Two kinds of forces

• Contact forces – you push me

• Field forces – parachutist gets pulled down by earth

I dream of Jeannie

• Nugget of gold– How does earth know?

• Magnet by other magnet– How does magnet know?

• Charged particle by other– How does charge know?

Big mass, big charge

• Earth big force on a big mass – elephant

• Small force on small mass – ant

• Same with charges

Gravitation field

• Earth alone has a gravitational field, just ask any dinosaur about the meteor that got captured in it 60,000,000 years ago

• Earth waits in shadows for a mass to come by

• Charge has a force field too

• Waits for another charge to come by

• NO CONTACT REQUIRED!

Mapping

• You can map gravitational fields 22,000 miles away:– Earth pulls left– Moon pulls right– Sun right

• Add them together

• Repeat at several locations, a map!

• Electric field mapping is same