# Force to turn a generator

• 01-01-2014, 06:36 PM
abdo799
Force to turn a generator
A total newbie here , please bear my ignorance.
If I had a moving body and i wanted to generate electricity from this movement , I figured out how to connect it to a generator so when i moves the generator's shaft turns . Now i need to know if the speed of the body will be the same if i didn't connect it to the generator , for example , the force on the body is 5000 N and it's mass is 50 Kg , it will have an acceleration of 100m/s^2 , will this acceleration be the same if it was connected to the generator ( about how it's connected , the body has gear teeth integrated to a drive chain ( like the one in the bicycle) turning gears and turning the generator) , also what will be the efficiency of this generator , will it be like the water turbine ( over 90%)?. Thanks
• 01-01-2014, 11:34 PM
Timelord
Simple physics
Ignoring how it is connected, any "power" (Watts) produced by the generator will subtract from the "power" (Force x Distance / Time) accelerating the mass, thus it will accelerate at some lower rate or stop as the case may be. Is this a steady state problem?
Chain drive is a quite efficient way to change mechanical advantage, bicycle chains approach 98%. Plus you have to consider the efficiency of the generator and any bearing losses.

Timelord
• 01-02-2014, 04:11 AM
abdo799
[QUOTE=Timelord;8204]Ignoring how it is connected, any "power" (Watts) produced by the generator will subtract from the "power" (Force x Distance / Time) accelerating the mass, thus it will accelerate at some lower rate or stop as the case may be. Is this a steady state problem?
Chain drive is a quite efficient way to change mechanical advantage, bicycle chains approach 98%. Plus you have to consider the efficiency of the generator and any bearing losses.

Timelord[/QUOTE]

How to calculate the decrease in acceleration , if the generator has 50% efficiency will the body go 50% slower? If it have 100% it wont move?
• 01-02-2014, 04:31 AM
abdo799
Basically, i have a body that produces 1000 W kinetic energy , how much can i extract from the moving body as electricity ?
• 01-02-2014, 05:53 AM
abdo799
[QUOTE=Timelord;8204]Ignoring how it is connected, any "power" (Watts) produced by the generator will subtract from the "power" (Force x Distance / Time) accelerating the mass, thus it will accelerate at some lower rate or stop as the case may be. Is this a steady state problem?
Chain drive is a quite efficient way to change mechanical advantage, bicycle chains approach 98%. Plus you have to consider the efficiency of the generator and any bearing losses.

Timelord[/QUOTE]
How could it stop anyway? the force acting on it is like gravity , always constant and never stops acting on the body
• 01-02-2014, 05:32 PM
Timelord
[FONT=Calibri][SIZE=3][COLOR=#000000] [QUOTE]How to calculate the decrease in acceleration , if the generator has 50% efficiency will the body go 50% slower? If it have 100% it wont move?[/QUOTE]
[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The efficiency of the generator does not equate in any way to the reduction in [U]acceleration[/U]. The problem has a lot to do with how you extract the work.[/COLOR][/SIZE][/FONT]
[FONT=Calibri][SIZE=3][COLOR=#000000][QUOTE]Basically, i have a body that produces 1000 W kinetic energy , how much can i extract from the moving body as electricity ?[/QUOTE]
[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]Watts are a measure of power, not energy. How do you produce the power?[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]You have given very little data about the application. You tell us it is a linear force being used to accelerate a mass and you want to bleed off some of the work being done to drive a generator. Then you tell us that the connection is by chain, which typically used to transmit rotary motion. Generators are typically rotary devices, but could be a linear device. Due to the lack of information, I gave a generic conservation of energy answer that applied only to what you said. If you want more help, explain what you are trying to do. It sounds to me like you need to engage the services of a mechanical engineer as this is very basic physics and mechanics.[/COLOR][/SIZE][/FONT]

[FONT=Calibri][SIZE=3][COLOR=#000000]Timelord[/COLOR][/SIZE][/FONT] ..........................................................................................
• 01-02-2014, 06:18 PM
abdo799
I can make a simple sketch of what i meant and attach it to a reply , would that help?
• 01-03-2014, 01:08 PM
abdo799
[QUOTE=Timelord;8215][FONT=Calibri][SIZE=3][COLOR=#000000]
[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]The efficiency of the generator does not equate in any way to the reduction in [U]acceleration[/U]. The problem has a lot to do with how you extract the work.[/COLOR][/SIZE][/FONT]
[FONT=Calibri][SIZE=3][COLOR=#000000]
[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]Watts are a measure of power, not energy. How do you produce the power?[/COLOR][/SIZE][/FONT] [FONT=Calibri][SIZE=3][COLOR=#000000]You have given very little data about the application. You tell us it is a linear force being used to accelerate a mass and you want to bleed off some of the work being done to drive a generator. Then you tell us that the connection is by chain, which typically used to transmit rotary motion. Generators are typically rotary devices, but could be a linear device. Due to the lack of information, I gave a generic conservation of energy answer that applied only to what you said. If you want more help, explain what you are trying to do. It sounds to me like you need to engage the services of a mechanical engineer as this is very basic physics and mechanics.[/COLOR][/SIZE][/FONT]

[FONT=Calibri][SIZE=3][COLOR=#000000]Timelord[/COLOR][/SIZE][/FONT] ..........................................................................................[/QUOTE]

[ATTACH=CONFIG]901[/ATTACH]

question 1:
How to calculate the decrease in the acceleration of the body if the generator was connected ?
question 2:
consider this case:
if the distance between the 2 gears was large enough so the body reached terminal velocity , will the generator still produce electricity?

I hope that was clear enough
• 01-03-2014, 11:32 PM
Timelord
[FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT][FONT=Calibri][SIZE=3][COLOR=#000000]You originally stated the problem as a force of 5000N accelerating a mass of 50 kg. Your sketch is now something entirely different. It is shown as a mass “falling” in a standard gravity.[/COLOR][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT][FONT=Calibri][COLOR=#000000][SIZE=3]OK, about the sketch, any power produced by the generator requires a torque supplied by tension on the belt/chain shown in the sketch. This tension is in direct opposition to the “falling” weight direction. So work backwards from the power you expect from the generator to the resulting tension in the belt/chain which will oppose the apparent weight of the object. Gravity is a constant 32 ft/sec[/SIZE][SUP][SIZE=2]2 [/SIZE][/SUP][SIZE=3]for most practical distances, and in this case only enters into converting the mass to a tension force. [/SIZE][/COLOR][/FONT] [FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT][FONT=Calibri][SIZE=3][COLOR=#000000]Again even with a sketch, you have given very little information about your actual problem. I have to ask. Is this a theoretical homework problem? This is very basic physics & mechanics.[/COLOR][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT][FONT=Calibri][SIZE=3][COLOR=#000000]Timelord [/COLOR][/SIZE][/FONT] [FONT=Times New Roman][SIZE=3][COLOR=#000000] [/COLOR][/SIZE][/FONT]