Doors and Energy

Doors and Energy

I work in an office building.  As part of my job, I am required to travel through the building often to see people.  I have to go through a lot of (secured) doors.

This brings up some questions.

At the entrance to the building:

Does it use more of my energy, to go through a heavy revolving door, or to pull open 2 heavy entrance doors (one after another)?

If someone has gone through the door ahead of me, and the door is closing slowly, does it use more of my energy, to pull that same door open again, or to pull open (for myself) the closed door that is next to it?  (I am pulling against the closing inertia, or pulling from zero.)

At the building elevator:

The elevator is run by a motor.  The motor coils or uncoils a cable, which makes the elevator go up or down.  The motor goes at the same speed, all the time.

Does it take more power, to lift more people, than if the car is empty?  Since the elevator motor still has to run to lower the car, again, does it take less power to lower a full elevator?

If the answer is no, because the motor just runs, no matter how much weight is in the car, shouldn’t we all be bringing some extra weight up with us?  This weight would then become Potential energy, which we could release somewhere, and create motion, which becomes Kinetic energy.

From Wikipedia, the free encyclopedia:

Potential energy can be thought of as energy stored within a physical system. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy, and to do work in the process. The standard (SI) unit of measure for potential energy is the joule, the same as for work or energy in general.

Potential energy is energy that is stored within a system. It exists when there is a force that tends to pull an object back towards some original position when the object is displaced. This force is often called a restoring force. …. when a weight is lifted up, the force of gravity will try to bring it back down to its original position. The initial steps of … lifting the weight both require energy to perform. According to the principle of conservation of energy, energy cannot be created or destroyed; hence this energy cannot disappear. Instead, it is stored as potential energy. If … the weight is dropped, this stored energy will be converted into kinetic energy by the restoring force — … gravity in the case of the weight.

http://en.wikipedia.org/wiki/Potential_energy

Or, are we losing energy through the elevator motor, in BOTH directions?  Seems like somebody should do something about that.  I’d say we’re throwing away a great deal of potential energy.

Anyway, back to doors.

If I go through a door, and someone is following a few steps behind me, it is normal for me to hold the door a few extra seconds for them, so they don’t have to open it.  Everyone does this.  As I said, it’s normal.

Do I need to be thanked for this?  Think about it.

If I didn’t hold the door, I would be a jerk.  So you are thanking me, for not being a jerk.  I don’t need that.

Of course, if I go out of my way, and open the door, but let you go through FIRST, or, hold the door open for you, for more than a few seconds, then I think it is reasonable to expect a small thank you.

If you have a burden, or are pushing a cart, no thanks are needed.  I’ll take a few extra seconds, and go out of my way, to help you. I would expect you to do the same for me.  If I didn’t, again, I would be a jerk.  A standard greeting is sufficient.

Good day.  And, thank you.  For not being a jerk.