Q 01/05

Which everyday sight is plasma, the fourth state of matter?

A) Lightning

B) Chimney smoke

C) Morning fog

D) Steam

Answer · why

A) Lightning

Lightning is plasma: in a split second the bolt heats the air in its path to around 30,000 °C, and that air's explosive expansion is the thunder.

Q 02/05

Particles in a liquid stay close but slide past each other, so a liquid keeps what?

A) Its shape but not its volume

B) Its volume but not its shape

C) Both shape and volume

D) Neither shape nor volume

Answer · why

B) Its volume but not its shape

Its volume but not its shape: with no container at all, a small falling raindrop is not a teardrop but a tiny ball, and bigger ones flatten like a bur...

Q 03/05

Which property of water lets a water strider walk across a pond without sinking?

A) Surface tension

B) Buoyancy

C) Viscosity

D) Capillary action

Answer · why

A) Surface tension

Surface tension: water molecules cling to one another so strongly that the top layer acts like a stretched skin, and the insect's long legs spread its...

Q 04/05

Propane is a gas at room temperature, so what keeps it liquid inside a barbecue tank?

A) High pressure

B) Extreme cold

C) A chemical additive

D) A vacuum

Answer · why

A) High pressure

High pressure holds the propane as a liquid; open the valve and, as the pressure falls, it boils back into the gas that feeds the flame.

Q 05/05

What does plasma contain that an ordinary gas lacks?

A) Free-moving charged particles

B) Free-floating neutrons

C) Short-lived antimatter

D) Unusually heavy atoms

Answer · why

A) Free-moving charged particles

Free-moving charged particles make a plasma respond to magnets, which lets fusion researchers confine it with magnetic fields and heat it hotter than ...