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# Energy (Physics) Watch

1. Hi,

I have a few questions regarding energy.

"How does a rotating shaft (on a wind turbine) store energy?"
I did not think that it would store energy. I thought it would be using kinetic energy.

Another question says,
"Different clocks use different energy sources. Describe how a clock can make use of: a) elastic potential energy, b) chemical energy, c) gravitational potential energy?"
A clock could make use of chemical energy by using a battery, but I do not know how it could make use of elastic potential energy or gravitational potential energy.

Any help would be much appreciated!

Thanks
2. (Original post by musicangel)
Hi,

I have a few questions regarding energy.

"How does a rotating shaft (on a wind turbine) store energy?"
I did not think that it would store energy. I thought it would be using kinetic energy.
Hello and welcome to TSR.

You may need to do a bit of googling for yourself but to get you going:

Try a different approach to start with: If a cyclist stops pedalling, would the bicycle stop immediately (assuming no brakes were applied)? Think momentum.

Now think about the wind turbine and what would happen if the wind suddenly stops. Would the shaft stop rotating instantly? How was the energy stored?

(Original post by musicangel)
Another question says,
"Different clocks use different energy sources. Describe how a clock can make use of: a) elastic potential energy, b) chemical energy, c) gravitational potential energy?"
A clock could make use of chemical energy by using a battery, but I do not know how it could make use of elastic potential energy or gravitational potential energy.

Any help would be much appreciated!

Thanks
Have you ever seen an old wind-up alarm clock? How is the energy stored to keep the clock working? Does it go on forever and what do you do to keep it working every day?

Similarly, search out an old cuckoo clock. How does that work? The same principle is used in old grandfater clocks with a pendulum. How does that work? How are they both kept working every day?

http://home.iitk.ac.in/~amit/courses...gar/index.html

http://www.explainthatstuff.com/how-...ocks-work.html
3. (Original post by uberteknik)
Hello and welcome to TSR.

You may need to do a bit of googling for yourself but to get you going:

Try a different approach to start with: If a cyclist stops pedalling, would the bicycle stop immediately (assuming no brakes were applied)? Think momentum.

Now think about the wind turbine and what would happen if the wind suddenly stops. Would the shaft stop rotating instantly? How was the energy stored?
I thought that the only forms of stored energy were gravitational potetial energy and chemical energy. Also, how could momentum be a form of stored energy?

(Original post by uberteknik)
Have you ever seen an old wind-up alarm clock? How is the energy stored to keep the clock working? Does it go on forever and what do you do to keep it working every day?
The clock stored elastic potential energy. To make it work you have to wind up the spring.

(Original post by uberteknik)
Similarly, search out an old cuckoo clock. How does that work? The same principle is used in old grandfater clocks with a pendulum. How does that work? How are they both kept working every day?
A grandfather clock has a pendulum which swings back a forth. When the bob is furthest from the ground, is has the most graviational potential energy. When it moves, the graviational potential energy is converted into kinetic energy. When the bob is furthest from the ground on the other side, the kinetic energy is then converted to gravitational potential energy. To keep the clock working, you have to wind it up
A cuckoo clock has weights that drop over a one day or eight day period and a pendulum. The weights keep the clock working. The first weight and the pendulum make the clock keep the time. The second weight controls the cuckoo. When the weights get near the floor, you have to pull a chain and that puls the weights back to the clock.

4. (Original post by musicangel)
I thought that the only forms of stored energy were gravitational potetial energy and chemical energy. Also, how could momentum be a form of stored energy?
Newton laws of motion. An object will keep moving in straight line or remain stationary unless acted on by an external force.

Also conservation of energy laws: energy can neither be created or destroyed.

Putting the two together, it takes energy to cause an acceleration. But once moving, the object does not require any more energy to keep it moving unless it meets with friction or drag acting in the oppoite direction.

The energy it took to accelerate is stored as kinetic energy by way of its motion. It will keep moving forever unless something else causes it to lose that kinetic energy:

Say it hits a stationary object. Some of the kinetic energy will transer to the object it collided with and some will convert to heat, sound etc. i.e. kinetic energy is most definitely stored energy.

The wind turbine has mass and is rotating so it will store energy as kinetic motion. This is why 'flywheels' with a large mass are often used with rotating mechanical devices so that they keep spinning even when the driving force is removed. Think about a childs spinning top or a gyroscope or the flywheel of a car engine.

Stored energy comes in forms other than gravity and chemical: electric fields, magnetic fields, heat, nuclear energy, tension or compression in a spring etc. are all forms of stored energy.

(Original post by musicangel)
The clock stored elastic potential energy. To make it work you have to wind up the spring.
Yes. The extension of the spring is proportiona to the applied force.

(Original post by musicangel)
A grandfather clock has a pendulum which swings back a forth. When the bob is furthest from the ground, is has the most graviational potential energy. When it moves, the graviational potential energy is converted into kinetic energy. When the bob is furthest from the ground on the other side, the kinetic energy is then converted to gravitational potential energy. To keep the clock working, you have to wind it up
Correct. The gravitational potential is converted to kinetec energy which stores the gpe gained in its momentum. That stored kinteci energy is converted back to gpe as a gain in height of the pendulum on the released as a gain in height.

The spiong of the grandfather clock is their to overcome the forces of friction in the mechanism and with the air. Otherwse the pendulum would stop swinging after a while rather like if you stopped pushing a child on a swing.

(Original post by musicangel)
A cuckoo clock has weights that drop over a one day or eight day period and a pendulum. The weights keep the clock working. The first weight and the pendulum make the clock keep the time. The second weight controls the cuckoo. When the weights get near the floor, you have to pull a chain and that puls the weights back to the clock.

Yes. Again gpe is converted into kinetec energy in the clock mechanism and hands of the clock and also for the cuckoo mechanism.

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