Explain gravity to kids
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?
18 Interesting & Fun Gravity Facts for Kids [2022 Updated]
Please email or share this article!
- FB
Did you know that without gravity, we would fall right off of Earth’s surface and float away?
Or that gravity is the reason a ball comes back down when you throw it into the air, instead of just traveling higher and higher?
What exactly is this mysterious force of nature? Keep reading to find out!
What is gravity?
Gravity is a force of attraction that pulls together all matter (anything you can physically touch).
The more matter something has, the greater the force of its gravity.
That means really big objects like planets and stars have a stronger gravitational pull.
The gravitational pull of an object depends on how massive it is and how close it is to the other object.
For example, the Sun has much more gravity than Earth, but we stay on Earth’s surface instead of being pulled to the Sun because we are much closer to Earth. The gravity of the Sun keeps Earth in orbit around it, keeping us at a comfortable distance.
Who discovered gravity?
For a long time, scientists knew that there was some mysterious force that keeps us on the surface of the Earth.
It wasn’t until 1666 that Isaac Newton first mathematically described the force of gravity, creating Newton’s laws of universal gravitation.
It is said that his ideas about gravity were inspired by watching an apple fall from a tree. Newton wondered what force made the apple fall downward instead of simply floating away.
Another scientist you may have heard of, Albert Einstein, later added to Newton’s ideas about gravity with his theory of relativity.
Why is gravity important?
We already mentioned that we wouldn’t be able to stay put on Earth’s surface without gravity. Objects would simply float away if gravity didn’t exist.
Gravity is also the force that keeps the Earth in orbit around the Sun, as well as helping other planets remain in orbit.
And did you know that weight is based on gravity? Weight is actually the measurement of the force of gravity pulling on an object.
For example, your weight on Earth is how hard gravity is pulling you toward Earth’s surface.
If you traveled to other planets, you would weigh more or less depending on if those planets have more or less gravity than Earth.
Since gravity is related to mass, you know that you would weigh less on smaller planets and more on larger planets.
How is Gravity Measured?
Gravity is usually measured in units of acceleration.
2.
What is the Speed of Gravity on Earth?
At Earth’s surface the acceleration of gravity is about 9.81 m/s2 (32.2 ft/s2).
This means that the speed of an object falling freely will increase by about 9.81 metres (32.2 ft) per second every second.
Does the Moon have Gravity?
Gravity is experienced on the Moon. The acceleration due to gravity on the surface of the Moon is approximately 1.625 m/s2/.
The Moon’s gravity is 1/6 of Earth’s gravity, so objects on the Moon will weigh only 1/6 of their weight on Earth.
So if you weigh 80 pounds (36 kilograms) here on Earth, you would weigh about 13 pounds (six kilograms) on the Moon!
High and low tides in the ocean are caused by the Moon’s gravity.
Facts about Gravity
There is zero gravity in outer space, so you would be weightless if you were floating out in space!
In physics, weight is described as a force and can also be measured in Newtons. Guess who this unit of measurement is named after? That’s right—Isaac Newton, the scientist who discovered gravity.
Objects weigh a little bit more at sea level than they do on the top of a mountain.
This is because the more distance you put between yourself and Earth’s mass, the less gravitational force Earth exerts on you.
So the higher you go, the less gravity pulls on you, and the less you weigh. However, the difference is very small and barely noticeable.
If you wanted to escape Earth’s gravitational pull, you would have to travel seven miles (about 11 kilometers) per second.
This number is called Earth’s “escape velocity.” To travel that fast, you would have to be a superhero!
Even if two objects are different weights, the force of gravity will make them travel at the same speed.
For example, if you dropped balls that were the same size but different weights out of the same second-story window, they would both hit the ground at the same time.
Gravity even helps guide the growth of plants!
Now you know gravity is a major force in the universe.
It keeps us from floating away, controls the ocean’s tides, guides plant growth, keeps Earth and other planets in orbit, and more!
- Physics
- How to make a bouncy ball with things around your house
How to explain gravity to a child - Science
Video: "Why do objects fall down?" / Educational cartoon for elementary grades Formula of the mindContent
- Masses against weight
- Glue, which connects the solar system
- Earth gravity: formidable force
- The secret of the orbital satellite explained
- Interesting facts about gravity
“This is forcing things fall", children can answer if you ask what gravity does. They may have a little more trouble telling you what this mysterious power really is. Scientists don't fully understand it either, but in simple terms, gravity is an invisible force of attraction that causes objects to move towards each other. However, Voyager 1, launched at 1977, has escaped the Earth's gravitational pull and is visible proof that what goes up doesn't have to come back down.
