As the water in cup B gets deeper, it pushes harder and harder on your finger. The flow stops when the level of water is the same in both cups and there is no difference in pressure. There is a water current only while there is a difference of pressure on the 2 ends of the straw. Similarly, an electric current flows only if there is a difference of electrical pressure between 2 places, which causes electrons to move from one place to the other. The unit measuring potential difference is the volt .
Kids Can Press.
For kids ages 9 to 12. For kids ages 9 to 12. All rights reserved.