Motion simulation of a point and a circular object

Question

Theo James 2017-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/346886-motion-simulation-of-a-point-and-a-circular-object

回答： Veronica Maria Rodriguez Betancourtt 2021-5-29

Matlab beginner checking in. I've written some code for a point moving in a straight line with a constant velocity (for a given initial position and velocity). Could anyone tell me how to get rid of the trace created as the point moves?

   pC = [4; 10];                          % initial position of A
   vC = [2.3100; -0.5500];                % initial velocity of A
   dt = 0.1;                              % time step for animation
   clf;                                   % Clear the figure 
   axis(50*[0 1 0 1],'square');           % Set axis limits
   grid on;
   hold on;                               % Keep plot from erasing
     for t=0:dt:15                        % t is time variable 
        plot(pC(1),pC(2),'ro')            % Plot circle
        pC = pC + vC*dt;                  % update position
        pause(dt)                         % pause for animation
     end
   hold off;
   title('Motion animation');
   xlabel('x (m)');  
   ylabel('y (m)');

In the same plot, I need to simulate a circular object undergoing uniform circular motion with constant speed (given position of center of circular path, radius of circular path, initial position of center of circular object, radius and tangential velocity of circular object). Any advice?

pA = [22; 8];                   % position of center of circular path
rA = 4;                         % radius of circular path
pB = [25.8637; 9.0353];         % initial position of B
vB = [-0.5176; 1.9319];         % tangential velocity of B
rB = 1;                         % radius of B

I've attached a picture for clarity.

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Answer 1

KSSV 2017-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/346886-motion-simulation-of-a-point-and-a-circular-object#answer_272481

编辑：KSSV 2017-6-30

在 MATLAB Online 中打开

vA = [2.31; -0.55];                    % initial velocity
dt = 0.1;                              % time step for animation.
% get points trajectory 
t = 0:dt:10 ;
pA = zeros(2,length(t)+1) ;
pA(:,1) = [4 ;10] ;   % initial position 
for i = 2:length(t)+1                        % t is time variable
%     plot(pA(1),pA(2),'ro')            % Plot circle
    pA(:,i) = pA(:,i-1) + vA*dt;            % update position
end
% plot
figure
title('Motion animation');
xlabel('x (m)');
ylabel('y (m)');
h = plot(pA(1,1),pA(1,2),'Or') ;
axis([min(pA(1,:)) max(pA(1,:)) min(pA(2,:)) max(pA(2,:)) ])
for i = 1:length(pA)
    set(h,'XData',pA(1,i),'YData',pA(2,i))
    pause(0.05)
end

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Theo James 2017-6-30

The comet function still leaves a trail behind. I'm actually trying to get rid of it. Also, would you happen to have the answer to my second part?

KSSV 2017-6-30

code edited....

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Answer 2

Veronica Maria Rodriguez Betancourtt 2021-5-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/346886-motion-simulation-of-a-point-and-a-circular-object#answer_712465

在 MATLAB Online 中打开

clear
dt = 0.1;                       % time step
t = 0:dt:12 ;                   % time
pR=zeros(2,length(t));pB=zeros(2,length(t));
pR(:,1) = [4 ;10] ;             % initial position of R ("Red dot")
vR = [2.31; -0.55];             % initial velocity of R
pB(:,1) = [25.8637; 9.0353] ;   % initial position of B ("Blue dot")
vB = [-0.5176; 1.9319];         % tangential velocity of B
pC = [22; 8];                   % position of circular path's center
rC = 4;                         % circular path's radius
th=zeros;th(1)=atan(pB(2)/pB(1));
for i = 2:length(t)                        
    pR(:,i) = pR(:,i-1) + vR*dt; % R's position update ([x y])
    th(i)=th(i-1)+norm(vB)*dt/rC; % th: angle,
                                  % norm(vB)/rC = angular velocity
    pB(:,i) = pC + rC*[cos(th(i));sin(th(i))]; % B's position update 
end
% Plotting:
h1 = plot(pR(1,1),pR(2,1),'Or') ;grid on, hold on
h2 = plot(pB(1,1),pB(2,1),'Ob');
title('Motion animation');xlabel('x (m)');ylabel('y (m)');
% axis([min(pA(1,:)) max(pA(1,:)) min(pA(2,:)) max(pA(2,:)) ])
axis([4 26 4 12])
plotcircle(rC,pC(1),pC(2))    % B's path
for i = 1:length(pR)
    set(h1,'XData',pR(1,i),'YData',pR(2,i))
    set(h2,'XData',pB(1,i),'YData',pB(2,i))
    pause(0.05)
end
function plotcircle(r,x,y)
% https://www.mathworks.com/matlabcentral/answers/...
% 98665-how-do-i-plot-a-circle-with-a-given-radius-and-center
plot(r*exp(1i*(0:pi/100:2*pi))+x+1i*y,'--');
end

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Answer 3

Sandy Narsale 2018-10-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/346886-motion-simulation-of-a-point-and-a-circular-object#answer_339323

在 MATLAB Online 中打开

MATLAB Answers™ Theo James 0 Flag Motion simulation of a point and a circular object Asked by Theo James on 30 Jun 2017 Latest activity Edited by KSSV on 30 Jun 2017 113 views (last 30 days) Matlab beginner checking in. I've written some code for a point moving in a straight line with a constant velocity (for a given initial position and velocity). Could anyone tell me how to get rid of the trace created as the point moves?

   pC = [4; 10];                          % initial position of A
   vC = [2.3100; -0.5500];                % initial velocity of A
   dt = 0.1;                              % time step for animation
   clf;                                   % Clear the figure 
   axis(50*[0 1 0 1],'square');           % Set axis limits
   grid on;
   hold on;                               % Keep plot from erasing
     for t=0:dt:15                        % t is time variable 
        plot(pC(1),pC(2),'ro')            % Plot circle
        pC = pC + vC*dt;                  % update position
        pause(dt)                         % pause for animation
     end
   hold off;
   title('Motion animation');
   xlabel('x (m)');  
   ylabel('y (m)');
In the same plot, I need to simulate a circular object undergoing uniform circular motion with constant speed (given position of center of circular path, radius of circular path, initial position of center of circular object, radius and tangential velocity of circular object). Any advice?

pA = [22; 8]; % position of center of circular path rA = 4; % radius of circular path pB = [25.8637; 9.0353]; % initial position of B vB = [-0.5176; 1.9319]; % tangential velocity of B rB = 1; % radius of B I've attached a picture for clarity.

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1 Answer
KSSV
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Answer by KSSV  on 30 Jun 2017
Edited by KSSV  on 30 Jun 2017

vA = [2.31; -0.55]; % initial velocity dt = 0.1; % time step for animation. % get points trajectory t = 0:dt:10 ; pA = zeros(2,length(t)+1) ; pA(:,1) = [4 ;10] ; % initial position for i = 2:length(t)+1 % t is time variable % plot(pA(1),pA(2),'ro') % Plot circle pA(:,i) = pA(:,i-1) + vA*dt; % update position end % plot figure title('Motion animation'); xlabel('x (m)'); ylabel('y (m)'); h = plot(pA(1,1),pA(1,2),'Or') ; axis([min(pA(1,:)) max(pA(1,:)) min(pA(2,:)) max(pA(2,:)) ]) for i = 1:length(pA) set(h,'XData',pA(1,i),'YData',pA(2,i)) pause(0.05) end