Mass versus weight
Every object has a mass, a basic property that measures the amount of matter an object possesses. If an object does not approach the speed of light, its mass does not change. As the mass of an object increases, so does its gravitational attraction. This is why very large objects, such as the planet Jupiter, have a greater gravitational pull than the moon, which is a much smaller celestial body. Tell the children that they weigh more on Earth than on the Moon because of the difference in gravity between the two objects.
Glue that binds the solar system
Planets can look like tiny twinkling stars to children, even if they are large objects that move through space under the influence of gravity. Enlighten the children by showing them a scale model of the solar system or a photograph of one with the sun at its center. Talk about how this star's massive gravitational pull pulls planets towards it, even if they never hit the sun. Bodies in the solar system remain in orbit due to their motion around their star.
If the sun were to suddenly disappear, the Earth and other planets would fly off into space in different directions without the sun's gravity to hold them back.
Earth's gravity: a formidable force
Bring the discussion of orbits and gravity closer to home by describing how satellites revolve around the Earth the way the Earth and its sister planets revolve around the Sun. Because the Earth is large and has mass, it has a strong gravitational field that causes objects to fall towards its center in the same way that a severed apple falls to the ground from a tree. The International Space Station - which a child may have seen on TV - is one popular example of an object moving rapidly around the planet while falling at the same time. The Moon is another body that falls around the Earth approximately every 27 days. Its gravity, along with the suns, pulls the earth's waters, causing tides.
The secret of the orbiting satellite explained
If the Earth's gravity pulls objects towards it, you might think that you see planets leaving for the sun and satellites falling to Earth.
This does not happen because objects in orbit are moving fast enough at right angles to the planet to "fall" around the body they are orbiting. Help your child understand this important concept by having him wrap something around his head with a string. The string - the force of gravity - pulls the object towards the child, while the object's forward motion or velocity - pulls it outward and keeps it from being fully pulled by the string inward. Ask the child to stop spinning the object and notice how, without moving forward, the object will eventually slow down and fall.
Interesting facts about gravity
Sir Issac Newton, a brilliant scientist, discovered many important things about gravity and motion. For example, he found that the gravitational force between two objects is inversely proportional to the square of the distance between their centers. In other words, if a child is standing on top of Mount Everest, the gravitational pull between her and the center of the earth is less than when she is standing on the ground.
A highly sensitive balance can detect subtle differences in weight between an object that moves between two different heights. Objects also accelerate at a constant rate as they fall towards the ground. When a child throws an object from a tall building, it will increase its speed every second.
What is gravity and how it works, in simple words
Since ancient times, people have thought about what force attracts objects to the Earth. Such great minds as Newton and Einstein tried to explain the phenomenon of gravity, but it still remains not fully understood
Gravity (from Latin gravis, “heavy”) is a force that attracts two bodies to each other. Everything that has matter, that is, everything that can be touched, also has a gravitational attraction. Gravity is one of the four fundamental forces in the universe along with electromagnetism and the strong and weak nuclear forces. Although it is the weakest force, it is the most visible. Due to the work of the gravitational force, people can walk on the Earth, and planets can orbit around the Sun.
The gravity of any object is proportional to its mass. Thus, objects with more mass have more gravity. Since the Earth is the largest and closest object around, then all objects and objects are attracted to it. For example, apples fall to the ground, and are not attracted, for example, to a person's head.
The moon is attracted to the Earth as an object with a larger mass (Photo: Shutterstock)
Distance also affects gravity. The further away the object, the weaker the gravitational attraction.
Ancient scientists, trying to describe the world, came up with their own explanations for why objects fall to the ground. The ancient Greek philosopher Aristotle argued that objects have a natural tendency to move towards the center of the universe, which he believed was in the middle of the earth.
However, the Pole Nicolaus Copernicus in the 16th century realized that the trajectories of the planets in the sky are determined by the position of the Sun, which is the center of the solar system.
A century later, the British mathematician and physicist Isaac Newton expanded on the ideas of Copernicus and concluded that because the Sun attracts the planets, all objects are attracted to each other.
Einstein's general theory of relativity is the current theory of gravity today.
