Space Systems: What is gravity? By Encyclopaedia Britannica, adapted by Newsela staff on 04.19.17 Word Count 453 Level MAX
The Milky Way galaxy is visible over the Very Large Telescope in Chile. Gravity is a pulling force that works across space. It shapes our planet, our galaxy, and the entire universe. Photo by: European Southern Observatory.
All objects attract other objects because of a force called gravity. Gravity is a pulling force that works across space. That is, objects do not have to touch each other for the force of gravity to affect them. For example, the sun, which is millions of miles from Earth, pulls on Earth and the other planets and objects in the solar system.
Gravity On Earth
On Earth gravity pulls objects toward the center of Earth. This is what makes objects fall. It is also what gives an object weight. Weight is a measurement of the force of gravity between an object and the surface it stands on. If a person stands on a scale, gravity pulls the person against the scale. The scale shows the strength of this force, or the person’s weight.
This article is available at 5 reading levels at https://newsela.com. 1 Gravity In Space
In the solar system the planets all orbit, or travel around, the sun in a constant path. They would move in a straight line, but the force of gravity pulls them toward the sun. Simultaneously, the speed of the planets in their orbits keeps them from falling into the sun.
This article is available at 5 reading levels at https://newsela.com. 2 Spacecraft and satellites travel around Earth in a similar way. So does Earth's moon. Earth’s gravity maintains these objects in their orbit, and their speed keeps them from falling back to Earth.
When astronauts are inside a spacecraft in orbit, they experience weightlessness. The astronauts are suspended freely because they are traveling around Earth at the same speed as the spacecraft. But even though Earth’s gravity does not pull them toward the floor—as it does on Earth—they have not escaped it. Earth’s gravity keeps the astronauts in orbit, just as it does the spacecraft.
Newton's Law Of Gravity
This article is available at 5 reading levels at https://newsela.com. 3 Isaac Newton, an English scientist, discovered a law, or truth, about gravity in the late 1600s. Newton said that the force of gravity between objects depends on their mass, or the amount of material they contain. The greater the mass of an object, the greater is its force of gravity. For example, the sun, which has a mammoth mass, has a greater force of gravity than Earth, which has a much smaller mass. Even a speck of dust has a force of gravity. But its gravity is extremely small.
The force of gravity also varies based on the distance between two objects. The smaller the distance, the more powerful the force of gravity between them.
This article is available at 5 reading levels at https://newsela.com. 4 Quiz
1 Which section from the article BEST explains HOW to measure the strength of the force between an object and the surface it stands upon?
(A) Introduction [paragraph 1]
(B) "Gravity On Earth"
(C) "Gravity In Space"
(D) "Newton's Law Of Gravity"
2 Which piece of evidence from the article explains WHY the sun has a larger force of gravity than the Earth?
(A) Isaac Newton, an English scientist, discovered a law, or truth, about gravity in the late 1600s.
(B) The greater the mass of an object, the greater is its force of gravity.
(C) Even a speck of dust has a force of gravity.
(D) The smaller the distance, the greater is the force of gravity between them.
3 Read the paragraph from the section "Gravity In Space."
When astronauts are inside a spacecraft in orbit, they experience weightlessness. The astronauts float freely because they are traveling around Earth at the same speed as the spacecraft. But even though Earth’s gravity does not pull them toward the floor—as it does on Earth —they have not escaped it. Earth’s gravity keeps the astronauts in orbit, just as it does the spacecraft.
How does the paragraph help develop the idea that gravity works across space?
(A) It describes the path a spacecraft takes when traveling with weightless astronauts as opposed to heavy astronauts.
(B) It explains why astronauts feel weightlessness when traveling through space but not when on the spacecraft.
(C) It shows how gravity still affects astronauts on a spacecraft even though they are experiencing weightlessness.
(D) It provides an example of how gravity from Earth pulls a person to the floor of the spacecraft while in orbit.
This article is available at 5 reading levels at https://newsela.com. 5 4 How does the following sentence contribute to the development of the main idea in the article?
The force of gravity also depends on the distance between two objects.
(A) It restates the idea that all objects are attracted to one another because of gravity.
(B) It explains why astronauts float in a spacecraft but not while still on Earth.
(C) It identifies another factor that affects the amount of gravity between objects.
(D) It illustrates why bigger objects that are far apart have the largest force of gravity.
This article is available at 5 reading levels at https://newsela.com. 6 Answer Key
1 Which section from the article BEST explains HOW to measure the strength of the force between an object and the surface it stands upon?
(A) Introduction [paragraph 1]
(B) "Gravity On Earth"
(C) "Gravity In Space"
(D) "Newton's Law Of Gravity"
2 Which piece of evidence from the article explains WHY the sun has a larger force of gravity than the Earth?
(A) Isaac Newton, an English scientist, discovered a law, or truth, about gravity in the late 1600s.
(B) The greater the mass of an object, the greater is its force of gravity.
(C) Even a speck of dust has a force of gravity.
(D) The smaller the distance, the greater is the force of gravity between them.
3 Read the paragraph from the section "Gravity In Space."
When astronauts are inside a spacecraft in orbit, they experience weightlessness. The astronauts float freely because they are traveling around Earth at the same speed as the spacecraft. But even though Earth’s gravity does not pull them toward the floor—as it does on Earth —they have not escaped it. Earth’s gravity keeps the astronauts in orbit, just as it does the spacecraft.
How does the paragraph help develop the idea that gravity works across space?
(A) It describes the path a spacecraft takes when traveling with weightless astronauts as opposed to heavy astronauts.
(B) It explains why astronauts feel weightlessness when traveling through space but not when on the spacecraft.
(C) It shows how gravity still affects astronauts on a spacecraft even though they are experiencing weightlessness.
(D) It provides an example of how gravity from Earth pulls a person to the floor of the spacecraft while in orbit.
This article is available at 5 reading levels at https://newsela.com. 7 4 How does the following sentence contribute to the development of the main idea in the article?
The force of gravity also depends on the distance between two objects.
(A) It restates the idea that all objects are attracted to one another because of gravity.
(B) It explains why astronauts float in a spacecraft but not while still on Earth.
(C) It identifies another factor that affects the amount of gravity between objects.
(D) It illustrates why bigger objects that are far apart have the largest force of gravity.
This article is available at 5 reading levels at https://newsela.com. 8