The gate across the footbridge below Low Nest Farm was very stiff. I can lift my whole body weight with one leg but an arm is weaker. Say I can push with a force of 200N. We can work out the force on the spring by equating moments measuring the distance from the hinge. Spring to hinge is about 3cm and hand to hinge is 30cm. This gives a force on the spring of 2000N. If the spring obeys Hooke's Law then force = spring constant x extension. Spring constant is how many Newtons of force the spring needs per unit extension. It used to be called the stiffness of the spring and sometimes gets called the stiffness constant on exams. F=ke. So k=F/e. If the extension of the spring is 10cm or 0.1m so k=2000/0.1 = 20000 N/m.
