Eric Murray, Spring 2006
Newton's First Law states that an object on which there is no net force must have an acceleration of zero. You will examine an object whose acceleration is zero by inspection. That is, you will be able to observe that its velocity is constant, namely, the constant zero. This object, which may be a small plastic ring or simply a knot, is subject to three distinct horizontal forces. According to Newton's First Law, these three forces must add to zero. By adding the three forces as vectors, you will determine if the net force is, in fact, zero.
You may wish to review vector algebra in section 3.4 of Knight's Physics for Scientists and Engineers.