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 attraction that acts between any two objects that have a mass. So why isn’t your notebook attracted to you now? Because, one or both of the objects must be very massive (like a planet, star, or moon). Scientist’s know the acceleration of gravity is… = 9.8m/s 2

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. In other words, the apple is more attracted to the Earth than the apple tree because the Earth is more massive than the tree= more gravitational force pulling.

Differences Between Gravity and Friction The force of gravity acts even when objects are not touching. Friction must ALWAYS be touching! The force of friction can never make an object speed up! Friction always points in the opposite direction of motion, 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. The greater the mass of an object, the more gravity it has pulling on it and other objects.

More about Gravity Also, as the distance between two objects increases, the less gravity pulling on the two objects.

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 (6.67x N x m 2 /kg 2 )and makes the units right! Units for g = Newton’s (N)

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!

QUESTION???? Which has more gravitational force…the earth and you or you and your neighbor? Why? (Use the formula… F G = G x m 1 x m 2 d 2 You (60.4 kg) and your neighbor (70.5 kg) and d=1.5 m You (60.4 kg) and the earth (5.9742×10 24 kg) But what is your weight? They’re the same! … but how?!?!?! 1.26 x N 591 N

The Acceleration Due to Gravity: We can calculate it! At ground level: What’s this? 9.80 m/s 2 = g But we can calculate “g” anywhere, caused by any object with mass!

The Acceleration Due to Gravity: How does g change with altitude? Altitude (m) Distance From the Center of g due to the Earth's Gravity What has This Altitude? the Earth (m)(m/s 2 ) Lying on the Earth Height of a person On a small roof Highest point in Delaware Empire State Building Height of Mount Everest Airplane International Space Station Twice the Earth's Radius The Moon 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!

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

1.Which astronaut has the most gravity pulling on them? 2.Who’s weight will change? 3.Who’s mass will change? 4.Which two planets have the most gravity between then? 5.The least amount? A C B A B and C No one A and C (closest) C and B (farthest) 6. Which planet has the least amount of gravity? B (has smallest mass)

RFA 19 #4 D (6.673x Nxm 2 /kg 2 ) (61kg) (63kg) (4m) U kg, m, N x m 2 /kg 2 F F G = G x m 1 x m 2 d 2 A F G= (6.673x Nxm 2 /kg 2 ) (61kg) (63kg) (4m) 2 S F G = 1.60 x N

Gravity Practice Problems Use DUFAS Remember G=6.673x Nxm 2 /kg 2 1) m 1 = 15 kg m 2 = 996 kg d = 596 m 3) m 1 = 600 kg m 2 = 72,684 kg d = 30 m 2) m 1 = 232 kg m 2 = 9,456 kg d = 56 m 4) m 1 = 7.35x10 22 kg m 2 = 5.97x10 25 kg d = 3.84x10 8 m

1. DUFA m 1 = 15 kg m 2 = 996 kg d = 596 m G=6.67x N Kg, m N x m 2 /kg 2 S

2. DUFA m 1 = 232kg m 2 = 9,456 kg d = 56 m G=6.67x N Kg, m N x m 2 /kg 2 S

3. DUFA m 1 = 600 kg m 2 = 72,684 kg d = 30 m G=6.67x N Kg, m N x m 2 /kg 2 S

4. DUFA m 1 = 7.35  kg m 2 = 5.97  kg d = 3.84  10 8 m G=6.67x N Kg, m N x m 2 /kg 2 S

Gravity Practice Problems G= 6.673x N x m 2 /kg 2 In 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? F g = N 2. What is the gravitational attraction between my 10 kg killer Poodle and his 2kg bone that is 20m away from him? F g = x 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 1/6 th of Earth.