Gravity
Have you ever wondered why everything that goes up must eventually come down? It is not just a random rule of nature. It is a massive, invisible force pulling you towards the exact centre of the Earth! Let us dive into the heavy science of gravity and discover what holds the entire universe together.
What Keeps Your Feet Firmly on the Ground?
Not exactly! There is no real "down" in space. Gravity actually pulls everything towards the exact centre of an object's mass. This is why people in Australia do not fall off the bottom of the Earth!
No, it exists everywhere! Absolutely everything with mass has gravity, including you! Your body is currently pulling gently on everything in the room around you, but the Earth is just so massive that its pull overrides yours.
Put Your Instincts to the Test
Think about what you already know about falling objects and space. Pick an answer for each question, then see if your instincts were right.
They both hit at the exact same time! Gravity pulls all objects and makes them accelerate at the exact same rate, no matter how heavy they are.
Because gravity pulls equally towards the centre! When a planet has enough mass, gravity crushes it from all sides into a perfectly round ball.
On Jupiter! Because Jupiter is incredibly massive, its gravitational pull is significantly stronger than Earth's, making you feel overwhelmingly heavy.
Understanding the Science
Let us break down the invisible forces, falling objects, and massive celestial bodies with Bill Nye the Science Guy.
Key Concepts
Gravity
Tap to learn moreGravity is the invisible pulling force that exists between all objects with mass. It is what keeps us on the ground and holds the moon securely in the sky.
Mass
Tap to learn moreMass is the absolute amount of matter or "stuff" inside an object. The more mass an object has, the stronger its gravitational pull becomes.
Weight
Tap to learn moreWeight is a measurement of how strongly gravity is pulling on your specific mass. Your mass stays the exact same everywhere, but your weight changes depending on what planet you visit!
Acceleration
Tap to learn moreAcceleration is the rate at which a falling object speeds up. On Earth, gravity accelerates all falling objects at a constant speed, completely regardless of how heavy they are.
Orbit
Tap to learn moreAn orbit is the circular path an object takes around a much more massive object. The Earth stays in orbit around the Sun because the Sun's massive gravity constantly pulls on it like an invisible tether.
Sphere
Tap to learn moreA sphere is the natural shape of all planets and stars. Gravity pulls matter equally from all sides towards the very centre, forming a beautifully perfect round ball.
Air Resistance
Tap to learn moreAir resistance is the upward friction caused by air molecules pushing against a falling object. A flat piece of paper falls slower than a crumpled one only because the air catches its wide surface.
Microgravity
Tap to learn moreMicrogravity is the unique feeling of weightlessness astronauts experience in space. They are not free from gravity; they are just falling completely around the Earth at the exact same speed as their spaceship!
Try It: Interactive Planetary Drop Zone
Test Galileo's famous experiment across the solar system! Use the yellow slider to select a celestial body, then press Drop to release an apple and a bowling ball at the exact same time. Notice how the pull of gravity changes their acceleration!
Apply Your Knowledge
Let us see if you can match these gravitational effects to their real-world examples.
Match the Concepts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are designing a brand new sport to be played on the Moon. Because the Moon has only one-sixth the gravity of Earth, how would you specifically design the playing field, the ball, and the scoring system to make the game fun and challenging?
What Has Changed Since This Episode Aired
This episode first aired in 1993. While objects still fall to the ground at the exact same speed, our advanced understanding of gravity across the universe has completely evolved!
Updated: Yes! In 2015, scientists successfully detected gravitational waves for the very first time. When two massive black holes collided over 1.3 billion light years away, they sent violent, invisible ripples through the fabric of the universe that we measured right here on Earth.
Updated: Actually, it is slightly lumpy! Advanced satellites like the GRACE mission have meticulously mapped Earth's gravity and found it varies. The gravitational pull is slightly stronger over incredibly dense mountain ranges and slightly weaker over deep, empty ocean trenches.
Updated: In 2019, scientists successfully captured the very first actual photograph of a supermassive black hole in the galaxy M87! Its gravity is so unimaginably powerful because the black hole is an astounding 6.5 billion times more massive than our Sun.
Test Your Understanding
Answer these questions and get instant feedback. How many can you get right?
Results
Your score:
Reflection
Gravity connects everything in the universe, from the apple falling from a tree to the moon orbiting our planet. If you could temporarily turn off gravity in your bedroom for ten minutes, what is the very first experiment you would try?
Episode Discussion
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