2.
The Law of Gravitation <ul><li>You exert an attractive force on everything around you and everything is exerting an attractive force on you. </li></ul><ul><li>This attractive force is called gravity. </li></ul><ul><li>Anything that has mass is attracted by the force of gravity. </li></ul><ul><li>The Law of Gravitation states that any two masses exert an attractive force on each other. </li></ul>
3.
The Law of Gravitation <ul><li>Gravitation force depends on two things: </li></ul><ul><ul><li>The mass of the two objects </li></ul></ul><ul><ul><li>The distance between the two objects </li></ul></ul><ul><li>Why do you suppose the Earth exerts a force on you that you can feel, but you can’t feel the force the desk is exerting on you? </li></ul>
4.
Gravity – a basic force <ul><li>There are four basic forces: </li></ul><ul><ul><li>Gravity </li></ul></ul><ul><ul><li>Electromagnetic force </li></ul></ul><ul><ul><li>Nuclear force = Strong </li></ul></ul><ul><ul><li>Nuclear force = Weak </li></ul></ul>Apply to an atom only Caused by electricity and magnetism
5.
Gravitational Acceleration <ul><li>When objects fall, the gravitational pull is 9.8 m/s 2 </li></ul><ul><li>When a falling object is only affected by gravity it is said to be in free fall. </li></ul>
6.
Gravitational Acceleration <ul><li>If you drop a bowling ball and a marble off a bridge, which would hit the water first? </li></ul><ul><li>Things to consider… </li></ul>
7.
Gravitational Acceleration <ul><ul><li>Force of gravity is greater on the bowling ball because of its larger mass. </li></ul></ul><ul><ul><li>The larger mass means it has a larger inertia so more force is needed to change its velocity. </li></ul></ul><ul><ul><li>Gravitational force on the marble is smaller because it has a smaller mass </li></ul></ul><ul><ul><li>The inertia on the marble is less and less force is needed to change the velocity. </li></ul></ul><ul><ul><li>Therefore, all objects fall with the same acceleration! </li></ul></ul>
8.
Weight <ul><li>Even if you are standing still and you have zero acceleration, the force of gravity is still present. </li></ul><ul><li>Weight is equal to the support force, which under normal circumstances is also equal to the force exerted on an object by gravity. </li></ul><ul><li>Capital W stands for weight. </li></ul><ul><li>F g = mass x (acceleration due to gravity) </li></ul>
9.
Weight <ul><li>Because the gravitational force is the same as the weight and the acceleration due to gravity, the equation can also be written as: </li></ul><ul><li>W = (m)(9.8 m/s 2 ) </li></ul><ul><li>… if the object is being supported! </li></ul>
10.
Weight & Mass <ul><li>Weight and mass are not the same thing. </li></ul><ul><li>Weight is a force </li></ul><ul><li>Mass is a measure of the amount of matter an object contains. </li></ul><ul><li>The greater the weight, the greater the attraction between the object and Earth. </li></ul>
11.
Weightlessness <ul><li>To be nearly weightless, you would have to be far from the Earth. </li></ul><ul><li>Astronauts experience this feeling when they are in space. </li></ul><ul><li>Why does the space station spin? </li></ul>
12.
Gravity Factors <ul><li>The acceleration due to gravity is directly proportional to the mass of the objects and inversely related to the distance squared. </li></ul>
13.
Inverse Square Law <ul><li>When a quantity varies as the inverse square of its distance from its source. </li></ul>
14.
Law of Universal Gravitation <ul><li>Every object attracts every other object with a force that for any two objects is directly proportional to the mass of each object. </li></ul>
15.
Universal Gravitation <ul><li>To find the F g between any two objects in the universe. </li></ul><ul><li>G is the gravitational constant of proportionality </li></ul><ul><li>G = 6.67 x 10-11 N m 2 /kg 2 </li></ul><ul><li>F = G m 1 m 2 /r 2 </li></ul>
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