Q 01/05

Stars are almost pure balls of which state of matter, estimated to be 99.9% of all ordinary matter in the universe?

A) Gas

B) Liquid

C) Plasma

D) Solid

Answer · why

C) Plasma

Plasma is a gas so hot its atoms have been stripped of electrons, which is why it conducts electricity and glows in neon signs and lightning bolts.

Q 02/05

When Apollo 15's David Scott dropped a hammer and a falcon feather side by side on the Moon, what happened?

A) The hammer landed first

B) They landed together

C) The feather landed first

D) The feather never landed

Answer · why

B) They landed together

They landed together because the Moon has almost no atmosphere, so no drag slowed the feather, exactly as Galileo had predicted centuries earlier.

Q 03/05

Lakes freeze from the top down because liquid water is at its densest at roughly what temperature?

A) 0 °C

B) −4 °C

C) −10 °C

D) 4 °C

Answer · why

D) 4 °C

4 °C is where water is heaviest, so the colder water near freezing floats on top and ice forms there first, leaving fish alive underneath all winter.

Q 04/05

An 80 kg astronaut keeps the same mass on the Moon, but their weight there drops to roughly what fraction of Earth's?

A) One sixth

B) One half

C) One tenth

D) One twentieth

Answer · why

A) One sixth

One sixth is the figure because gravity on the Moon is only about 1.6 m/s², so a suited astronaut could bound along despite carrying 80 kg of kit.

Q 05/05

Ice is roughly 10 percent less dense than seawater, so how much of a floating iceberg sits below the waterline?

A) About 50%

B) About 90%

C) About 75%

D) About 99%

Answer · why

B) About 90%

About 90% of an iceberg is hidden underwater, which is why the Titanic's lookouts saw only a small peak and why 'tip of the iceberg' means what it doe...