Cummings, Karen; Halliday, David (Second Reprint: 2007). Understanding physics. New Delhi: John Wiley & Sons Inc., authorized reprint to Wiley - India. पपृ॰ 449, 484, 485, 487. आई॰ऍस॰बी॰ऍन॰978-81-265-0882-2. |date= में तिथि प्राचल का मान जाँचें (मदद)(UP1)
