Definition
Center of gravity of an object is the imaginary point where the entire weight of the object seems to act #PhysicsDefinitions
For object to be in balance ⇒ sum of clockwise moments due to individual particles must be equal to sum of anticlockwise moments. ⇒ equivalent to having force acting through a point below pivot, since net turning effect is 0.
⇒ can also represent sum of all individual particles weight by a resultant force acting through this point. Resultant force is the weight of the body
Centre of gravity of an object ⇒ that has regular shape and density ⇒ is at centroid or centre of object
NOTE: Centre of gravity does not need to lie within the object. example is with ring
Finding Centre of Gravity of Irregularly Shaped Object
MEMORISE*
- Make small holes near edges of the lamina
- holes should be as far away as possible
- suspend lamina freely from a pin. lamina will come to rest when centre of gravity is below the pin.
- Hang a plumb line from pin in front of lamina
- mark top and bottom of plumb line on lamina
- Repeat for the other holes
- Place lamina on the table and join the markings
Centre of gravity ⇒ is point of intersection of lines you have drawn before. (for some irregularly shaped lamina ⇒ point of intersection lies outside Lamina Itself)
Precautions
- switch off fans ⇒ wind may affect equilibrium position of lamina
- use a thin thread for plumb line
- ensure plumb line is not swinging when marking the point
- ensure that the holes on the lamina are small but still allow lamina to swing freely. Frictional force between pin and lamina may affect equilibrium position