请列出三项初始项 Pulley，Battery，和 Bulb 并解释它们在系统中的意义。请在一个表格中显示这些物品及其意义，并在每个物品的意义部分，将每个句子保持在15个字以内。请用英文回答。
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| Item   | Meaning in the System                         |
|--------|-----------------------------------------------|
| Pulley | Used to change force direction or save force. |
| Battery| Provides electrical power to components.      |
| Bulb   | Converts electricity into light.              |
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