If you had said the make and type I would have told you why. -As is , the problem is either the belt, the wigwag, the pump, a loose pipe or the transmission. -Call an appliance repairman is your best way to fix it.
Centrifugal Force.
Yes, a washing machine transitions from one cycle to another. There is a water cycle that transitions to a wash cycle, then it transitions to a rinse cycle, a spin cycle and so on.
Centrifugal force created in the spin cycle forces the water out of the clothing.
A washing machine begins a wash cycle with clean tap water. If, at the end, the water discharged after the final spin is not full of dirt, then the soap and washing machine has not cleansed the clothes!
because it is
I buy a new one
When you washing machine is in the spin cycle the agitator should rotate along with the drum of your washing machine and that's normal. There is no way it could be going up and down and will only appear that is is agitating while on spin.
In a modern washing machine, the wash, rinse and spin cycles are controlled by special purpose (embedded) computers.
The spinning cycle works on a centrifuge mechanism
Your washing machine is still running but no more spin wash or jerking it only spins still in the middle and it does not squeeze out the water well like before what should you fix it?
I would suggest that you take it to a repair person specialized in washing machines.
Not all.