**What is Gravity?** • Write down anything you may know about gravity. • Any examples of gravity • Where you may find it or not find it!

**What is Gravity?** Gravity is an attractionthat acts between any two objects that have a mass. So why isn’t your notebook attracted to you now? 1. Gravity is only significant if, one or both of the objects are very massive (like a planet, star, or moon). Scientist’s know the acceleration of gravity is… = 9.8m/s2

**Let’s review… ** What’s matter? Anything that has a mass and takes up space So…What’s mass? How much matter is in an object. Then what’s Weight? How much gravity is pulling on an object.

**An example of Gravity** Every object applies a gravitational force to every other object. So why does an apple fall from a tree? The apple falls because it is more attracted (gravitational force) to the Earth than it is to the tree.

**Differences Between Gravity and Friction** 1. The force of gravity acts even when objects are not touching. 2. Friction must ALWAYS be touching! 3. The force of friction can never make an object speed up! 4. Friction always points in the opposite direction of motion, 5. But gravity sometimes points in the direction of motion.

**Mass and Distance** Mass and Distance affect Gravitational Force. The force of gravity depends on the masses of two objects and the distance between them. 2. The greater the mass of an object, the more gravity it has pulling on it and other objects.

**More about Gravity** 3. The further away the object is from the center of the Earth, the less gravity it will have pulling on it.

**The Acceleration Due to Gravity:How does g change with** altitude? Does the gravitational pull near the surface change much? No! The gravitational pull remains nearly constant! You would have to be hundred’s of miles away for gravity to really affect you!

**Summarizing Gravity** • Gravity is only significant if, one or both of the objects are very massive (like a planet, star, or moon). • As object get larger, the more gravity is pulling on them. • As objects get further away from each other, the less gravity is pulling on them.

**Earth vs. Terrestrial Planets (Rocks)**

**Earth vs. Jovial Planets (Gas)**

**Sun vs. The Planets**

**Sun vs. Other Stars**

**Other Stars**

**More about Gravity** Gravity is the reason why weight and mass are two different measurements!!! Mass is related to the amount of matter in an object. Weight = the force of gravity pulling on any object. (w=mg) So…which one would change if you were on the moon? Why? Weight, because the force of gravity pulling on an object on the moon is only 1/6 of that on the Earth!

***Gravity Drop** If I drop a golf ball and a plastic fuzzy ball at the same time, which one hits the table first? The both hit at the same time! BUT, what if I drop a volley ball and a bowling ball at the same time? Which one will hit the ground first? Let’s try it! So what happened?

** Gravitational Force Formula** My name is Sir Isaac Newton and I figured this out! d is the distance between the centers of the two objects. G is called the “gravitation constant” it equals (6.67x10-11 N x m2/kg2)and makes the units right! Units for g = Newton’s (N)

**The Acceleration Due to Gravity:** So what is g for the moon, on the surface of the moon?

**QUESTION????** Which has more gravitational force…the earth and you or you and your neighbor? Why? (Use the formula… FG = G x m1 x m2 d2 You (60.4 kg) and your neighbor (70.5 kg) and d=1.5 m You (60.4 kg) and the earth (5.9742×1024 kg) But what is your weight? 1.26 x 10 -7 N 591 N They’re the same! … but how?!?!?! 591 N

**The Acceleration Due to Gravity:** We can calculate it! At ground level: What’s this? 9.80 m/s2 = g But we can calculate “g” anywhere, caused by any object with mass!

**RFA 18 #4** D (6.673x10-11Nxm2/kg2) (61kg) (63kg) (4m) U kg, m, N x m2/kg2 F FG = G x m1 x m2 d2 A FG= (6.673x10-11Nxm2/kg2) (61kg) (63kg) (4m)2 S FG = 1.60 x 10-8 N

** m1 = 15 kg** m2 = 996 kg d = 596 m 3) m1 = 600 kg m2 = 72,684 kg d = 30 m 2) m1 = 232 kg m2 = 9,456 kg d = 56 m 4) m1 = 7.35x1022 kg m2 = 5.97x1025 kg d = 3.84x108 m Gravity Practice ProblemsUse DUFASRemember G=6.673x10-11Nxm2/kg2

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**Gravity Practice ProblemsG= 6.673x 10-11 N x m2/kg2In DUFAS** 1. What is the gravitational attraction between an object with a mass of 10 kg and another object with a mass of 20 kg if they are separated by 0.01 meters? Fg= 0.0001334 N 2. What is the gravitational attraction between my 10 kg killer Poodle and his 2kg bone that is 20m away from him? Fg= 3.335 x 10-12 N

**Gravity Practice** 1. Explain why a tree’s leaf falls to the earth. 2. Who has more gravity pulling on them…a 350 lb offensive lineman or a 215 lb wide receiver on a football field? And why? 3. Why is there less gravity on the moon than here on Earth?

**Gravity Answers** 1.The leaf falls to the Earth b/c the Earth has a larger mass than the tree so it has a greater gravitational pull on the leaf. 2. The 350 lb lineman b/c he has more mass. More mass= more gravity pulling on that mass. 3. There is less gravity on the moon because you are very far from the center of the Earth so the gravitational pull is only 1/6th of Earth.