Gravity for children
What Is Gravity? | NASA Space Place – NASA Science for Kids
fundamental-physics
Gravity is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun.
What else does gravity do?
Why do you land on the ground when you jump up instead of floating off into space? Why do things fall down when you throw them or drop them? The answer is gravity: an invisible force that pulls objects toward each other. Earth's gravity is what keeps you on the ground and what makes things fall.
An animation of gravity at work. Albert Einstein described gravity as a curve in space that wraps around an object—such as a star or a planet. If another object is nearby, it is pulled into the curve. Image credit: NASA
Anything that has mass also has gravity. Objects with more mass have more gravity. Gravity also gets weaker with distance. So, the closer objects are to each other, the stronger their gravitational pull is.
Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. That's what gives you weight. And if you were on a planet with less mass than Earth, you would weigh less than you do here.
Image credit: NASA
You exert the same gravitational force on Earth that it does on you. But because Earth is so much more massive than you, your force doesn’t really have an effect on our planet.
Gravity in our universe
Gravity is what holds the planets in orbit around the sun and what keeps the moon in orbit around Earth. The gravitational pull of the moon pulls the seas towards it, causing the ocean tides. Gravity creates stars and planets by pulling together the material from which they are made.
Gravity not only pulls on mass but also on light. Albert Einstein discovered this principle. If you shine a flashlight upwards, the light will grow imperceptibly redder as gravity pulls it. You can't see the change with your eyes, but scientists can measure it.
Black holes pack so much mass into such a small volume that their gravity is strong enough to keep anything, even light, from escaping.
Gravity on Earth
Gravity is very important to us. We could not live on Earth without it. The sun's gravity keeps Earth in orbit around it, keeping us at a comfortable distance to enjoy the sun's light and warmth. It holds down our atmosphere and the air we need to breathe. Gravity is what holds our world together.
However, gravity isn’t the same everywhere on Earth. Gravity is slightly stronger over places with more mass underground than over places with less mass. NASA uses two spacecraft to measure these variations in Earth’s gravity. These spacecraft are part of the Gravity Recovery and Climate Experiment (GRACE) mission.
The GRACE mission helps scientists to create maps of gravity variations on Earth. Areas in blue have slightly weaker gravity and areas in red have slightly stronger gravity. Image credit: NASA/University of Texas Center for Space Research
GRACE detects tiny changes in gravity over time.
These changes have revealed important details about our planet. For example, GRACE monitors changes in sea level and can detect changes in Earth’s crust brought on by earthquakes.
If you liked this, you may like:
What Is a Barycenter?
What Is a Black Hole?
What Is a Gravitational Wave?
Gravity | TheSchoolRun
What is gravity?
Gravity attracts all objects towards each other. Gravity has been around since the very beginning of the universe, and it works the same way everywhere in the universe, on all kinds of different objects, of all different sizes (larger than atoms – those are held together by atomic forces instead).
How much gravity an object has depends on how big it is (or to be specific, how much mass it has). It also depends on how close you are to the object; the closer you are, the stronger the gravity.
Gravity is very important to our everyday lives. Without Earth's gravity we would fly right off our planet! We'd all have to be strapped down all the time and if you kicked a ball, it would fly off forever. While it might be fun to try for a few minutes, we certainly couldn't live life on Earth without gravity.
Gravity also is important on a larger scale. It is the Sun's gravity that keeps the Earth in orbit around the Sun. Life on Earth needs the Sun's light and warmth to survive. Gravity helps the Earth to stay just the right distance from the Sun, so it's not too hot or too cold.
Nobody fully understands how gravity works, or even why gravity exists. One way of looking at gravity is to think of it not as a force like magnetism, but instead as a natural result of the way mass bends space. Any object with mass (like a star) pushes on space and bends it, so that other objects (like planets) that are moving in a straight line are also going around the star.
It looks to us like the star is pulling on the planet, but really the star is bending space.
Top 10 facts
- The bigger the object's mass, the more gravity it will have; the smaller the mass of the object, the less gravity it is subject to.
- Gravity guides the growth of plants and other vegetation.
- Black holes have the strongest gravitational pull in the entire universe.
- The Earth is a giant magnet. Its magnetic field is like a bar magnet at its centre.
- Sir Isaac Newton discovered gravity about 300 years ago. The story is that Newton saw an apple fall out of a tree. When this happened he realised there was a force that made it occur, and he called it gravity.
- Ocean tides are caused by the gravity of the moon.
- If you could travel from planet to planet your mass would stay the same, but your weight would vary depending on how the gravity of that planet pulled on you.
Mars is smaller and has less mass than Earth and as a result it has less gravity. If you weigh 100 pounds on Earth, you would weigh 38 pounds on Mars. - At some point when falling, the friction from the air will equal the force of gravity and the object will be at a constant speed. This is called the terminal velocity. For a sky diver this speed is around 100 miles per hour!
