Activity 4: Gravity & Astronomy
This activity discusses the concept of gravity, how it works, and its all important role in the formation and maintenance of the universe.
To teach the fundamentals of astronomy as it relates to gravity.
Students will be able to:
Set up: 10 min.
Anything that takes up space is said to have mass. All forms of matter, including plants, animals, rocks, liquids, and gases, have mass. A mountain has much more mass than a mouse but, mass is different than size because a marble has more mass than a inflated balloon. Even forms of energy like light waves have a tiny amount of mass. For more discussion on mass and matter refer to Do we need to Diet on Mars? activity.
Mass and energy are closely related. Matter stores energy. When matter is put under stress it releases energy. For example, when wood is burned it releases energy in the form of heat and light. Albert Einstein's formula:
which suggests that not only can a small amount of matter create a huge amount of energy, but also that a huge amount of energy can create a small amount of matter.
All matter in the universe is expanding outward in all directions at once, as if long ago everything exploded from a single point. Astronomers explain this phenomena with the Big Bang Theory. The Big Bang Theory suggests that everything began 13.7 billion years ago in a colossal explosion. Initially the universe only existed as energy, but as it began to cool and expand itself across the void of space this huge amount of energy quickly created the simplest forms of matter: hydrogen and helium gases. With matter came the mysterious force of gravity.
All matter has gravity, and gravity affects all matter and even some forms of energy, like light. Gravity is the mutual pull or attraction of objects towards each other. The English scientist Isaac Newton measured gravity using the following formula:
Gravitational Attraction =
More massive objects have more gravity than smaller objects, but the most important variable that determines the strength of gravity is distance. As objects move further apart, their gravitational attraction to one another dramatically decreases.
The escape velocity for Earth is about 25,000 mph (40,320 km per hour), therefore any object traveling that speed or faster has the ability to leave the gravitational pull of Earth. Objects that move very fast but do not approach the speed of escape velocity are said to be in orbit. Instead of flying off into space they resist the force of gravity by revolving around the source of gravitational pull. This is why our Moon never crashes into Earth. Moon's velocity and Earth's gravitational pull balance each other out so that Moon neither escapes nor collides with Earth. However this balance is not perfect, our Moon is slowly drifting farther and farther, slowly increasing the size of its orbit.
Gravity is thought to be the main force that shapes and organizes all matter in the universe. Because of gravity's consistent and predictable influence the largest objects in the universe are similar to the smallest objects. For example, galaxies form in a similar manner as our solar system did.
After the Big Bang, gravity began to pull gases like hydrogen and helium closer and closer together, forming billions of enormous clouds called proto-galaxies. As each proto-galaxy continued to condense, some of the radial motion from the Big Bang was converted into angular momentum causing the cloud to spin. The more the cloud condensed the faster it rotated, just as a figure skater spins faster when she pulls her arms and legs in towards her. Within the proto-galaxy billions of much more dense clouds called nebulas began to form and also spin. Most of the matter in these nebulas eventually concentrated into individual zones. At these centers, the hydrogen gases were under so much gravitational pressure that they condensed and ignited to form stars where hydrogen is first converted into helium gas, and later into other heavier elements. This conversion process known as nuclear fusion creates phenomenal amounts of energy, which is why stars burn so hot and brightly.
These first-generation stars continued burning for millions and billions of years until they ran out of hydrogen. Without hydrogen they began to fuse helium into carbon, oxygen, and iron causing the star to swell in size. The largest of these stars, called supergiants, died in catastrophic and blinding explosions called supernovas. Supernovas are so bright that they can sometimes be seen on Earth in the day time! During these powerful explosions all the more complex and heavy forms of matter including silver, gold, lead, uranium, etc. are formed and blasted into deep space forming new smaller nebula.
These nebulas will again contract under the power of gravity and began to spin, eventually spawning second-generation stars and also something new: planets. It is thought that planet formation is only possible in nebulas with heavy minerals. Because heavy minerals have more concentrated mass and therefore more gravity, that makes it possible for multiple gravitational centers to form in addition to the proto-star at the center. The local gravitational pull of these proto-planets were stronger than the larger but much more distance influence of the central star. The more matter these early planets absorbed, the stronger their gravitational attraction became. Increasing mass also caused the planets to accelerate along their orbital paths, thus better resisting the pull of the growing star.
As these maturing planets raced through the nebula, the larger planets captured smaller ones, which became their moons. For about a billion years the young planets endured countless impacts from smaller asteroids and comets. At last, the free floating material that once made the nebula was either all absorbed into the star and planets, or blasted away into deep space by the diverse mix of energy, called solar wind, emitted by the young star. It is in this manner that our solar system formed.
Therefore, gravity is more than just what makes things fall on Earth. Gravity is the great glue that shapes and maintains the universe.
Note: Recent discoveries involving distant supernovas suggest, as Albert Einstein once speculated, that an anti-gravitational force also exists. It had always been assumed that gravity slows down the universe's expansion, eventually reversing the motion so that the universe might end in a Big Crunch. However, the analysis of light from distant supernovas suggests that the universe is NOT slowing down, but continuing to accelerate! Initial speculation is that a property of nothingness is repulsion. Perhaps the more nothing there is between objects, the more powerful this anti-gravity force is? If this is true, the universe is getting bigger at a faster and faster rate. All of the galaxies are growing farther apart from each other.
As the game progresses, ask the students to speculate which students are most and least likely to be absorbed by larger objects. Ask them how many turns they think it will take before all students are joined as one object. As the game is played periodically stop and encourage the students to discuss what they see as analogous to the formation of a solar system. Are there planets? with moons? How many stars? Etc.
The Solar System!
The Solar System with Moons!
Using Real Math!
Formula 1 (simplified version):
Formula 2 (Newton's actual formula):
Encourage the students to do further research into the planets. Assign them research papers and or presentation on individual planets.
Included National Parks and other sites:
Utah Science Core:
3rd Grade Standard 3 Objective 1,2