Newton's classical theory of gravitation
The English physicist Isaac Newton said that the idea of universal gravitation came to him while walking. He was walking through the apple orchard on his parents' estate and suddenly saw the moon in the daytime sky, and then an apple broke off from a branch and fell to the ground. By that time, Newton was already working on the laws of motion and understood that the apple fell under the influence of the Earth's gravitational field. He also knew that the Moon does not occupy a static position in the sky, but rotates in orbit around the Earth, that is, it is affected by some kind of force that prevents the satellite from flying into space.
The physicist realized that perhaps the same force acts on the apple and the moon.
Newton's predecessors thought differently. The Italian physicist Galileo Galilei believed that natural attraction acts on the Earth. The German astronomer Johannes Kepler believed that completely different laws of motion operate in the celestial spheres than on Earth. Newton combined these two types of gravity in his mind.
Newton's law of universal gravitation, formulated by him in 1687, states that between any pair of bodies in the universe there is a force of mutual attraction. It is expressed by a mathematical equation: if M and m are the masses of two bodies, and r is the distance between them, then the force F of mutual gravitational attraction between them is F = GMm / r², where G is the gravitational constant equal to the force with which they act on each other other bodies with masses of 1 kg each, being at a distance of 1 meter from each other. The equation says that force (F) is proportional to the masses of two objects divided by the square of the distance between them.
It follows from this that the more massive the objects, the greater the force of attraction between them, but the farther they are from each other, the weaker the attraction.
Newton's law of gravity (Photo: praxilabs.com)
The law applies to all physical material bodies without exception in the Universe. The force of gravity of the Earth at its surface equally affects all material bodies located anywhere on the globe. Each person is affected by the force of gravity, which is felt as a weight.
Newton's law of universal gravitation says that not only the Earth attracts the apple, but the apple also attracts the Earth. But the huge mass of the Earth means that it takes a lot more force to move it a palpable amount, so the apple falls and the Earth remains virtually stationary. The same is true in a wider context. Every object in the universe attracts every other object, and the closer and more massive it is, the greater its gravitational force.
According to Newton, the force of attraction acts at any distance and instantly. However, the fastest speed in the world is the speed of light, and to overcome large distances, light needs not an instant, but several seconds and sometimes even years.
Einstein's Theory of Gravity
In 1798, British physicist Henry Cavendish performed one of the world's first high-precision experiments to try to accurately determine the value of G, the gravitational constant. He built the so-called torsion balance by attaching two small lead balls to the ends of a beam suspended horizontally by a thin wire. Next to each of the balls, the physicist placed a large spherical lead weight. Small lead balls were gravitationally attracted to heavy lead weights, causing the wire to twist slightly. This phenomenon allowed him to calculate the value of G. 92. To get an accurate value, scientists must develop incredibly sensitive equipment.
The German-American physicist Albert Einstein brought about the next revolution in our understanding of gravity.
His general theory of relativity showed that gravity arises from the curvature of spacetime, meaning that even light rays that should follow this curvature are refracted by extremely massive objects. Within the framework of his theory, gravity is considered not as a force that acts on bodies, but as a curvature of space and time under the influence of mass and energy.
Einstein's theories were used to suggest the existence of black holes - celestial objects with such a large mass that even light cannot escape from their surface. Near a black hole, Newton's law of universal gravitation can no longer accurately describe how objects move.
The theory that Einstein published in 1915 extended his theory of special relativity, which the scientist had developed a decade earlier. Special relativity claimed that space and time are inextricably linked, but this theory did not recognize the existence of gravity.
In his theory of special relativity, Einstein determined that the laws of physics are the same for all non-accelerated observers and showed that the speed of light in vacuum is the same regardless of the speed at which the observer is moving.
As a result, he discovered that space and time are intertwined, and events that occur at the same time for one observer may occur at different times for another.
While developing the equations of his general theory of relativity, Einstein realized that massive objects cause a distortion of space-time. Imagine that you are placing a large object in the center of a trampoline. The object was pressed into the tissue, causing dimples to appear. If you then try to roll the ball around the edge of the trampoline, it will spiral inward towards that object.
The rotation of a heavy object such as the Earth must twist and warp space-time around it. In 2004, NASA launched the Gravity Probe B gravitational probe. According to the agency, the axes of the satellite's finely calibrated gyroscopes drifted very little over time, consistent with Einstein's theory.
