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# Excel simulations

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*Free fall*: [ video] spreadsheet background, more

*Flight of a cannonball*: This is a story often repeated: in the middle ages people thought that cannonball follows a trajectory made of two straight lines, a sloped climb and followed by a vertical drop. True or not, this simulation shows how the person standing behind the cannon might get this impression. video spreadsheet background

*Breakwater*: We show a simulation of a breakwater protecting a harbor. It starts with a single “pulse” (tsunami?) outside the harbor, $u(20,3,0)=1$, and $u(x,y,0)=0$ for the rest of $(x,y)$, and $u(x,y,1)=0$ for all $(x,y)$. The breakwater is represented by a row of fixed values: $u(x,10,t)=0$ for all $x\ne 20$, with a single gap. The large waves outside produce very mild, circular waves inside. video spreadsheet background

*Drum*: A drum is a circular membrane the edge of which is attached to a ring. In other words, the boundary condition is $u(x,y,t)=0$ when $(x,y)$ is on the circle. We choose the initial shape of the drum to be a rotated sinusoid and zero initial velocity. video spreadsheet background

*Heater in the middle of a room*: For each t, our function $u(⋅,⋅,t)$ is a function of two variables and can be visualized by its graph. For example, a square heater in the middle of a room will produce the following dynamics of distribution of the temperature over the floor. video spreadsheet background

*Room with hot and cold walls*: Heat transfer in a room with two cold and two warm walls. video spreadsheet background

*Pendulum*: The clip demonstrates the physics of a pendulum. It’s implemented with Excel and you can see how things are computed: the gravity (green), its projection on the string (purple), the tangential component of the force (red), the acceleration, the velocity, and finally the location. video spreadsheet background

*Traveling wave*: The simulation starts with an arbitrary shape given by the first initial condition $u(x,0)$. It is a small piece of a sinusoid. The second initial condition is just a shift, $u(x,1)=u(x−1,0)$, of the first. The simulation continues to produce this shift at every iteration; in fact, the magnitude of the initial shift is the speed of propagation of the shape. The rope behaves like a whip. This effect is known as a “traveling wave”. video spreadsheet background

*Unstable wave simulation*: Same as above but failed because of a bad choice of parameters. video spreadsheet background

*Two-body problem*: The clip demonstrates the effects of mutual gravitation of two bodies of comparable mass. It’s implemented with Excel and you can see how things are computed: the location, the net force, the acceleration, the velocity, and the new location. video spreadsheet background

*Vibrating string*: The simulation starts with a sinusoid given by the first initial condition $u(x,0)=\sin(\pi x/n)$. The second initial condition is an exact copy, $u(x,1)=u(x,0)$, of the first. The initial velocity, then, is zero (there is of course acceleration). The simulation produces more sinusoids and a perfect vibration. video spreadsheet background

*A solar system*: You can see how things are recursively computed: the mutual gravity force from the locations, the accelerations, the velocities, and finally the updated locations. The solar eclipse is also shown. video spreadsheet background