Centre of Mass
In this article we are going to learn about centre of mass, performing and describing an experiment to determine the position of the centre of mass of a plane lamina. describe qualitatively the effect of the position of the centre of mass on the stability of simple objects.
Definition of terms:
Centre of mass or centre of gravity: is a point at which the mass of a body seems to be concentrated at and the body’s weight can be considered to act at this point even though the Earth attracts every part of it.
Centre of mass of a plane lamina:
Experiment to find centre of mass of a plane lamina
Materials: lamina (irregular paper), nail, thread, weight (object), stand, ruler and pencil.
Step 1: Make a hole A in the lamina.
Step 2: Hang lamina so that it can swing freely on a nail clamped in a stand and wait for it to be at rest.
Step 3: Tie a plumb line (a thread and a weight) to the nail.
Step 4: Draw a straight line along thread using a ruler and mark line (plumb line) A and B with a pencil.
Step 5: Repeat step 1, 2, 3 and 4 at a different point and mark line C and D with a pencil.
Step 6: Make a point where two lines intersect. This point is the centre of mass of a plane lamina.
Stability and three States of equilibrium:
1. Stable equilibrium: A body is in stable equilibrium if when slightly displaced and then released it returns to its previous position.
2. Unstable equilibrium: A body is in unstable equilibrium if it moves further away from its previous position when slightly displaced and released.
3. Neutral equilibrium: A body is in neutral equilibrium if it stays in its new position when displaced. Its centre of mass does not rise or fall because there is no moment to increase or decrease the displacement.
Ways to increase stability of a body:
(a) Lowering its centre of mass.
(b) Increasing the area of its base.