Center of Mass and Center of Gravity

Center Mass, Rotational Energy, and Rolling Motion

by Susanto,S.Si

​Center Mass

Poll

In your opion which location of center Mass?

• A

• B

• No idea

​Center Mass

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.

​Center mass experiment

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Multiple Choice

Based on the video the video, where is the center of mass of the object?

• A

• B

• C

• D

​Center mass of irregular object experiment

Open Ended

Arrange this following stages into the correct stage of experiment to find center of gravity!

A. Suspend a plumb line from the same place.

B. Hang up the object.

C. Mark the position of the thread.

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

E The centre of mass is where these lines cross.

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

​Experiment Stages to Find Center Mass

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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.

Rotational Energy

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​Kinetic Energy (KE)

​Example

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.

​Rolling Motion

 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!