Department of Astronomy & Physics
Dr. Adam Sarty has received one of ten 3M National Teaching Fellowships. Later this year Dr. Sarty will be inducted into the Society for Teaching and Learning in Higher Education.
Dr. Sarty is about to demonstrate that all objects near the earth's surface fall to the ground at the same rate. Everyone knows that a feather and ball bearing will not fall at the same rate but this is because air friction slows the descent of the feather more than the ball bearing. If you compare the rate at which a feather and a ball bearing fall in a vacuum, you will discover that they do indeed fall to the ground at the same rate.
Why is this so? Undergraduate level physics explanation: it's because the inertial force (F=ma) and the gravitational force (GmM/r^2) both depend on the mass of the object, m, and the mass cancels out. Graduate level physics explanation: experiments show inertial mass is equal to gravitational mass to within experimental uncertainties but we do not have a theory of mass and gravity (quantum gravity) that explains why the two should be equal, i.e., we don't know why.
Apollo 15 Commander David Scott dropped a hammer and a feather on the surface of the moon. You can see what happened here.