Science Ch. 5 Lesson 4By Grace O’Doherty

Gravity: A Force of Attraction

•a force of attraction between two objects that is due to their masses is called gravity

All Matter is Affected by Gravity

• all matter has mass and gravity is a result of mass (therefore, all matter experiences gravity)

• this gravitational force “pulls” objects towards one another

• you don’t see this force of attraction because the mass of most objects is too small

Earth’s Gravitational Force is Large

•compared to most objects around you, the Earth has an enormous mass which means it also has an immense gravitational pull

•Earth’s gravitational force pulls everything toward the center of the Earth

The Law of Universal Gravitation

• a British scientist named Newton whose work on forces and light was very important in the vast development of science

• it is believed that Newton made a huge connection when he saw an apple fall from a tree

• he concluded that there had to be an unbalanced force on the apple in order to make it fall and that that certain force was called gravity

• Newton generalized his observations on gravity in a law now known as the law of universal gravitation

• this law describes the relationships between gravitational force, mass, and distance

The Law of Universal Gravitation

•this law firmly states that all objects of the universe attract each other through gravitational force

•the law of universal gravitation can also be expressed mathematically:

• F = G X (M1 X M2) Over R(squared) where G = 6.673 X 10 (to the negative eleventh) and N X M(squared) over kg(squared)

Part 1: Gravitational Force Increases as Mass Increases

•the moon has less mass than Earth, therefore, the moon’s gravitational force is less than that of the Earth

Part 2: Gravitational Force Decreases as Distance Increases

•the gravitational pull between you and the Earth is large while you have a weak gravitational pull towards the sun

•the reason for this is because of distance (you are close to Earth but far away from the sun)

Weight Is a Measure of Gravitational Force

•the measure of the gravitational force exerted on an object is called weight

•weight is expressed in newtons (N)

Weight and Mass Are Different

•weight changes when gravitational force changes while the value of mass never changes

•gravitational force is about the same everywhere on Earth, so the weight of any object is about the same