Click or press spacebar, play with the variables to get the result you want. Trust me, I'm an engineer. 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 devided by the mass of the bat. The position of the bat 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.
Made for https://scratch.mit.edu/projects/196156228/, the scratch education studio and the Core Programming for Physics Simulation studio. It might be a bit slow in the beginning because it has to load the background gif, but after a second or two it should work fine. https://scratch.mit.edu/statistics/ shows that most scratchers are around 13 years old. At that age you haven't (and shouldn't have) had a lot of education about forces, acceleration, integrals etc. although you need that to make realistic game mechanics. If you want to, you can embed this project into your own. Credits would be nice, but are not necessary.