Help with gravity animation!

Hi,

I have been using MATLAB for a couple weeks now and I would love to try to animate something to do with gravity.

I have tried to animate a line (e.g. canonball) thrown starting from x = 0 and y = 0, (0,0), with a beginning velocity and throwing angle.

I tried to animate the line starting from (0,0) until it hits the ground but when I save and press Run, the figure opens but nothing happens.

Can someone help me understand what I am doing wrong? I have no clue what I am doing.

function animation = gravity()

g = 9.82;    %g-constant
v0 = 35;     %starting velocity
alpha = 50;  %angle
picNr = 0;  %picture number starts at 0 (for animation)


y = @(t)v0*t*sind(alpha)-0.5*g*t.^2; %throwing motion y-axis
x = @(t)v0*t*cosd(alpha);       %throwing motion x-axis (constant velocity)

T = v0*sind(alpha)/(0.5*g);   %time it takes for the "ball" to hit the ground



for t = linspace(0,T,100)
    
    picNr = picNr + 1;
    
    plot(x(t),y(t),'b--','LineWidth',5,'MarkerSize',12);
    axis([-5 150 -5 45]);
    
    animation(picNr) = getframe;
end

Any help would be deeply appreciated!

Answer 1

[Image Analyst]

Try this:

g = 9.82;    %g-constant
v0 = 35;     %starting velocity
alpha = 50;  %angle

T = v0*sind(alpha)/(0.5*g);   %time it takes for the "ball" to hit the ground

t = linspace(0,T,100);
y = v0*t*sind(alpha)-0.5*g*t.^2; %throwing motion y-axis
x = v0*t*cosd(alpha);       %throwing motion x-axis (constant velocity)

for k = 1 : length(t)
    plot(x(1:k),y(1:k),'r--','LineWidth',2);
    hold on;
    hPlot = plot(x(k),y(k),'b.','LineWidth',5,'MarkerSize', 50);
    axis([-5 150 -5 45]);
    caption = sprintf('Frame %d of %d', k, length(t));
    title(caption);
    drawnow;
    grid on;
    pause(0.2);
    delete(hPlot); % Clear last marker
end
grid on;
g = gcf;
g.WindowState = 'maximized'

[abbyeit]

WOW! Thank you so much!

I have been playing around with this code for the past 2 days you helped me with, learning alot!

I've tried simplifying to a point where it was simple enough for me to understand, but while the code still worked.

I have tried making the ball go out at a randomised angle, and then created another animation in the same for-loop where another ball also plays at the same time, it works!

This is the code I have come up with so far:

g = 9.82;    
v0 = 35;     
alpha = rand(1)*180;              %randomized angle for ball 1
beta = rand(1)*180;               %randomized angle for ball 2 

  
t = linspace(0,15,150);           %time

y1 = v0*t*sind(alpha)-0.5*g*t.^2;  %variables/equation for ball 1
x1 = v0*t*cosd(alpha);             


y2 = v0*t*sind(beta)-0.5*g*t.^2;   %variables/equation for ball 2
x2 = v0*t*cosd(beta);


for k = 1 : length(t)

    plot(x1(1:k),y1(1:k),'r--','LineWidth',2);     %plotting ball 1
    hold on;
    
    plot(x2(1:k),y2(1:k),'g--','LineWidth',2);     %plotting ball 2
    hold on;

    aPlot = plot(x1(k),y1(k),'b.','LineWidth',5,'MarkerSize', 50);
    
    bPlot = plot(x2(k),y2(k),'k.','LineWidth',5,'MarkerSize', 50);
     
    
    pause(0.015);
    
    delete(aPlot); % Clears last marker ball 1
    delete(bPlot); % Clears last marker ball 2
    
    axis([-150 150 -45 45]);
    
end

clear; clc; 

The goal with this code is to eventually be able to make the balls attract/gravitize to one another after being thrown out and then becoming "one" ball/planet, sort of like "BigBang", rather than the balls just falling down. I was thinking that maybe it would work with Newton's Law of Gravity formula, but I am not sure. Would you know how to code/approach such an animation?

You CERTAINLY have helped me tremendously already and definitely you should not feel obligated to help me further.

Again, thank you so much for the code!

[Image Analyst]

I'll let you do the thought and modifications necessary to add gravity between the projectiles - I'd just have to do the same thing so I'll let you do it since it's your problem.

Another demo I can offer is my projectile demo that computes just about everything you could want to know about a projectile (assumes no drag). It's attached.