Space Flashcards
(20 cards)
What causes gravity?
Gravity is caused by mass. All objects with mass attract each other. The more mass something has, the stronger its gravitational pull.
Why do astronauts float in space?
They’re in constant free fall around Earth. There’s still gravity, but they’re falling at the same rate as the spacecraft.
Why does the Moon orbit Earth instead of flying away?
Earth’s gravity pulls it in while the Moon’s sideways speed keeps it moving around Earth instead of crashing into it.
What is a satellite?
A satellite is any object that orbits another object in space. The Moon is a natural satellite; artificial satellites are made by humans.
What keeps planets in orbit around the Sun?
The Sun’s gravity pulls the planets in, and their forward motion keeps them moving in a curved path around it.
Why is there no atmosphere in space?
There’s no air because space is a vacuum — there aren’t enough gas particles, and there’s no surface to hold an atmosphere together like Earth’s gravity does.
What is a light-year?
It’s the distance light travels in one year — about 9.46 trillion km. It’s used to measure huge distances between stars and galaxies.
What’s the difference between a star and a planet?
A star produces its own light through nuclear fusion. A planet doesn’t — it reflects light and orbits a star.
Why do we have seasons on Earth?
Because the Earth’s axis is tilted. As Earth orbits the Sun, different parts get more direct sunlight at different times of year.
What’s the difference between a day and a year on Earth?
A day is one full rotation (24 hours). A year is one full orbit around the Sun (365.25 days).
Why does gravity get weaker the farther you go from an object?
Because gravitational force follows the inverse-square law — it decreases with the square of the distance. If you double the distance the force becomes 1/4 as strong.
What is escape velocity and why do rockets need to reach it?
Escape velocity is the minimum speed needed to break free from a planet’s gravity without falling back. For Earth, it’s about 11.2 km/s. Rockets must reach this to enter space.
How does the balance between gravity and orbital speed keep satellites in orbit?
Gravity pulls the satellite toward Earth while its forward speed keeps it from falling — this creates a stable curved path: orbit.
Why do astronauts need pressurised suits in space?
Because in a vacuum, low pressure would cause body fluids to boil. The suit keeps pressure around the body.
How do spacecraft maneuver in space without air?
They use thrusters that eject mass (like gas or ions) in one direction, pushing the craft the opposite way — Newton’s third law.
Why do planets orbit the Sun in the same direction and plane?
Because they formed from the same spinning disc of gas and dust. Conservation of angular momentum caused the material to flatten and spin in one direction.
What is redshift and what does it tell us about the universe?
Redshift is when light from distant galaxies stretches to longer wavelengths making it appear redder. It shows the universe is expanding.
Why don’t we feel the Earth spinning?
Because it spins at a constant speed, and we move with it just like you don’t feel motion in a smooth airplane flight.
How does the Moon cause tides on Earth?
The Moon’s gravity pulls on Earth’s oceans. The side closest to the Moon bulges out from the stronger pull, and the far side bulges from inertia, creating two tides.
What would happen to Earth’s orbit if the Sun’s gravity suddenly disappeared?
Earth would fly off in a straight line at its current speed — no gravity means no centripetal force to keep it in orbit.
