All About Gravity
What Is Gravity?
No matter how fast a pitched throws a baseball, it will always hit the ground. Have you ever wondered why? It’s the same reason we fall after jumping and why picking up heavy boxes is so hard. These things happen because of gravity. Science defines gravity as the force that makes a celestial body (like a planet or star) attract objects toward its center. The Earth’s gravity keeps people and animals rooted to the surface of the planet, and the gravity of the sun keeps the Earth in a steady orbit through space!
What Else Does Gravity Do?
Earth has its own force of gravity, but not everything on Earth interacts with gravity in the same way. It’s important to understand how mass works with gravity. Planets and objects with less mass have a weaker gravitational force. The mass in each person’s body also has a gravitational force and that force acts on Earth. Earth has a lot more mass than any one person, animal, or building so Earth’s gravity is stronger and always wins. That’s why things stick to the ground instead of floating through the air! Weight is determined by gravity. No kid on Earth can lift a whole car, but on a planet with less gravity, the car would weigh less and a human could lift it over their head!
Gravity in Our Universe
Gravity is important all over the universe. Without gravity, Earth wouldn’t have a moon! The moon is held in Earth’s orbit through gravity. Losing the moon would create chaos because it’s the gravitational force of the moon that makes oceans and seas have tides! Gravity is also what keeps Earth, and all other planets, in orbit around the sun. Gravity literally holds the planets and stars together in a system.
Scientist Albert Einstein realized that gravity also affects light. Shine a light towards the sky, and the force of gravity makes the light slowly grow red! It’s not possible to see this change with the naked eye, but scientists can measure this effect using special tools.
Gravity can also cause problems. Sometimes the pull of gravity is so strong that light can’t escape the gravitational pull. This happens when a star dies and matter gets squished into a very small space. Black holes can’t be seen without special telescopes. They can also be as small as just one atom! However, that one atom weighs about as much as an entire city! It’s because black holes push so much mass into a tiny space. Larger black holes are known as stellars. Each stellar can have as much mass as twenty suns! Supermassives are the biggest black holes. A supermassive has the same amount of mass as one million suns! Scientists say that each galaxy is organized around a black hole. The black hole in the Milky Way, which is the galaxy where Earth is located, is named Sagittarius A. It’s large even for a Supermassive since it has as much mass as four million suns put together would have!
Gravity on Earth
Life would not survive on Earth if gravity didn’t exist. After all, without gravity, the Earth wouldn’t stay at the right distance from the sun to keep the planet at the correct temperature to allow life to thrive. Gravity even keeps air in the atmosphere so that all the people and animals who live on the planet can breathe. Not every place on Earth has the same amount of gravitational pull.
Why isn’t gravity equal all over Earth’s surface? It’s because places with higher amounts of mass underground have more gravity than places that don’t have as much mass beneath the surface. NASA ran a mission known as GRACE (Gravity Recovery and Climate Experiment) to measure the amount of gravity all over Earth. Maps were created using this data. When looking at a GRACE map, areas in red have stronger gravitational pulls than areas colored blue. The GRACE mission discovered what areas had experienced changes in gravitational pull over time. Earthquakes sometimes cause these changes.
- Physics for Kids: Gravity