- We don't actually "feel" gravity. We only feel the effects of trying to overcome it by jumping or when we fall.
- Gravity always pulls, it never pushes.
Boost Your Child's Maths & English Skills!
- Start your child on a tailored learning plan
- Complete the activities added each week
- Watch your child's maths & English confidence grow!
Trial it for FREE today
Did you know?
- You are shrinking right now. Every day you are taller in the morning than you are at night.
In fact, at the end of each day you are about 1/2 inch (1.25 centimetres) shorter than when you got up that morning. If you don't believe it, have someone measure you when you get up in the morning and then again before you go to bed. This isn't because your heavy backpack has weighed you down. It happens because of gravity. As you walk around during the day, gravity is pulling you down, or more correctly, toward the centre of Earth. Lying down to sleep at night gives your spine a chance to stretch back to your full height. - On Earth, gravity isn't entirely even. Because the globe isn't a perfect sphere, its mass is distributed unevenly, which means slightly uneven gravity.
- One mysterious gravitational anomaly is in the Hudson Bay of Canada. This area has lower gravity than other regions, and a 2007 study found that now-melted glaciers were to blame. The ice that once covered the area during the last Ice Age has long since melted, but the Earth hasn't entirely snapped back from the burden.
Since gravity over an area is proportional to the mass on top of that region, and the glacier's imprint pushed aside some of the Earth's mass, gravity is a bit less strong in the ice sheet's imprint. The slight deformation of the crust explains the unusually low gravity in the area. In some places, it’s almost half as strong as it is elsewhere! - Black holes are some of the most destructive objects in the universe, named because nothing, not even light, can escape their gravitational clutches. At the centre of our galaxy is a massive black hole with the mass of 3 million suns. The black hole isn't really a danger to us Earthlings – it's both far away and it's remarkably calm.
- In the very beginning of the universe, after the Big Bang, gravity pulled atoms together to make stars and planets. Once the stars and planets had formed, gravity kept the planets in orbit around the stars, and moons orbiting around the planets. And on each planet that is large enough, gravity keeps an atmosphere around the planet.
- On Earth, gravity keeps the air around us (and everything else) from drifting off into space. Gravity also causes hot air to rise while colder air falls (which in turn causes wind).
Gravity gallery:
- Astronauts dealing with a lack of gravity!
- As skydivers fall to Earth the force pulling them down is gravity.
- Gravity holds the moon in orbit around Earth
- All objects fall at the same rate – air resistance affects this speed.
- Items with a different mass fall at the same rate in a vacuum.
- It is said that Sir Isaac Newton wrote his theory about gravity after watching an apple fall to the ground.
- A portrait of Sir Isaac Newton.
Gallery
About
Gravity or gravitational forces are forces of attraction. It's like the Earth pulling on you and keeping you on the ground. That pull is gravity at work.
Every object in the universe that has mass exerts a gravitational pull, or force, on every other mass.
The size of the pull depends on the masses of the objects. You exert a gravitational force on the people around you, but that force isn't very strong, since people aren't very big. When you look at really large masses, like the Earth and Moon, the gravitational pull becomes very impressive. The gravitational force between the Earth and the molecules of gas in the atmosphere is strong enough to hold the atmosphere close to our surface. Smaller planets, that have less mass, may not be able to hold an atmosphere.
A larger size does not mean a bigger mass. Imagine two balls that are about the same size, like a football and a bowling ball. Will they have the same mass? No.
An easy way to think about mass is to consider how much matter or "stuff" you can find inside the object. The amount of matter in the object will affect how heavy it is, meaning gravity has plenty of matter to ‘grab onto’. In the case of the football, air molecules make up most of its inside.
The outside of the ball looks solid, but cut it in half and the ball will look like an empty shell. Whereas the inside of a bowling ball is usually completely solid, so if you cut it in half you will end up with two solid pieces. The bowling ball has more matter inside it, making it denser than the football. Therefore, its mass will be greater than the soccer ball's mass.
Mass is measured in grams (g) or kilograms (kg) but is NOT a force. The weight of an object is the force caused by gravity pulling down on the mass of an object. It is measured in newtons (N). Weight is measured using a force meter. The bigger the weight attached to the force meter, the more the spring inside the force meter stretches.
The Earth always produces the same acceleration on every object. If you drop an acorn or a piano, they will gain velocity (speed) at the same rate. Although the gravitational force the Earth exerts on the objects is different, their masses are just as different, so the effect we observe (acceleration) is the same for each.
