Matter In Motion Gravity: A Force of Attraction

Terms Gravity~ a force of attraction between objects that is due to their masses Weight~ a measure of the gravitational force exerted on an object Mass~ the amount of matter in an object, and the value does not change

All Matter is Affected by Gravity All objects experience an attraction toward all other objects The mass of most objects is too small to cause an attraction large enough to move objects toward each other Earth’s gravitational force is large –Caused by its enormous mass –Need to apply forces large enough to overcome it any time you lift objects –Why things fall to the ground when dropped instead of moving together

The Law of Universal Gravitation The core of an idea –Sir Isaac Newton –Unbalanced force must be acting on moving objects –Unbalanced force acting on moon causing it to move around Earth –Same force: Gravity A law is born –States: All objects in the universe attract each other through gravitational force –Applies to all objects in the universe –Force size depends on mass of objects and how far apart they are

The Law of Universal Gravitation Part 1: Gravitational Force increases as mass increase –Cat and elephant: cat smaller~ smaller mass, easier to pick up –Force between cat and elephant small because the masses are much smaller than Earth’s

The Law of Universal Gravitation Part 2: Gravitational force decreases as distance increases –At this distance~ the gravity between you and the sun is small –Due to the masses of the planets, the sun does have a big effect on them

Weight is the Measure of a Gravitational Force On Earth, a 100 g object weighs approx 1 N Weight and mass are different –Weight changes when gravitational force changes –Because weight and mass are constant on Earth, the terms are often used to mean the same thing…know the difference!

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