AA battery to lift 1000kg up 1meter

[one_q_a_day]

I am on the Earth's surface and I want to lift my 1000kg rock up 1m.

I quickly calculate the amount of work required to accomplish this feat:

1000kg * 9.81 m/s² * 1m = 9800 kg m²/s² or 9800 joules

thats really not that much work.

i see from http://www.allaboutbatteries.com/Energy-tables.html" that the energy stored in a single long-life alkaline AA battery is 9360 joules. almost what i need to lift the rock by one meter.

it seems incredulous to me to think that one AA battery could be used to lift a 1000kg rock up one meter. what a i missing?

 

[tamtam402]

A second battery.

 

[russ_watters]

You're not missing anything - as long as you gear down your winch so it takes 5-10 min to expend its energy, it should work. (but add a second battery for safety factor). There isn't as much potential energy in lifting a weight as most people think...or maybe its vice versa.

 

[sophiecentaur]

There is also a small matter of efficiency, which may be relevant in this particular system because such a low gear ratio is involved. You'd probably really need the second battery - or even more - in practice.
But it goes to show what good value mechanical energy is in 'making a difference' to situations compared with thermal energy. 9800J would only raise the temperature of a cup of water by a few degrees.

 

[Cleonis]

[...] it goes to show what good value mechanical energy is in 'making a difference' to situations compared with thermal energy. 9800J would only raise the temperature of a cup of water by a few degrees.

This brings back a memory.
On a bicycle it's a backbreaking effort to climb a mountain that is 1 kilometer high. Just for the heck of it I calculated how much water could be brought to a boil with the same amount of energy. I had a hard time believing the result; it gave me a whole new respect for my stove's ability to bring a whole kettle of water to the boil in minutes.

 

[sophiecentaur]

I may be too nerdy but things like that make me pleased I have been an engineer!

 

[russ_watters]

Meh, I do that kind of thing all the time. My friends give me funny looks when I pull factoids like that out of my...the air...but they are things I get curious about.

Ever calculate how much it costs to make ice in your freezer? If you ever considered turning off the ice maker to conserve energy, you never will again.

 

[Cleonis]

Ever calculate how much it costs to make ice in your freezer?

I think there's a catch here.

When I'm heating water on a stove then the change of temperature comes from a conversion process: potential chemical energy is converted to heat.

However, in the case of a freezer the change of temperature is effected by transporting heat. Heat is withdrawn from the water in the freezer, and dumped outside the freezer. It is my understanding that the energy cost of heat transportation is less than the cost of conversion.

This means that a simple calculation just looking at the amount of Joules of energy involved in freezing/thawing may well give a higher number than the actual energy consumption of the freezer.

 

[mrspeedybob]

Meh, I do that kind of thing all the time. My friends give me funny looks when I pull factoids like that out of my...the air...but they are things I get curious about.

Ever calculate how much it costs to make ice in your freezer? If you ever considered turning off the ice maker to conserve energy, you never will again.

You have to include both the cost of operating the ice-maker and the cost of additional heat load on your homes AC system, of course in the winter the second cost is actually a credit. Did you include these factors in your calculation?

 

[Barwick]

it seems incredulous to me to think that one AA battery could be used to lift a 1000kg rock up one meter. what a i missing?

A rather long time for the entire process to happen. If the battery isn't rechargeable, you also have to determine the amount of "work" that is being done by the battery just to support the 1000kg while it's lifting for say 20 minutes at 9.8m/s^2 * 1000kg.

Though it's not technically work, it's energy that's being expended.

 

[russ_watters]

A rather long time for the entire process to happen. If the battery isn't rechargeable, you also have to determine the amount of "work" that is being done by the battery just to support the 1000kg while it's lifting for say 20 minutes at 9.8m/s^2 * 1000kg.

Though it's not technically work, it's energy that's being expended.

As the commercial says: it's in there. That force is the lifting force.

 

[MagnetDave]

It's just a lot of practical considerations. You need to produce a certain voltage to make a practical motor produce enough torque to really lift the load. The battery is limited to 1.5V. You are not going to be 100% efficient extracting that energy, and not close to 100% turning it into work. In theory, it should be possible, but I would be surprised if it were anywhere close to practical.

 

[sophiecentaur]

A rather long time for the entire process to happen. If the battery isn't rechargeable, you also have to determine the amount of "work" that is being done by the battery just to support the 1000kg while it's lifting for say 20 minutes at 9.8m/s^2 * 1000kg.

Though it's not technically work, it's energy that's being expended.

The only extra energy expended would be to overcome friction. Your "keeping it up" is a bit of a red herring. If the mass is moving then the force from the motor will be bigger for that reason. The friction in the sort of gearbox necessary for this task (I.e. very low gear) would be enough to prevent the load going down even if the motor were turned off for a while. Practical worm drives can't be made to work the other way round, for instance.