Einstein predicted that events such as the collision of two black holes create ripples in space-time known as gravitational waves.
And in 2016, the Laser Interferometric Gravitational Wave Observatory (LIGO) announced that it had detected such a signal for the first time. The gravitational wave was caused by the collision of two black holes with a mass of 29and 36 times the mass of the Sun. After that, they merged into one big black hole. This happened, presumably, 1.3 billion years ago.
Gravitational waves created by two colliding black holes (Photo: R. Hurt/Caltech-JPL)
Since then, LIGO and its European counterpart Virgo have detected a total of 50 gravitational wave events.
What is the force of gravity
The gravitational field of the Earth is the field of gravity, which is formed due to the gravitational force of the Earth and the centrifugal force caused by its daily rotation.
Gravity on the Earth's surface varies from 9.780 m/s² at the equator to 9.
832 m/s² at the poles. In approximate calculations, the value is usually taken equal to 9.81; 9.8 or 10 m/s². However, it takes into account only the force of gravity and does not take into account the centrifugal force arising from the rotation of the Earth. As the body rises above the Earth's surface, the value decreases.
NASA has created a visualization of gravitational anomalies on Earth as part of the GRACE project. Areas where gravity is stronger are shown in red, where it is weaker than standard values in blue. (Photo: NASA)
French scientists claim that the difference in the gravitational constant in different regions of our planet depends on the strength of the Earth's magnetic field. They suggested that such an influence could be explained by the presence of additional dimensions of space hidden from direct observation. Scientists have calculated that the Earth's gravity will be stronger in those places where the magnetic field is stronger.
Thus, it reaches its maximum values in the regions of the north and south magnetic poles. They do not coincide with geographic poles. So, the north magnetic pole is located within the boundaries of the current Canadian Arctic, and the south lies on the edge of Antarctica.
If we take the value of gravity on Earth as a unit, then on the Sun it will be equal to 27.9, on Mercury - 0.37, on Venus - 0.9, on the Moon - 0.16, on Mars - 0.37, on Jupiter - 2.6. Thus, if a person who weighs 60 kg on Earth weighs on Jupiter, the scale will show 142 kg.
Astronauts in orbit also experience microgravity. They seem to fall endlessly along with the ship in which they are.
Modern understanding of gravity
Scientific research in the field of gravity continues. Einstein's theory of relativity explains some of the anomalies in Newtonian gravity; however, discoveries in atomic, nuclear and elementary particle physics have shown that it cannot be attributed to interactions in quantum physics.
Simply put, Einstein's theory does not work in the microcosm. In this regard, the direction of "quantum gravity" or the quantum description of gravitational interaction has been developed.
However, the theory of quantum gravity has not yet been built. The main difficulty is that the two physical theories it tries to tie together—quantum mechanics and general relativity—are based on different sets of principles. The first describes the temporal evolution of physical systems (for example, atoms or elementary particles) against the background of external space-time. In the second, there is no external space-time at all - it itself is a dynamic variable in the theory.
There are two main areas of development in quantum gravity: string theory and loop quantum gravity. In the first theory, instead of particles and background space-time, there are strings and their high-dimensional counterparts, branes.
In the second, an attempt is made to formulate a quantum field theory without reference to the space-time background; space and time according to this theory consist of discrete parts.
These are small quantum cells of space that are connected to each other in a certain way, so that on small scales of time and length they create a discrete structure of space, and on large scales they smoothly turn into a continuous smooth space-time. It is assumed that it is loop quantum gravity that can describe the very process of the explosion that preceded the formation of the Universe.
Since the 1980s, Pennsylvania State University has been developing a paradigm based on the notion of loop quantum gravity. It describes all modern large structures in the Universe as quantum fluctuations of space-time that took place at the birth of the world.
The existing theory of the Big Bang, as already mentioned, does not explain what happened before the birth of the Universe. Scientists from Pennsylvania hold to the alternative Big Rebound hypothesis, according to which the current expanding universe arose from the collapse of the previous universe. To describe this state, they combined quantum mechanics and the theory of relativity.
The authors of the work claim that they were able to describe the cosmic radiation that arose immediately after the birth of the universe. They stated that quantum threads were woven into Einstein's fabric of space-time. It is this that in the future may make it possible to explain why galaxies and matter are unevenly distributed in the Universe.
