sign in sign up
<<
Home , Gravity

Gravity: A of Attraction

Station 5 What is Gravity?

• Gravity is a force of attraction between two objects. • All objects with have gravity. • Gravity acts like a magnet pulling objects together. What Does Gravity Do?

• The has gravity. • Gravity holds everything close to this . • Trees, , animals, buildings, and the air we breathe are all held here by gravity. What Does Gravity Do?

• All objects with mass exert a pulling force on each other. • All of the , the and the of the have gravity. Even our own bodies have gravity! Gravitational We Notice:

• The (1.98892 x 1030 kg) is the most massive object in our and exerts a huge gravitational force. • This is why all the planets stay in around the sun.

Gravitational Forces We Notice:

• The Earth (5.9742 x 1024 kg) is so massive that its gravitational force keeps us from falling off the planet! • Compared with all objects around you, Earth has a huge mass. Therefore, Earth’s gravitational force is very large.

Size of Gravity

• Gravity is affected by the and mass of the objects. • The Earth and the have a stronger pull on each other than the Earth and Jupiter because the Earth and moon are closer to one another. Gravitational force is strong when distance between two objects is small. If the distance between two objects increases, the gravitational force pulling them together decreases rapidly. Gravitational force is small between objects that have small . Gravitational force is large when the mass of one or both objects is large. of Gravity • We don't actually "feel" gravity. We only feel the effects of trying to overcome it by jumping or when we fall. • You must apply forces to overcome the Earth’s gravitational force any you objects or even parts of your body.

Mass and

• Mass is the "stuff" that is made of. • We measure mass in grams. • People often confuse mass with weight. Mass and Weight

• Weight is actually the result of gravity pulling on the object. We measure weight in Newtons. • The closer to the center of the Earth, the more pull, the more you weigh.

Mass and Weight

Your mass stays the same if you could travel from planet to planet, but your weight would vary depending on how the gravity of that planet pulls on you. Moon

• Earth has a stronger pull than the moon because it is larger. • There is more pull on our bodies here on the Earth than experience on the moon. • The Earth's tides are caused by the moon's gravitational pull on the oceans. Tides are the rise and fall of the ocean level as related to the shoreline which occurs over every 12 hours or so. • To a lesser degree the moon also pulls on the rivers, lakes and land. When astronauts go into , they “float” because they are far enough away from the center of the earth that the gravitational force isn’t strong enough to hold them down.

Weight on the moon is 1/6 the weight on Earth

Sir Isaac Sir (1642- 1727) was a scientist who is credited with discovering gravity. You would think that gravity would be a well known concept since all of us have been aware of it since we were little kids dropping our spoons on the floor from our high chair just to make mom come and get it. Sir Isaac Newton

But it wasn't until Newton published his ideas in a book in 1687 that the scientific world had gravity as a defined term. Newton is well known for his Three Laws of which explain how the physical laws direct the motion of objects. The Effects of Gravity on Matter

• Gravity is a force of attraction between objects that is due to their masses. Gravity can change the motion of an object by changing its , direction, or both.

• All matter has mass, and gravity is a result of mass. Therefore, all matter is affected by gravity and all objects experience an attraction toward all other objects.

• The mass of most objects is too small to cause a force large enough to move objects toward each other.