# Gravity

Physics is the science that studies motion and matter and how both work with forces and energy.

It is a really big subject that has a lot of different “branches” of scientific study that include motion, sound, waves, electricity, light, sound, and even astronomy. This science covers the tiniest particles and atoms all the way to the largest objects in the universe.

We know gravity as the mysterious force that keeps everything from floating into space and instead makes everything fall towards Earth. One of the things that scientists have discovered is that all objects have gravity, but some objects, such as our Sun and the Earth, have a lot more gravity than other objects.

The amount of gravity doesn’t just depend on the “size” of an object, but instead, it depends on its “mass” as well as how close you are to the object.

The closer that you are to an object the stronger the gravity. The “mass” of an object is basically how tightly compact the molecules and atoms are as well as the number of molecules and atoms.

### Gravity Rules!

Without gravity, everything that we know would just fly away, so it’s incredibly important for our survival and the survival of all species on our planet.

The gravity of the sun is important because it keeps our Earth in a perfect rotation and all life on Earth requires the energy and warmth. Scientists refer to the distance between our Sun and Earth as the “Goldilocks Zone” We aren’t too far away or too close – we are “just right” for life to thrive on Earth.

### Sir Isaac Newton and Einstein

Since they couldn’t see gravity, scientists in the past had to use mathematics to try to explain gravity. Sir Isaac Newton was the first scientist to figure gravity out and he created his “Newton’s law of universal gravitation.”  Many years later, Albert Einstein improved on Newton’s theory in his own “theory of relativity.”

### Weight

You might wonder why different things have different weight? On Earth, weight is the force of gravity on an object or how much force the gravity of our Earth has on the object and how hard it is pulling the object toward the surface.

### Why do two objects fall at the same speed?

If you stand on the roof of a 10-story building and drop two balls, one that weighs 5 lbs and one that weighs 1 lb at the same time, they will both fall towards the ground at the same speed and hit the ground at the same time. This is called the “equivalence principle.” Scientists have defined the letter “g” for standard gravity and it shows that all objects fall at this specific acceleration.

• The tides of our oceans are caused by the gravitational pull of our moon.
• The planet Mars has less mass and is smaller than Earth and has less gravity making a person that weighs 100 lbs on Earth weigh only 38 lbs on Mars.
• Science define 1 g force for standard gravity on Earth, but if you take a roller coaster ride you will feel a lot more g force depending upon how fast and high the roller coaster goes.
• Sky divers depend on what is called “terminal velocity” for a good landing. This is the point where the air’s friction and the force of gravity are equal on an object and will keep a constant speed.
• Fish have “earstones” in their heads that work with gravity to tell them which way is up or down.
• Experiments in space and on the International Space Station have shown that some bacteria taken into space grow better with less gravity.
• The gravitational pull of the moon on our Earth makes the ocean tides, and also makes the oceans “bulge” at the strongest gravitational pull point.

### Q&A:

What does “1 g” stand for?
standard gravity on Earth

What is the reason that one object has stronger gravity than another object?
mass

Who are the two scientists that made the greatest contribution to the topic of gravity?
Sir Isaac Newton and Albert Einstein

What effects does our moons gravity have on the Earth?
creates the ocean tides and ocean bulge

What is the nickname for the location of the Earth in our solar system that makes life possible?
Goldilocks Zone

What would happen if Earth didn’t have gravity?
everything would float into space