This power point is modified from the Universal Gravitation power point found at: http://www3.science.tamu.edu/CMSE/powerpoint/ on 1/5/10

What is gravity?What is gravity?

Galileo

Sir Isaac Newton

Galileo and and Newton gave the name gave the namegravitygravity to the force that exists to the force that exists between the Earth and objects.between the Earth and objects.

Newton Newton showed that the showed that the same force same force exists between exists between allall objects.objects.

He even realized that it is He even realized that it is gravitygravity that that keeps the moon keeps the moon in orbitin orbit!!!!Even today, Even today, no one knowsno one knows for sure for sure

why objects attract each other.why objects attract each other.

In 1666, In 1666, Isaac NewtonIsaac Newton determined that the determined that thesame force same force that kept the planets in motionthat kept the planets in motion

must also exist between must also exist between every objectevery object..

He stated that He stated that every objectevery object in the universe in the universe attracts attracts

every other object in the universe. every other object in the universe. The force of attraction between two objects is The force of attraction between two objects is

directly proportional directly proportional to the to the product of their product of their massesmasses, ,

and and inversely proportionalinversely proportional to the to the square of their square of their separation distanceseparation distance..

So, for example, if you So, for example, if you doubledouble the mass of one of the the mass of one of the objects you will objects you will doubledouble the force of attraction the force of attraction

Or Or If you If you half the mass half the mass of oneof one objectsobjectsYou will You will halfhalf the force of attraction the force of attraction

Also, for example, if you Also, for example, if you increase the distanceincrease the distance between between the objects by the objects by double (2double (222=4)=4) you you decreasedecrease the force of the force of

attraction to attraction to ¼¼ of what it was. of what it was.Or Or

If you If you decreasedecrease the distance ( ¼=½the distance ( ¼=½22)) between the objects between the objects by half you will by half you will increase the attraction by four timesincrease the attraction by four times what what

it was. it was.

In equation form:In equation form:

FFF is the is the force of attractionforce of attraction, measured in , measured in NEWTONSNEWTONS,,between masses mbetween masses m11 and m and m22

G

GG is the is the Universal Gravitation ConstantUniversal Gravitation Constant, equal to , equal to 6.67 x 106.67 x 10-11-11 N m N m22/kg/kg22

m1m2

mm11 and and mm22 are the are the attracting massesattracting masses, measured in, measured inKILOGRAMSKILOGRAMS

r2

rr is the is the distance between their centers of massdistance between their centers of mass, , and is measured in and is measured in METERSMETERS

When two large objects exert gravitational forces on each other, the force on the near side is larger than the force on the far side, because the near side is closer to the other object.

This difference in gravitational force across an object due to its size is called a tidal force.

TIDESTIDES

Gravity of moon

Moon’s pull is greatest here because it is closer. Highest tide

Second high tide (smaller then the other) because this side is pulled the least

Tidal lockingTidal lockingThis is what allows only one side of the moon to face the Earth

It can even keep moons from forming!