Calculation of Drag Force against a Cyclist using Python

Objectives:

• Write a Python program to calculate drag force against a cyclist.
• Write a program to plot Velocity vs Drag force
• Write a program to plot Drag Co-efficient vs Drag force.

What is Drag?

In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers (or surfaces) or a fluid and a solid surface.

Coefficient of drag is a dimensionless number that relates an objects drag force to its area and speed, it ranges upwards from 0.

Drag Force Equation:

Fd = 0.5*rho*A*v.^2*cd

where,

rho - Density

A - Frontal Area

v - velocity

cd - drag coefficient

Code: 1

To plot Velocity vs Drag force.

#program to calculate drag force on the cyclist and plot velocity vs Drag force
import matplotlib.pyplot as plt
#inputs

#drag coeff
c_d=0.8

def plot_dragforce_vs_velocity(velocities,drag_force):
	plt.plot(velocities,drag_force,'*-g')
	plt.xlabel('Velocity')
	plt.ylabel('Drag Force')
	plt.title('Velocity vs Drag Force')
	plt.show()

#frontal area
a=0.1

#velocity
velocities=[6,7,8,9,10,11,12]

#density of the air
rho=1.2
drag_force=[]

for v in velocities:
#calculation of drag force
   	drag_force.append((0.5*rho*c_d*a*v*v))

print(drag_force)

plot_dragforce_vs_velocity(velocities,drag_force)

Output:

Code:2

Code to plot Drag Co-efficient vs Drag force.

#Calculation of drag force on a cyclist and plot drag cofficient vs drag force
import matplotlib.pyplot as plt


def plot_dragforce_vs_dragcoefficient(drag_coefficient,drag_force):
	plt.plot(drag_coefficient,drag_force,'*-y')
	plt.title('Drag Coefficient vs Drag Force')
	plt.xlabel('Drag Coefficient')
	plt.ylabel('Drag Force')
	plt.show()

#inputs
#density of air (kg/m^3)
rho=1.2

#velocity of the cyclist  (m/s)
v=1

#frontal area (m^2)

A=0.1

#drag coefficient for various shapes 
drag_coefficient=[0.47,0.42, 0.50 ,1.05, 0.80 ,0.82, 1.15, 0.04, 0.09]

#defining an empty array
drag_force=[] 

#calculation of drag force
for c_d in drag_coefficient:
	drag_force.append((0.5*c_d*A*rho*v*v))

print(drag_force)

plot_dragforce_vs_dragcoefficient(drag_coefficient,drag_force)

Output:

Conclusion: Python program to calculate drag force against a cyclist has been written and required graph are plotted.