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Coulomb’s Law. An inverse square law. Strength. Which force is stronger, GRAVITATIONAL ELECTROSTATICS?. (Examples static cling in dryer and d ry ink in paper copiers). Which force is stronger?. View the following videos: Cavendish torsion experiment Floating Bill Fun Fly Stick
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Coulomb’s Law An inverse square law.
Strength • Which force is stronger, GRAVITATIONAL ELECTROSTATICS? (Examples static cling in dryer and dry ink in paper copiers)
Which force is stronger? • View the following videos: • Cavendish torsion experiment • Floating Bill • Fun Fly Stick • Fun with Static Electricity: Jedi Board Trick • Electromagnetic Force by Brian Greene • The Office ?
Law of Universal Gravitation • A review from last semester… Where G = 6.67 X 10 -11 N m2 / kg 2
Using this… • Find the force of the moon around the Earth • MEARTH = 6 X 10 24 kg , mMoon = 7.3 X 10 22 kg and the distance between them is 3.9 X 108m Plug in to Final answer is 1.92 X 10 20 N
Origin of Law • Charles Coulomb (1761) developed a similar apparatus to the torsional balance developed by Cavendish
The law • Coulomb’s Law is • Where Q is charge measured in Coulomb’s (large unit--- 3 to 5 coulombs in lightning) • K is the dielectric constant which is variable for different materials. 9 X 10 9 in air (most common)
Example • A positive charge of 1.2 X 10 -6Coulomb (also known as a micro-coulomb) and a 1.6 X 10-6 C negative charge separated by a distance of 20 cm (0.20 m). • (Remember k=9 X 10 9 N m2/ C2)
Inverse Square Law • What happens to the force when you double a distance between charges? • What happens to the force when you half the distance between charges?