot(s,[t,x1(t)],0..1,color=red):" }}}{EXCHG 
{PARA 0 "> " 0 "" {MPLTEXT 1 0 40 "j:=odeplot(s,[t,x2(t)],0..1,color=b
lue):" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 52 "display(\{h,j\},ti
tle=`x1(t)[red], x2(t)[blue] vs t`);" }}}{EXCHG {PARA 0 "> " 0 "" 
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