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Realistic projectile motion. Newton’s law E total energy of the moving object, P the power supplied into the system.

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Presentation on theme: "Realistic projectile motion. Newton’s law E total energy of the moving object, P the power supplied into the system."— Presentation transcript:

1 Realistic projectile motion

2 Newton’s law E total energy of the moving object, P the power supplied into the system.

3 + O(  t 2 )

4 Initialisation: Set values for P, mass m, and time step  t, and total number of time steps, N, initial velocity v 0. Do the actual calculation v i+1 = v i + (P/mv i )  t t i+1 = t i +  t Repeat for N time steps. Output the result sample code 2.1.1, 2.1.2

5 Frictionless motion is unrealistic as it predicts velocity shoots to infinity with time. Add in drag force, innocently modeled as 2 C ~ 1, depend on aerodynamics, measured experimentally B 2  C  A/2

6 The effect of F drag : P  P – F drag v sample code 2.1.3

7 x y 0 g Wish to know the position (x,y) and velocity (v x,v y ) of the projectile at time t, given initial conditions. Two second order differential equations.

8 Four first order differential equations. Euler’s method Eq Eq. 2.15

9 Drag force comes in via

10 v i = (v x,i 2 +v y,i 2 ) 1/2 i i sample code 2.1.4, , Trajectory of a cannon shell with drag force

11 Drag force on a projectile depends on air’s density, which in turn depends on the altitude. Two types of models for air’s density dependence on altitude: Isothermal approximation - simple, assume constant temperature throughout, corresponds to zero heat conduction in the air. Adiabatic approximation - more realistic, assume poor but non-zero thermal conductivity of air.

12 The drag force w/o correction corresponds to the drag force at sea-level It has to be replaced by

13 Adiabatic approximation:

14 v i = (v x,i 2 +v y,i 2 ) 1/2 i i Trajectory of a cannon shell with drag force, corrected for altitude dependence of air density

15 Modify the existing code to produce the curves as in Figure 2.5, page 30, Giodano 2 nd edition. sample code 2.1.6, , 2.17


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