Measuring the Drag Force on a Falling Ball

The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is usually small compared with the gravitational force if the object mass is large and its speed is low. In order to observe a significant effect, or to measure the terminal velocity, experiments are often conducted with very light objects such as a balloon^1,2 or coffee filter³ or muffin cup,⁴ or are conducted in a liquid rather than in air. The effect of the drag force can also be increased by increasing the surface area of the object.