Science Facts
102 flashcards by MentisLibrary
Checkable facts from physics, chemistry, biology, astronomy, earth science, the human body and measurement, each with its field, why it matters and the confusion it usually causes.
- What is the smallest unit of life?
- The cell. Everything alive is either a single cell or an organised collection of them.
- What is photosynthesis?
- Plants, algae and some bacteria use light energy to turn carbon dioxide and water into sugar, releasing oxygen as a by-product.
- What is osmosis?
- Water moving through a semi-permeable membrane from where dissolved substances are dilute toward where they are concentrated.
- What is an enzyme?
- A protein that speeds up a specific biological reaction without being consumed by it.
- What is the greenhouse effect?
- Gases such as carbon dioxide, methane and water vapour let sunlight in but absorb the infrared heat the surface radiates back, warming the lower atmosphere.
- What is natural selection?
- Individuals vary; some variants survive and reproduce better in a given environment; those traits become more common over generations.
- What is a black hole?
- A region where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon.
- How fast does light travel in a vacuum?
- Exactly 299,792,458 metres per second, close to 300,000 km per second. No information can travel faster.
- Why is the sky blue?
- Air molecules scatter short blue wavelengths far more strongly than long red ones, so blue light arrives at your eye from every direction.
- Why do sunsets look red?
- At sunset the light takes a long slanted path through the atmosphere, so most of the blue has already been scattered away before it reaches you.
- State Newton's first law of motion.
- An object stays at rest, or keeps moving in a straight line at constant speed, unless a net force acts on it.
- State Newton's third law of motion.
- Forces always come in pairs: if A pushes on B, B pushes back on A with equal size and opposite direction.
- What does the first law of thermodynamics say?
- Energy is never created or destroyed, only converted between forms.
- What does the second law of thermodynamics say?
- The total entropy, or disorder, of an isolated system never decreases.
- Kinetic energy versus potential energy
- Kinetic energy is the energy of motion; potential energy is stored energy an object has because of its position or state.
- Why does ice float on water?
- Water is one of the few substances that expands when it freezes, so ice is about 9 percent less dense than liquid water.
- How fast does sound travel in air?
- About 343 metres per second in dry air at 20 degrees Celsius, roughly a million times slower than light.
- What is the Doppler effect?
- The change in a wave's observed frequency when the source and the observer move relative to each other.
- What is Archimedes' principle?
- The upward buoyant force on a body in a fluid equals the weight of the fluid the body displaces.
- What is terminal velocity?
- The steady speed a falling object reaches when air resistance grows large enough to balance its weight.
- How hot is a lightning bolt?
- The channel can reach about 30,000 kelvin, roughly five times the temperature of the Sun's visible surface.
- Why does a straw look bent in a glass of water?
- Light changes speed when it passes between water and air, so it bends at the surface and the straw appears displaced.
- Does an astronaut's mass change on the Moon?
- No. Mass is the amount of matter and does not change; weight is the force of gravity on that mass, and on the Moon it is about one sixth of Earth's.
- What is an atom made of?
- A dense nucleus of protons and neutrons surrounded by a cloud of electrons. The proton count fixes which element it is.
- What is the most abundant element in the universe?
- Hydrogen, which makes up roughly 75 percent of ordinary matter by mass. Helium is second at about 24 percent.
- What is the most abundant element in Earth's crust?
- Oxygen, about 46 percent by mass, mostly locked into silicate minerals rather than free as a gas.
- What does the formula for water tell you?
- Water is written H2O: two hydrogen atoms bonded to one oxygen atom, with the molecule bent at about 104.5 degrees.
- What orders the elements in the periodic table?
- Atomic number, the number of protons in the nucleus, increasing left to right and top to bottom.
- What is an isotope?
- An atom of the same element with a different number of neutrons, so the same chemistry but a different mass.
- What does the pH scale measure?
- How acidic or basic a solution is, from 0 to 14, with 7 neutral. Each step of 1 is a tenfold change in hydrogen ion concentration.