Aflea walking along a ruler moves from the 45 cm mark to the 27 cm mark. it does this in 3 seconds. what is the speed? what is the velocity?
(define increasing numbers to be the positive direction and decreasing numbers to be the negative direction.)

Explanation:

In the calculation of distance we do not take into account the direction of movement .So only magnitude of movement is taken care of.

On the other hand , in respect of displacement , we take into account even direction of movement along with magnitude.

Distance covered by flea = 45 - 27 = 18 cm

Displacement by flea = 27 - 45 = - 18 cm

Speed = Distance covered / time

= 18 / 3 = 6 cm / s

Velocity = - 18 / 3 = - 6 cm /s.

that tool is called an altimeter which measures your altitude which can be used to tell which atmosphere you are currently in, including the stratosphere.

hope this ! : )

3. dark matter

empty space could also be a simple vacuum