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Gravity S Agenda: Tuesday, 9/08/09 CW:Go over notebook checks Review for quiz over motion, force, velocity, and friction. Begin gravity notes HW:Review for tomorrow’s quiz. Warm Up, Tuesday, 9/8/09 complete on NB page 20. S Have you ever seen a video of astronauts on the moon? They bounce around like beach balls even though they wear big, bulky spacesuits. Why is leaping on the moon easier than leaping on Earth? S Gravity is a force of attraction between objects that is due to their masses. Answer the following question on NB p. 20 S Since gravity is a force, how can gravity change the motion of an object? S The force of gravity can change the motion of an object by changing its speed, direction, or both. S All matter has mass. Gravity is a result of mass. Therefore, all matter is affected by gravity. S Since all objects are being pulled toward you and toward each other because of gravity, why don’t you notice objects moving toward each other? S The mass of most objects is too small to cause a force large enough to move objects toward each other. Agenda: Friday, 9/11/09 CW:Data Analysis and Graphing of Speed/Velocity Lab data Continue gravity notes HW:Complete graphing speed worksheet Force Mass Motion Test will be Friday, 9/25/09 S Since Earth’s mass is so large, Earth’s gravitational force is very large. Answer the question below on notebook page 20. S Why must you exert a force to pick up an object? Newton and the Study of Gravity S Sir Isaac Newton realized that what causes objects to fall toward the Earth and the planets moving in the sky were part of the same problem. S Legend is the Newton made the connection between the two problems while watching a falling apple. S Newton summarized his ideas about gravity in a law now known as the Law of Universal Gravitation. S The law describes the relationships between gravitational force, mass, and distance. It is called universal because it applies to all objects in the universe. The Law of Universal Gravitation S All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between the objects. The gravitational force between objects increases as the masses of the objects increase. Sketch or explain the relationship between mass and gravity on NB page 20. S Mass is a measure of the amount of matter in an object. S The gravitational force between objects decreases as the distance between the objects increases. S Sketch or explain the relationship between distance and gravity on NB page 20. S Venus and Earth have approximately the same mass. But because Venus is closer to the sun, the gravitational force between Venus and the sun is greater than the gravitational force between Earth and the sun. S Gravity is a force of attraction between objects. S Weight is a measure of the gravitational force on an object. Its value can change with the location of the object in the universe. S Weight changes when gravitational force changes. S Mass is the amount of matter in an object. S Gravitational force is the same everywhere on Earth so the weight of any object is about the same everywhere on Earth. S You know that the SI unit of force is a newton (N). Gravity is a force, and weight is a measure of gravity. So weight is measured in newtons. S The SI unit of mass is the kilogram (kg). S When you use a scale, you are measuring the gravitational force between an object and the Earth. So you are measuring weight, which should be given in newtons. However, most bathroom scales have units of pounds or kilograms instead of newtons. Thus, people sometimes mistakenly think that the kilogram is a unit of weight. Don’t be fooled! The correct unit for measuring weight is the newton.