Flow rate depends on:

• Potential difference

• Area (size of “pipe”)

• Permeability (or “roughness”)

High potential

Same high potential

Lower potential

Water flows from high potential to low potential

A high flow rate generates lots of power

In a water pipe:“Conductance” is proportional to AREA x PERMEABILITY

• Area (size of “pipe”)

• Permeability (if the water must flow around sand or gravel in the pipe)

The opposite of Conductance is “RESISTANCE”

In an electric wire or light bulb:“Conductance” is proportional to AREA x CONDUCTIVIY

• Area (size of “wire” or “filament”)

• Conductivity (the current must flow around atoms in the wire)

The opposite of Conductance is “RESISTANCE”

Imagine water flowing in a “loop” or “circuit”

Imagine water flowing in a “loop” or “circuit”

Imagine water flowing in a “loop” or “circuit”

Imagine water flowing in a “loop” or “circuit”

Units:

• “Fluid potential” is measured in the same units as “pressure”

• The SI unit of pressure is the Pascal or “Pa”

• Pascals are tiny so we often usekilopascals or “kPa”

Units:

• A useful unit for work and energyis the joule.

• One joule is about ¼ calorie.

• One joule is also the energy neededto move one liter of water through apotential difference of one kPa.

Units:

• Power is “energy per unit time”

• Power is measured in watts

• 1 watt = 1 joule per second

Units:

• 1 watt = 1 joule per second

• Lighting a 40 watt bulb for 10 seconds consumes 400 joulesof energy

• 1 kWhr = (1 kW)(3600 s) = 3.6 million joules

Electrical Units:

• The stuff that flows is called CHARGE• The unit of charge is the COULOMB

• The flow of charge is called CURRENT• The unit of current is the AMP

Electrical Units:

• The unit of potential is the VOLT• A potential difference is called VOLTAGE

Electrical Units:

• The unit of energy is the JOULE• Energy is determined by • The amount of charge that moves• The change in potential of each charge

Electrical Units:

• The unit of power is the WATT• Power is determined by • The rate of motion of charge (CURRENT)• The change in potential of each charge