**HP Prime: Free Fall with Air Friction **

**Introduction**

The program FALLS will calculate the position and velocity of an object falling with friction proportional to square of the object's speed. The program is aimed towards large objects in free fall. The half-increment method is used.

With the initial conditions:

y = 0 (initial position, assumed to be at zero)

g = gravitational constant

α = f/m (force-mass ratio)

dy/dt = 0 (velocity, assume to be at rest from the beginning)

With Δt with the change of time:

dy/dt_1/2 = dy/dt_0 + C * Δt/2 where C = g - α * (dy/dt_0)^2

dy/dt_(i+1/2) = dy/dt_(i-1/2) + C * Δt where C = g - α * (dy/dt_(i-1/2))^2

y_i+1 = y_i + dy/dt_(i+1/2) * Δt

**HP Prime Program: FALLS**

**EXPORT FALLS()**

**BEGIN**

**// EWS 2022-11-03**

**HFormat:=1;**

**HDigits:=4; **

**LOCAL t,g,a,n;**

**LOCAL i,d,c,y,m;**

**LOCAL l0,l1,l2;**

**LOCAL l3,l4,m0;**

** **

**INPUT({t,g,a,n},"Fall-Air Resistance",**

**{"Δt =","g =","α =","n ="},**

**{"charge in time","gravity",**

**"force/mass","number of steps"});**

**l0:={m};**

**l1:={d};**

**l2:={y};**

**// for section here**

**FOR i FROM 1 TO n DO**

**c:=g-a*d^2;**

**IF t==0 THEN**

**c:=c/2;**

**END;**

**d:=d+c*t;**

**m:=m+t;**

**y:=y+d*t;**

**l0:=CONCAT(l0,{m});**

**l1:=CONCAT(l1,{d});**

**l2:=CONCAT(l2,{y}); **

**END;**

**l3:=CONCAT(l0,l1);**

**l4:=CONCAT(l3,l2);**

**m0:=list2mat(l4,SIZE(l0));**

**m0:=TRN(m0);**

**RETURN m0;**

** **

**END;**

The result is a matrix wit the columns:

Column 1: time (t = m)

Column 2: velocity (dy/dt = d)

Column 3: position (y)

The program assumes that the object or person being dropped is well above the ground or floor.

**Example**

Go 10 steps with Δ = 0.25 sec, g = 9.80665 m/s^2, and α = 0.028

Velocity ≈ 18.6716 m/s

Position ≈ 76.1314 m

The program assumes that the object or person being dropped is well above the ground or floor.

Source

Eisberg, Robert M. __Applied Mathematical Physics with Programmable Pocket Calculators__ McGraw-Hill Book Company: New York 1976. ISBN 0-07-019109-3

**I want to wish you a Happy New Year. May you have a healthy, prosperous, and happy 2023!**

Note: For January and February 2023, my posting schedule will be on Saturdays only, starting January 7. This doesn't include any firmware updates or reviews, they will be on Mondays should they occur. One of my resolutions for 2023 is to catch up on my reading of math books and articles.

Eddie

All original content copyright, © 2011-2022. Edward Shore. Unauthorized use and/or unauthorized distribution for commercial purposes without express and written permission from the author is strictly prohibited. This blog entry may be distributed for noncommercial purposes, provided that full credit is given to the author.