Center of Mass and Center of Gravity

The center of mass is a position defined relative to an object or system of objects. It is the average position of all the parts of the system, weighted according to their masses.

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This point is where all the weight of the object may be considered to act.

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1. Hang up the object.

2. Suspend a plumb line from the same place.​

3. Mark the position of the thread.

4. The centre of mass is along the line of thread.

5. Repeat the above steps with object suspended from different places.

6. The centre of mass is where these lines cross.

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A rod with a mass of 4 kg and a length of 9 m. If the rod rotates at its edge with an angular speed of 20 rad/s, calculate its rotational energy.

 Kinetic Energy of Rolling Motion is Translational KE​+ Rotational KE

​A cylinder of mass 4 kg and radius 2 m rolls without slipping down a ramp at speed of 2 m/s. Calculate its total kinetic energy at this speed!