BBC Knowledge June 2017

PHOTOS: GETTY X4, REUTERS

Are fireworks bad for the environment?

Fireworks propel a cocktail of chemicals into the atmosphere, many of which

can harm both people and the environment. The vivid colours in firework displays

come from metallic compounds such as barium or aluminium that can have negative

impacts on animal and human health. Additionally, to produce the oxygen needed

for an explosion, many fireworks contain oxidisers known as perchlorates.

These can dissolve in water, contaminating rivers, lakes and drinking water.

Finally, fireworks release a fine cloud of smoke and particulate matter, affecting local

air quality. Some newer, ‘cleaner’ fireworks replace perchlorates with safer alternatives,

or use compressed air to reduce the smoke created.

Sucking a thumb or dummy up to the age of

two is fine, but several studies have shown

that, beyond that, there is a risk that the front

teeth can be pushed outward, or the side teeth

shifted so that the top and bottom sets don’t

meet. A 2001 study by the American Dental

Association found that about 20 per cent of

children who suck their thumb beyond the age

of four have a misaligned bite. LV

Does sucking your

thumb really ruin

your teeth?

Multiple explanations have been proposed. We may forget because we didn’t store the memory
effectively in the first place. It is also possible that memories decay over time. As they have
not been revisited, their biological ‘trace’ becomes weak. Another theory suggests that
new memories can interfere with older ones. Or that memories have been encoded and stored
but that there is a problem with retrieval. Scientists sometimes refer to ‘motivated forgetting’ too,
which involves forgetting an unwanted memory such as a trauma. This is controversial as
there is also evidence that such unwanted events may be particularly difficult to forget.
Forgetting is not always a bad thing! It would waste cognitive resources if we remembered
every last detail of the world around us. AGr

Why are fats solid

at room temperature

but oils liquid?

To form a solid, molecules need to pack

together nicely, while, in a liquid, there is less

order and the molecules flow around each

other. Fat molecules are mostly made up

of long, straight hydrocarbon chains.

Because they are straight, they pack neatly

with their neighbours (think of the way

uncooked spaghetti packs together in a jar).

Oils generally have chains that are kinked;

this stops them interacting so tidily and so

they stay liquid (imagine the storage problems

you’d have if there was a bend in the middle

of every piece of spaghetti). By definition, fatty

molecules that form liquids are called oils and

those that form solids are called fats. ML

Why do we forget things?

| & ANSWERS

QUESTIONS

20 June 2017