Power and Torque

[flawless101]

Hiya,

 

Could someone explain the difference between power and torque?

Is it also correct to say that how much torque a car has determines its acceleration and how much power it has determines its top speed?

 

flawless101

[ajb]

Power is the rate of change of work. Work is the amount of energy transferred by a force acting through a distance. For a rigid body, like a car work can be understood as the change in kinetic energy. Thus the work is a "measure" of the change in velocity, taking the mass to be constant.

 

Torque or moment of a force is the "tendency of the force to rotate an object about an axis".

 

Have a look at the wikipedia entry on machine torque. I think it will address your questions better than I can.

[insane_alien]

High Torque means high acceleration. This is simply because more torque means more force available for acceleration and by applying a=F/m increasing the force means higher acceleration.

 

of course this is potentially countered by using different sized wheels, nbut assuming all other parameters are the same does indeed mean more acceleration.

 

High power can mean a higher top speed (as you can counter more drag) however top speed also depends on the torque. having all the power you need to counter drag at 800mph is useless if you do not have the torque to counter the drag force.

 

this is why it's hard to get wheel driven cars to go really really fast, your torque is limited by the friction of the tyres(if the torque applied is greater you get wheel spin) so you have a limited amount of force to counter drag with. aero dynamics can come into play here and force you can into the ground more but this both increases drag and ncreases the power required to keep going. eventually this would fall below the breakeven point and you'd be unable to deliver the required force to keep acceleraing(although you'd run into material engineering issues long before then)