Press spacebar to add thrust Explanation: Force is mass times acceleration, The force acting on the bat is the flap force (upwards) minus the gravitational force (downwards) so the acceleration is that divided by the mass of the rocket. The position of the rocket is the double integral of that: x=Δv/Δt v=Δa/Δt a=(F(flap)-m*g)/m The acceleration is the change in velocity, and the velocity is the change in position. So if you change the velocity by the acceleration, and then change the y-position by the velocity you get a realistic representation of real-life physics. The value for gravitational acceleration g is around 9.81 in real-life but for scratch you might need another value for that.