Hands-on exercise – Function Arguments

Put the lesson Function Arguments into practice by writing a program yourself.

Exercise field

How far does a bar stretch?

The problem

A bar under a tensile force stretches by ΔL = F × L / (A × E), where F is the force (N), L the length (m), A the cross-sectional area (m²) and E the Young's modulus (Pa).

Most bars in your lab are steel (E = 200 × 10⁹ Pa) with an area of 1 × 10⁻⁴ m², so these make good default values.

Your program should

Define bar_extension(force_n, length_m, area_m2=1e-4, modulus_pa=200e9) that returns the extension in millimetres.
Print the extension of a 2 m steel bar under 10,000 N, using the defaults.
Print the extension of the same bar made of aluminium (E = 70 × 10⁹ Pa), using a keyword argument.
Print the extension of the aluminium bar with twice the area (2 × 10⁻⁴ m²), using keyword arguments. Show 3 decimal places each time.

Expected output

Steel: 1.000 mm
Aluminium: 2.857 mm
Aluminium, double area: 1.429 mm

Your solution

Write your program below and press Run. Each run is checked against the expected output.

main.py

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Output

Press Run to see what your program prints.

Need help?

One possible solution. Other programs that print the same output are correct too.

solution.py

def bar_extension(force_n, length_m, area_m2=1e-4, modulus_pa=200e9):    """Elastic extension in mm of a bar under tension."""    return force_n * length_m / (area_m2 * modulus_pa) * 1000print(f"Steel: {bar_extension(10000, 2.0):.3f} mm")print(f"Aluminium: {bar_extension(10000, 2.0, modulus_pa=70e9):.3f} mm")print(f"Aluminium, double area: {bar_extension(10000, 2.0, area_m2=2e-4, modulus_pa=70e9):.3f} mm")

Output

Steel: 1.000 mm Aluminium: 2.857 mm Aluminium, double area: 1.429 mm