1. The problem statement, all variables and given/known data In order to configure the equation for the restoring force of a pendulum, my physics book uses this equation: sinθ ≈ θ when the angle is less than π/10 (or about 20 degrees.) I've tried to figure this out on my calculator, but cannot figure out how they make this assumption. 2. Relevant equations The above equation is then put in to Fr = (w)(sinθ) to create this equation: Fr = (w)θ 3. The attempt at a solution Nothing, I have used radians and degrees to try to figure out how they get this equation, but I cannot. Thanks so much for your help!