What is the difference between speed and velocity?

speed is the rate of change in distance thus it is scalar physical quantity

while velocity is the rate of change in displacement thus it is a vector physical quantity

Explanation:

vector physical quantity: is a quantity that requires both magnitude and direction to identify

scalar quantity: requires only magnitude to identify.

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .

heat the gas and measure the pressure