11th physics lesson

1. Dr.M. ANNIE FREEDA
P.G Assistant in PHYSICS
S.L.B.G.H.S.S., NAGERCOIL
Kanyakumari District
CENTRE OF MASS

2. CENTRE OF MASS
. We could see a large number of objects around us.
. Objects around us consists of large number of particles.
. When an object moves collection of all particles as a system
moves.
. To understand the concept of centre of mass we must know.
1) What is a rigid body.
2) What is a point mass
3) What path does the particles in a body take, while
the body moves

3. A rigid body is the one which maintain its definite and
fixed shape even when an external force acts on it
A point mass is a hypothetical point particle which has
nonzero mass and no size or shape.

4. Let us consider a solid cylinder hollow
cylinder and a sphere moving
Rolling objectsNew folderVID20180816190739.mp4
Rolling objectsNew folderVID20180816191621.mp4
Rolling objectsNew folderVID20180816192031.mp4

5. When a bulk object (say a bat) is thrown at an
angle in air
Actually, only one point takes the parabolic path and all the other
points take different paths. ----- CENTRE OF MASS

6. The center of mass of a body is defined as a point where the
entire mass of the body appears to be concentrated.
.. . ..

7. Let m1, m2, m3 . . . mn be point masses of n particles.
Let, x1, x2, x3 . . . xn be the position of the respective particles
along X-coordinate.
Centre of mass for distributed point
masses

8. The center of mass for y and z coordinates

9. Let us consider two point masses m1 and m2, which are at
positions x1 and x2 respectively on the X-axis.
Centre of mass of two point
masses

10. Centre of mass of two point
masses

11. Centre of mass of two point
masses

13. Centre of mass of two point
masses

14. Centre of mass of two point
masses

15. Example Problem

24. Evaluation
1. Define center of mass.
2. Is centre of mass a point or mass?
3. Find out the center of mass for the given geometrical
structures. a) Equilateral triangle b) Cylinder c) Square