Equilibrium of Rigid Bodies (Part II)
Introduction
The object is in equilibrium, when sum of all forces operating on this object, is equal to zero. That means that the object has no any forces which make it rotate or being unsteady. According to Newton’s 3rd law, each action has counteraction which has same force, but directed to opposite direction. Force of reaction, is that kind of force, which keeps an object to be in equilibrium without participation of surrounding forces. As an example to it, the object which lies on the flat surface can serve. The object operates on a surface and a surface operates on object with the same force. Force with which object operates on a surface passes through its centre of gravity and perpendicular to the surface. Force of the reaction also passes through the centre of gravity of the object. Thereby, it is possible to confirm that the object which lies on the flat surface, without surrounding forces, is in equilibrium. Hence, if the force acting on object does not pass through its centre, when object is in equilibrium, the object will start to rotate aside to which force is directed. The reason for it, is the momentum. Momentum can be defined by the formula:
Where
is the force that acting to object, and
is the distance between centre of gravity of the object and the
acting force.
The experiment is made from two different objectives. Idea of the experiment is using the system if objects, which are in equilibrium, is to learn how to use and how balancing is important for. The first objective is to find the mass of the unknown object using balanced system of known objects and one metre ruler. For that part we should know at least one known mass, which will be used, to find the mass of the unknown object or objects. The second part of the experiment is to find the mass and the centre of gravity of two irregular shaped bars, using at least two known masses.
Experimental Procedure
Apparatus:
Metre ruler, iron stand, triple beam balance, set of masses, light string, unknown masses and irregular shaped bars.
Object 1
In this object, originally, we need to find the mass of the one unknown object using at least one known mass and one metre ruler, which hanged on the iron stand. In my experiment I have used two unknown masses and one known mass. As unknown masses were used pen and block, as the known mas was used mass of the 50 gram. Hence, experiment has been made two times to get enough information for determination of the unknown masses. That means in different times, objects had different places on the ruler. First of all will be shown and explain each part of the Object 1. Then, will be shown Table, which includes all raw data.
Part A (Experiment 1 explanation)
First of all, will be explained how all system were set up. In the beginning iron stand was connected to the triple beam balance. Then, using light string, one metre ruler was connected to the iron stand. After that, one metre was fixed in the point 48.8cm, which is the centre of mass of the ruler. When one metre ruler was in equilibrium, I started to hang objects. One known object and pen were hanged to the right side, and block was hanged to the left side. Then I found for that objects special places, where system was in equilibrium and did not shacked or moved.
The Figure 1 below is showing how experiment was set up.