Idea 2of 11Builds onWhich way is plusStart to finish
A minus sign is a direction
Plus fourteen and minus twenty: what is minus six?
Today you'll discover
- why minus twenty is not a smaller twenty
- what a minus sign on an answer means on the ground
- how to read −9 m
Think firstTwo moves: plus fourteen, then minus twenty
Is minus twenty metres a shorter move than plus fourteen metres?
Decide first, then press Next. Watch where the heavy arrow ends: left of the ring it began at.
Arrows over a metre scale, built up by pressing Next. First the bare line with a ring at the start and the key that east is plus, west minus. Then a warm arrow fourteen to the right, labelled plus fourteen. Then a cool arrow from its head twenty back to the left, past the ring, labelled minus twenty. Then the heavy lower arrow from the ring six to the left, labelled minus six. The last step shows one arrow labelled minus nine and asks what it means.
See the whole ideathe big idea and the key word, in one place
The big idea
The number says how much. The sign says which way.
Easy to get wrongA negative velocity is not a slowing down. It is motion the other way, as fast as the number says.
Key word
- negative
- pointing against the direction chosen as positive; the sign is the direction, written as algebra
Ready to use it?
- Turn a signed answer back into a direction in brackets.