In the 1990s, astronomers discovered that the expansion of the universe was accelerating. This contradicts the predictions of the general theory of relativity, according to which gravity should slow down the expansion. To explain this phenomenon, cosmologists have begun referring to "dark energy," a force that makes up nearly three-quarters of the matter and energy in the universe and therefore pushes it apart. But the origin of dark energy remains a mystery to this day. Some researchers are trying to explain the acceleration of the expansion of the universe without dark energy, suggesting that if the general theory of relativity is wrong, and gravity is weakening on a cosmic scale.
But so far no one has come up with a way to test this theory.
There is also such a thing as anti-gravity - a supposed counteraction that extinguishes or even exceeds the gravitational attraction by repulsion.
The current approach to anti-gravity is to release the object from the force of gravity so that it is not subject to gravity for some time. For example, the flight of a person in a wind tunnel is ensured by the fact that the force of gravity is counteracted by the flow of air.
Wind tunnel flight (Photo: FlyStation)
So far, the question of the existence of antigravity as an independent phenomenon remains open, since the phenomenon of gravity itself is only being studied.
How to overcome gravity
To overcome the force of Earth's gravity, the body must have a speed equal to 7.91 km/s. This is the first cosmic speed.
It is enough for the object to move in orbit around the planet. To escape the Earth's gravitational field, a spacecraft must have a speed of at least 11.2 km/s. This is the second space velocity. To go beyond the boundary of the sphere of gravity, which ends at a distance of about 930 thousand km from the Earth, the speed of the object should be about 16.6 km / s. This is the third space velocity.
If there were no gravity
In accordance with the above laws of physics, in practice, such a situation is impossible.
Former NASA astronaut physicist Jay Bucky notes that our body is adapted to the force of gravity. When gravity almost disappears (for example, on board the ISS), the body begins to rebuild. During missions in space, ship crew members lose bone mass and muscle tone, as well as a sense of balance.
Dr. Kevin Fong adds that the number of red blood cells in the body drops, which leads to the so-called space anemia. At the same time, wounds heal longer, and immunity also decreases, and there are problems with sleep.
Thus, in the absence of gravity, muscles, the vestibular apparatus, the heart, and blood vessels would develop differently.
Astronomer Karen Masters of the University of Portsmouth in the UK suggested that in the absence of gravity, the Earth would begin to rotate at a high angular velocity like a rope untwisted overhead. Thus, any objects on the planet would fly straight into space, just like water with the atmosphere. Only fortified structures could stay on the surface of the Earth for some time.
Ultimately, the lack of gravity will destroy the planet itself. The earth will break into pieces, which will scatter in different directions.
A similar example, but with the Sun, is given by the Discovery News channel in its video.
What happens if gravity is no longer
Without gravity, there would be no stars or planets, and the Universe would become a mixture of scattered atoms and molecules.
Is artificial gravity possible
When a person finds himself in space, far from the gravitational effects experienced on the surface of the Earth, he experiences weightlessness.
Although all the masses of the Universe will continue to attract him, they will continue to attract the spaceship, so the person, as it were, "floats" inside it. In this regard, the question arises - how to create conditions of artificial gravity, under which a person will be able not to fly, but to calmly walk around the spacecraft?
So far, the desired effect can only be obtained through acceleration. In the case of a spaceship, make it rotate. Then you can get centrifugal thrust, as on Earth. But to travel to another star system, you will have to speed up the ship on the way there and slow it down when you arrive back. The human body is unlikely to be able to endure such loads. For example, in order to accelerate to "impulse velocity" like in the movie Star Trek, to a few percent of the speed of light, you would have to sustain an acceleration of 4000 g (units of acceleration caused by gravity) for an hour. This is 100 times the acceleration that prevents the flow of blood in the human body.
Roscosmos is exploring the idea of a built-in centrifuge on board the spacecraft, which cosmonauts can periodically enter to experience gravity and reduce the negative effects of being in zero gravity.
Still from Star Trek (Photo: YouTube)
Artificial gravity was supposed to be possible with a negative gravitational mass, which is expected to be inherent in antimatter. However, the European Organization for Nuclear Research (CERN) found that the inertial mass of the antiproton (the "mirror image" of the proton, which differs in signs of all characteristics of the physical interaction) coincides with the mass of the proton. If gravity had acted differently on antiprotons, physicists would have noticed the difference. It turns out that the effect of gravity on antiprotons and protons is the same. In addition, antihydrogen, the first stable form of antimatter, was obtained at CERN.
