What is Gravity?

Kam’s question about g force has led me to write about gravity first. The g force post will be our next post.

What is Gravity?

Gravity is a force, here attracting or pulling objects to Earth

Gravity is the force that keeps us on Earth’s surface.

  • Without the force of gravity, we would fall off and float away from beloved planet Earth, with it we are safely grounded.
  • When you throw a ball in the air, gravity makes it fall back to Earth, then you can catch it.
  • Some objects, like the Earth and the Sun, have more gravity than others.
  • Tides are caused by the rotation of the Earth and the gravitational effects of the Moon and Sun.
  • Life on Earth could not exist without gravity.

All objects with mass have gravity.  The amount of gravity an object has depends on its size – or 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 keeps Earth, other planets and moons in our solar system in orbit around the Sun.  It also keeps the Moon in orbit around Earth.

Gravity helps Earth to stay at just the right distance from the sun.  Planet Earth needs the Sun’s light and heat so that our wonderful Planet and life forms exist.

Watch the ball, catch the ball.

Without gravity would we have to wear heavy boots or be attached to a rope, attached to Earth?  Would everything else float away?  How would water or soil stay on Earth? How would we live and survive?

Did Brian Cox discover Gravity?

Isaac Newton

No.  Brian Cox didn’t discover gravity but he is an expert on gravity and how it works.

Gravity was discovered or worked out by Isaac Newton. His theory is called Newton’s law of universal gravitation and is great for most situations.

Albert Einstein made further discoveries to expand Newton’s works.  Today, modern physicists and scientists use Albert Einstein’s general theory of relativity to describe gravity.

Albert Einstein
Albert Einstein

More about Gravity

Gravity is a force that attracts or pulls objects toward the Earth. In Newton’s Law of Universal Gravitation, gravitation is the force that attracts objects toward each other.

One of the keys things about the force of gravity is that all objects fall at the same rate, independent of mass and air resistance.

(Think about a feather falling and stone falling, the difference in speed to fall is because of air resistance, not because of the difference in mass.)

Remember, the acceleration due to gravity, g, is a constant for all objects, no matter what their mass.

Gravity and the Planets

Gravity on the Moon and on other planets have different values of acceleration due to gravity. However, the effects of the force are similar.

The force of gravity on the Moon is about 1/6 of that on the Earth for a given mass.  The value for gravity on the moon  is approximately 1/6 of the value for g on Earth. Thus, an object on the Moon would weigh about 1/6 of its weight on earth. other planets work on the same principal, although their force of gravity values differ.

Objects dropped on the moon, of different weight, would fall to the ground at the same rate, just slower than on Earth.  There is no air resistance on the moon as there is no air on the Moon.

Projectiles, satellites, planets, galaxies, and clusters of galaxies are all influenced by Gravity.

A Note to You and Me

Kam and I are going to do a little experiment:

When we are out we are going to find a stone and a heavier stone and drop them at the same time, from the same height. We hope they will hit the ground at the same time. This may or may not provoke more questions, we’ll see.  Why then does a feather take longer to fly than a stone? – air resistance.

As ever, if you read this post and would like to comment, please do.  If I have missed the point, please let me know, otherwise Kam will miss the point too!


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