knowversePhysics myths about gravity and motion: can you tell which ones are true?
Most popular physics myths come from trusting what motion feels like instead of what forces actually do. This page lists ten claims about gravity, orbits and curved motion for you to mark before checking the facts.
Many of these ideas feel obviously true from everyday life, which is exactly why they stick around. Read through each claim, test your intuition, and see how your guesses hold up against real physics.
Physics myths: myth or fact?
Mark each claim as a myth or a fact. The answers stay hidden until you check them all.
- Claim 1
There is no gravity in space, which is why astronauts float.
It is a myth
Gravity is very much present in space, and it does not vanish just because you leave the ground. In fact, gravity at the altitude of the International Space Station is about 90% as strong as it is on the ground. This means a paperclip left at station height would still feel nearly the same pull from Earth as it does sitting on a desk.
Source excerpt
Yes, gravity is very much present in space. In fact, gravity at the altitude of the International Space Station is about 90% as strong as it is on the ground.
From the Knowverse course text.
- Claim 2
Two pencils lying on a desk are pulling on each other right now.
It is a fact
Every object with mass attracts every other object through gravity, which means that right now, you are pulling on the Earth, and two pencils sitting on a desk are actually pulling toward each other. The pull between ordinary office supplies is just far too weak to notice without a planet-sized mass helping out.
Source excerpt
This means that right now, you are pulling on the Earth, and two pencils sitting on a desk are actually pulling toward each other.
From the Knowverse course text.
- Claim 3
A heavy cannonball falls faster than a light marble dropped at the same moment.
It is a myth
Ignoring air resistance, a heavy cannonball and a light marble dropped together will hit the ground together. Mass does not speed up a fall in a vacuum, meaning a bowling ball and a tiny pebble land at the exact same instant when dropped from a tower.
Source excerpt
A heavy cannonball and a light marble dropped together will hit the ground together.
From the Knowverse course text.
- Claim 4
A bullet fired horizontally and a bullet dropped from the same height hit the ground at the same time.
It is a fact
They hit at the exact same time because gravity pulls them both downward equally, regardless of how fast one is moving forward. Horizontal and vertical motion are entirely independent, so firing a rifle horizontally leaves its downward drop completely unchanged.
Source excerpt
They hit at the exact same time. Gravity pulls them both downward equally, regardless of how fast one is moving forward.
From the Knowverse course text.
- Claim 5
Move three times farther from a planet and its pull on you drops to one-ninth.
It is a fact
If the distance between two objects triples, the gravity between them drops to one-ninth of the original pull. This happens because gravity follows an inverse-square law where three squared equals nine, spreading the force over an area that grows with distance.
Source excerpt
If the distance between two objects triples, the gravity between them drops to one-ninth of the original pull.
From the Knowverse course text.
- Claim 6
In a sharp turn, centrifugal force pushes you toward the outside of the car.
It is a myth
The outward force you feel is actually a result of inertia, which is the tendency of an object to maintain its current motion. Your body wants to keep going straight while the car door pushes you inward to make you turn, which makes a passenger slide across a vinyl seat.
Source excerpt
The outward 'force' you feel is actually a result of inertia, which is the tendency of an object to maintain its current motion.
From the Knowverse course text.
- Claim 7
Astronauts feel weightless because they are falling the whole time.
It is a fact
Astronauts feel weightless because they are in a state of continuous free-fall. Since they and their spacecraft are falling toward Earth at the exact same rate, there is no floor pushing up against them, creating the same sensation as a fast drop on an amusement park ride.
Source excerpt
Astronauts feel weightless because they are in a state of continuous free-fall. Since they and their spacecraft are falling toward Earth at the exact same rate, there is no 'floor' pushing up against them.
From the Knowverse course text.
- Claim 8
A thrown ball keeps moving forward only because a force keeps pushing it.
It is a myth
After the initial toss, no horizontal force acts on it, ignoring air resistance. It moves forward only because of its inertia, continuing along its path until gravity and air slow it down.
Source excerpt
No. After the initial toss, no horizontal force acts on it (ignoring air resistance). It moves forward only because of its inertia.
From the Knowverse course text.
- Claim 9
Let go of a ball you are swinging on a string and it flies straight outward, away from the centre.
It is a myth
It does not fly out radially because there is no force pulling it that way once released. It flies tangentially in a straight line, following the exact direction it was heading the millisecond the string let go.
Source excerpt
It doesn't fly 'out' (radially) because there is no force pulling it that way. It flies tangentially (in a straight line).
From the Knowverse course text.
- Claim 10
A satellite in a circular orbit keeps the same speed, even though gravity pulls on it all the time.
It is a fact
In a perfectly circular orbit, the speed of a satellite actually remains constant. Gravity pulls toward the centre perpendicular to the sideways motion, changing the direction of travel without ever speeding up or slowing down the craft.
Source excerpt
In a perfectly circular orbit, the speed of a satellite actually remains constant.
From the Knowverse course text.
Questions people ask
Why don't we feel gravity pulling between everyday objects?
Every object attracts every other object, but the gravitational pull between everyday items like pencils or books is far too weak to notice without a planet-sized mass.
Does gravity ever reach zero?
Gravity gets weaker as you move farther away following an inverse-square law, but it never truly drops to zero no matter how far you travel into space.
What happens if a satellite goes faster than its orbital speed?
If a satellite exceeds its required orbital speed, its path stretches out into a larger ellipse rather than staying in a neat circle.
Take the next step and learn the topic properly in the Knowverse course Curved Motion and Gravity. Work through the concepts step by step to see how forces shape orbits and daily motion.
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Sources: Curved Motion and Gravity. Each claim is settled by an excerpt from the course.