Question

the blood in veins flow slower than the blood in the arteries. Why?

Answer 1

because the veins are small and they required little blood so I hope this is your answer

Answer 2

The answer is pretty simple… remember, (almost) all the pressure in the blood vessels is created when the heart pumps out the blood during systole. The arteries divide and divide, until they reach the levels of the capillaries, where the exchange of nutrients (ie glucose, oxygen, etc) are exchanged for tissue waste products (carbon dioxide, urea, etc). These vessels are not stiff tubes - some of the pressure is “absorbed” by the flexible blood vessels, so the further the distance from the heart, the less the pressure becomes. In addition, these big vessels literally split into millions of these tiny vessels, so the pressure in these tiny vessels is quite low. Coming out the “out” side, these vessels containing waste products converge into the relatively low pressure veins - most of the pressure has already been absorbed/dissipated by the artery walls and evened out by the process of splitting into the capillaries.

I hope this answers the question okay for you!