Is it power, or is it energy?
What's a Watt?
The differences between power and energy are a great mystery to a lot of folks, and we answer this question a lot. I'll try to do this again for those out there still confused.
Work:
Work (energy) = force x distance
Let's say I have a door on my house that's 1 meter from the hinges to the door knob. If I have to apply 50 newtons of force to the door knob to open the door, and I rotate the door so that the knob moves 1 meter along the arc, I've applied 50 Newton-meters (Joules) of work, or energy.
Power:
Power (Watts) = Work (Joules) / Time (second)
Energy (Watt-hours) = Power (Watts) * time (hours)
Power is Work divided by Time. If I take 1 second to open that door, I've expended (50 joules / 1 sec) = 50 Watts of power. If I take 2 seconds to complete the task, I've expended (50 joules / 2 seconds) = 25 Watts of Power, even though I've still applied 50 Joules of Work.
If I have a 50 watt lightbulb, and I keep it lit for 1 hour, it uses 50 watt-hours. If lit for 2 hours, it uses 100 watt-hours, even though it's a 50 watt bulb and it takes 50 Watts to light it at rated brightness. So, Watt-hours = Power (Watts) * Time (hours), and is a measurement of energy. 100 Wh = 100 Joules/second * 3600 seconds = 360,000 Joules.
Torque:
Torque = Force x Distance
Torque is a force applied to an object that causes a turning motion. In the above example, the door turns on its hinges, the axis of rotation, and since we applied 50 newtons of force to the door handle, and the handle was 1 meter from the axls of rotation, it also happens to be 50 newton-meters of torque. If the doorknob was at the midpoint of the door instead of the edge, or .5 meters from the hinges, I'd have to apply 100 newtons of force to open the door, but that would still be 50 newton-meters of torque.
Conversions:
The above examples were done in metric, and some parts of the world still use English standards, so for ease of understanding, I'll give the conversion units.
50 Joule = 36.8781088 foot pounds
50 Newton = 11.2404471 pounds
1 meter = 3.2808399 feet
1 kilowatt-hour = 3.6 million joules
For more conversions, see http://www.onlineconversion.com/.
The differences between power and energy are a great mystery to a lot of folks, and we answer this question a lot. I'll try to do this again for those out there still confused.
Work:
Work (energy) = force x distance
Let's say I have a door on my house that's 1 meter from the hinges to the door knob. If I have to apply 50 newtons of force to the door knob to open the door, and I rotate the door so that the knob moves 1 meter along the arc, I've applied 50 Newton-meters (Joules) of work, or energy.
Power:
Power (Watts) = Work (Joules) / Time (second)
Energy (Watt-hours) = Power (Watts) * time (hours)
Power is Work divided by Time. If I take 1 second to open that door, I've expended (50 joules / 1 sec) = 50 Watts of power. If I take 2 seconds to complete the task, I've expended (50 joules / 2 seconds) = 25 Watts of Power, even though I've still applied 50 Joules of Work.
If I have a 50 watt lightbulb, and I keep it lit for 1 hour, it uses 50 watt-hours. If lit for 2 hours, it uses 100 watt-hours, even though it's a 50 watt bulb and it takes 50 Watts to light it at rated brightness. So, Watt-hours = Power (Watts) * Time (hours), and is a measurement of energy. 100 Wh = 100 Joules/second * 3600 seconds = 360,000 Joules.
Torque:
Torque = Force x Distance
Torque is a force applied to an object that causes a turning motion. In the above example, the door turns on its hinges, the axis of rotation, and since we applied 50 newtons of force to the door handle, and the handle was 1 meter from the axls of rotation, it also happens to be 50 newton-meters of torque. If the doorknob was at the midpoint of the door instead of the edge, or .5 meters from the hinges, I'd have to apply 100 newtons of force to open the door, but that would still be 50 newton-meters of torque.
Conversions:
The above examples were done in metric, and some parts of the world still use English standards, so for ease of understanding, I'll give the conversion units.
50 Joule = 36.8781088 foot pounds
50 Newton = 11.2404471 pounds
1 meter = 3.2808399 feet
1 kilowatt-hour = 3.6 million joules
For more conversions, see http://www.onlineconversion.com/.
posted by KK4HFJ at
6:01 PM
