Okeey Essay

7851 words - 31 pages

ENERGI DAN PERUBAHANNYA (S D )ENERGI DAN PERUBAHANNYA (S D )BAB IIENERGI DAN PERUBAHANNYAPengertian EnergiApakah yang dimaksud dengan energi? Energi dibutuhkan diantaranya untuk menggerakkan mobil, untuk memanaskan dan mendinginkan ruangan, dan menjalankan komputer. Energi matahari diperlukan antara lain untuk pertumbuhan tanaman dan proses siklus air. Energi yang terdapat dalam makanan menyediakan energi bagi manusia, baik berjalan, olah raga, bernyanyi, bekerja, belajar, berpikir, saat melamun, bahkan saat tidurpun memerlukan energi. Manusia membutuhkan berjuta-juta kalori setiap harinya untuk melakukan kegiatan dalam kehidupan sehari-hari. Oleh karena itu, disarankan setiap pagi sebelum beraktivitas kita harus makan dahulu. Dengan demikian, tubuh kita memiliki cukup energi untuk melakukan segala kegiatan dan kesehatan tubuh akan selalu terjaga.Seseorang yang terus melakukan kerja, misalnya memindahkan barang lama-kelamaan akan merasa lelah dan akhirnya orang tersebut tidak mampu lagi memindahkan barang. Hal tersebut disebabkan pada saat orang memindahkan setiap barang akan mengeluarkan energi.

Gambar 1. Seseorang yang memindahkan barang terus menerus lama-kelamaan akan merasa lelah karena kehabisan energiDari contoh di atas terlihat bahwa energi dan kerja merupakan dua hal yang tidak dapat dipisahkan. Artinya, jika pada suatu benda diberikan energi, pada benda tersebut timbul kerja atau usaha.Sebagai gambaran untuk memahami lebih jauh pengertian energi dan bagaimana kaitannya dengan kerja atau usaha, dapat kita rasakan pada saat melaksanakan puasa. Pada saat berpuasa badan terasa lemas kurang bertenaga, sedangkan jika tidak berpuasa badan terasa segar.Pada saat berpuasa, energi makanan yang dikonsumsi lebih sedikit dibandingkan dengan energi yang dikonsumsi pada saat tidak berpuasa. Badan menjadi segar kembali beberapa saat setelah berbuka puasa. Mengapa hal itu terjadi? Sumber energi yang dimiliki manusia berasal dari makanan dan minuman. Badan menjadi segar kembali, karena kekurangan energi selama berpuasa telah diganti kembali setelah mengkonsumsi makanan dan minuman. Tentunya, makanan dan minuman tidak dapat langsung berubah menjadi energi tetapi harus mengalami suatu proses atau diolah dulu oleh sistem pencernaan tubuh. Setelah mengalami proses pencernaan di dalam tubuh, zat-zat makanan berubah menjadi energi. Selanjutnya, energi yang dihasilkan dapat digunakan sehingga badan dapat melakukan aktivitas kembali.Energi dan UsahaManusia, hewan, tumbuhan, dan mesin pada saat melakukan aktivitasnya selalu memerlukan energi. Energi yang digunakan manusia, hewan, dan tumbuhan berasal dari berbagai makanan dan minuman yang dikonsumsinya. Energi yang digunakan mesin mobil berasal dari bahan bakar berupa bensin, solar, atau dapat juga berupa bahan bakar bentuk lainnya. Kemudian energi yang dimiliki mesin digunakan untuk melakukan usaha, misalkan mesin mobil digunakan untuk menggerakkan mesin - mesin mobil sehingga mobil dapat bergerak. Peristiwa...

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