Newton's discovery of the universal nature of the force of gravity was remarkable. To take the familiar force that makes an apple fall to Earth and be able to recognize it as the same force that keeps the planets on their quiet and predictable paths represents one of the major achievements of human intellectual endeavor. This ability to see beyond the obvious and familiar is the mark of a true visionary. Sir Issac Newton's pioneering work epitomizes this quality.

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   is an equation

The internationally recognized Systeme International (Sl) is a system of measurement units. The Sl units for length (meter) and mass (kg) are taken from the metric system. Many dictionaries and mathematics and science textbooks provide conversion tables between the metric system and other systems of measurement. Units conversion is very important in all areas of life. For example in currency exchange, airplane navigation, and scientific research.

• What common objects have a mass of about 1 kg?
• What are the dimensions of this sheet of paper in cm and inches?
• How many liters are there in a gallon?

Scientific notation makes it easier to read, write, and manipulate numbers with many digits. This is especially useful for making quick estimates and for indicating the number of significant figures.

Which is bigger, 6 x 10 ^-3 or 8 x 10 ^-4? 6 x 10 ³ or 8 x 10⁴ ? How much bigger?

• How does a scale work ?
• What does a scale measure?
• How many different kinds of scales can you list?
• Do they need gravity for them to work?
• Would you get different results on the Moon or Mars?
• How can you measure the mass of an object in microgravity?