cog

Everyday

1. A cog is one of the teeth around the edge of a wheel in a machine; a whole wheel with teeth is also called a cog or cogwheel (gear). tree →
2. (figurative) «A cog in the machine» is a person who has a small part in a big organisation and feels unimportant. tree →
3. (UK, slang) In some places, «to cog» means to copy someone's homework. tree →

In the lessons

In science and DT lessons, cogs (gears) show how turning one wheel can turn another faster, slower or the other way; a small cog turning a big cog makes it turn more slowly but with more force. In stories, «the cogs were turning» means someone was thinking hard. Phrases: «a cog in the machine», «cogs turning», «cogwheel».

Examples

• The clock's cogs turned slowly behind the glass. tree →
• When the big cog turns once, the small cog turns three times. tree →
• A missing tooth on the cog jammed the machine. tree →
• You could see the cogs turning in his head as he worked out the puzzle. tree →
• He felt like a tiny cog in a huge company. tree →
• We built a cog model from cardboard and pins. tree →
• The bike's chain runs over cogs at the back wheel. tree →

Note

Countable noun: one cog, two cogs. In maths problems with gears, if a big cog has 30 teeth and a small one 10, the small cog turns 3 times for each turn of the big one (30 ÷ 10 = 3).