The Earth's gravitational force accelerates objects when they fall. It constantly pulls, and the objects constantly speed up. You might be thinking, "What about feathers? They fall so slowly." Obviously, there is air all around us. When a feather falls, it falls slowly because the air is in its way. There is a lot of air resistance and that resistance makes the feather move more slowly. The forces at work are the same. If you dropped a feather in a container with no air (a vacuum), it would drop as fast as a baseball.
Isaac Newton was an incredibly clever man. He was a scientist and a mathematician. In 1687, Newton published a book about mathematics which is thought to be one of the important books in the history of science. In it he describes universal gravitation and the three laws of motion, concepts that remained at the forefront of science for centuries after. Newton was known to have said that his work on formulating a theory of gravitation was inspired by watching an apple fall from a tree and wondering about what made it fall downwards.
Words to know:
Universe - all matter and energy that exists in the vastness of space, whether known to human beings or not
Gravity - the attraction due to gravitation that the Earth or another astronomical object exerts on an object on or near its surface
Atoms - the smallest portion into which an element can be divided
Mass - an object has mass (say 100 kg).This makes it heavy enough to weigh 100 kg
Orbit - the path that an astronomical object such as a planet, moon, or satellite follows around a larger astronomical object such as the Sun
Magnetism - the phenomenon of physical attraction for iron, found in magnets or made by a moving electric charge or current
Friction - the rubbing of two objects against each other when one or both are moving
Anomaly - something strange and difficult to identify or classify
Deformation - the act or process of damaging, disfiguring, or spoiling the look of something, or the condition of being damaged, disfigured, or spoiled
Denser - closer together, more tightly-packed
Newtons - The correct unit for measuring force is the Newton, which is abbreviated N.
Force meter - Force meters contain a spring connected to a metal hook. The spring stretches when a force is applied to the hook. The bigger the force applied, the longer the spring stretches and the bigger the reading.
Velocity - the speed at which something moves or happens
Concepts - ideas or principles
Related Videos
Just for fun...
- A tricky gravity game for older children
- Another good game to illustrate gravity
- Find out what you would weigh on other planets
- Compete in the Moon Olympics
- Try some at-home investigations that create microgravity conditions
- Play Gravity, the game
- Experiments to help you find the centre of gravity using paper airplanes and rulers
Best kids' books about gravity
Find out more about gravity:
- A kids' guide to gravity
- Watch BBC Bitesize clips about gravity
- How gravity works
- Watch an animation about gravity and have a go with a gravity simulator
- Find out about microgravity
- See videos for kids about how gravity pulls things down and how the gravitational forces between objects work
See for yourself
Try some practical science experiments: understand more about gravity and explain what you know or try one of TheSchoolRun's at-home science experiments (Experiments and science fun for KS1 and KS2, a subscriber resource).
Watch Expedition 16 flight engineer Dan Tani discuss and demonstrate gravity and Newton's laws from the International Space Station on the NASA website
Also see
What is gravity? - Want to know everything. Science for children and youth
- Details
- Parent category: Cosmos
- Category: Space Publications
Gravity, or gravitation, is the force of attraction between two particles of matter (or two objects) that keeps the planets in their orbits around the Sun or the Moon in its orbit around the Earth.
As the distance between two objects increases, their gravitational attraction decreases.
Gravity is also the force that holds any object on Earth or on any other celestial body, preventing it from flying into space.
The larger the object, the stronger its gravitational attraction, and vice versa.
Since the Moon is much smaller than the Earth, its gravitational pull is only one-sixth that of our planet.
That's why the American astronauts on the moon could easily move in large jumps.
Gravity also explains why the Earth - and other planets and celestial bodies - are generally round. As the solar system formed, gravity pulled dust and gases flying through space together.
When a large amount of matter is collected at the same time in one place, such matter forms a ball, since gravity pulls everything to a central point.
Still, the Earth is not perfectly round. In the process of its rotation around its axis, an additional force arises, under the influence of which the Earth slightly "bulges" in the middle region.
- Views: 1412
- gravity
- gravity
- Back
- Forward
By tags
- What is a black hole?
- home
- Space
- Space Publications
- What is gravity?
Login
Password
Remember me
- Registration
- Forgot login?
- Forgot your password?
Briefly
Which country is the smallest?
The smallest country in the world is the Vatican. The Vatican occupies 44 hectares (108.7 acres), that is, less than half a square kilometer, in the city of Rome, Italy.
The Vatican is the state in which the highest authority of the Roman Catholic Church is concentrated. The Pope also lives here - the supreme person of the Church.
Read more...
Tag cloud
World Ocean the mountains Antarctic thunder cacti smell Belemnites state bites landscape iceberg weight porcupines UN records a wish pyramids tropics Moon fruits
Statistics
- Visitors
- 231
- Materials
- 238
- Number of views of materials
- 1366313
|
|
The closer you are, the stronger gravity. 
