Elementary Definitions
1) Work
Is the ‘physical effort’ required to do some thing, such as pulling a Bucket of Water out of a Well. Its measure or ‘Unit’ is ‘foot-pounds’ or ‘kg-meters’. As an example, consider pulling a bucketful of water weighing 15 Kgs from a depth of, say, 10 Meters. So the ‘work’ done is 15 x 10 = 150 ‘kg-meters’.
2) Power
It’s the ‘Rate’ of doing ‘Work’, such as pulling 10 buckets as above in one hour or a part of it.
The most popular unit of Power is the ‘Horse Power’, which from ancient times was the rate of work an ‘average horse’ could do. In scientific parlance today, it translates into 4,500 kg-m/min or 33,000 ft-pounds/min. In Metric System of Measurement, therefore, one ‘horsepower’ = 746 Watts.
In post-war Germany, ‘PS’ was and is still used – which was/is a functional equivalent of the ‘British’ Horse Power. In reality, it equates as 1.0 HP = 1.07 PS. Today, it seems the Car/Advertisers use ‘PS’ atleast in India to mislead the gullible public - as the same HP/BHP ‘sounds’ a little higher when expressed in PS!
3) Energy
It’s defined as ‘the Capacity’ of doing work, such as lifting a 10kg weight up to a height of 5 Meters and then ‘giving up’. Or like a Tank full of a Car that can take you, say, 500km before it needs to be filled up again. It’s measure, therefore, is ‘kg-meters’ or Watt-hours etc. A ‘KW/Kilo-Watt’ is simply = 1000 Watts.
4) Torque
While most of us can imagine that ‘Force’ is a ‘linear’ thing – like 2-people applying ‘X’ amount of force to ‘push’ a Car weighing ‘Y’ kgs, when it comes to ‘Torue’, most people find it difficult to comprehend as to what it is.
In other words, it can be defined as the force required to ‘twist or turn’ some thing, For example, like kicking down the starting lever of a Mobike, which actually ‘rotates’ the Bike’s engine to get it going. The measuring ‘Unit’ of such a ‘rotary-force’, therefore, is ‘kg-meters’ or ‘Foot-Pounds’ as its FPS equivalent (not to be confused with the unit of work).
Here, ‘kg’ is the ‘linear or tangential force’ applied to the kick pedal – say ‘F’ and ‘meter’ being the ‘radial length’ of the kick-starting lever – say ‘R’. Therefore, the ‘torque’ applied in this instance to the kick-pedal shaft, to rotate the engine, is ‘F x R’ kg-meters.
Suffice to say that all ‘rotating’ machines like Engines/Elect. Motors etc., essentially produce a ‘rotary force’ at their 'output shaft’. Since they also
‘rotate’ over a designed range of ‘speeds’ – RPM in their case - they inevitably have a ‘Speed vs Torque Characteristic’ when the two variables/Torque and RPM are plotted on an X-Y axis.
Since by definition ‘Power’ is the ‘rate’ of doing work, in case of a Rotating machine or an ICE, Power is simply a straight ‘multiple’ of ‘torque’ and ‘rpm’ - at that particular ‘rpm’. It follows, therefore, that the ‘shape’ of the ‘Power vs Rpm’ Curve of an ICE is quite similar to that of its ‘mother’ Torque vs Rpm’ Curve.
Practical difference between Torque and Power
We have thus seen that ‘Torque’ is the prime ‘driving force’ that is produced by an Engine and in its units of measurement, there is no ‘time factor’. It’s the Torque, therefore, that’s transmitted to a Vehicle’s drive wheels via its Gearbox. Further, it’s capable of being ‘multiplied’ by its Gearbox Ratios.
In other words, if an Engine is producing ‘X’ amount of Torque at its Flywheel and the net gear ratio between it and the drive wheels is 1:Y, then the torque available at the drive wheels would be ‘X x Y’ Units/Kg-Meters. And if the Wheel radius is, say’, 0.5 Meters, then the ‘linear’ force available at the wheels circumference and the road will be X x Y/0.5 or = 2 x X x Y Kgs.
To sum-up presently, it’s the Torque capability of an Engine that determines its ‘Acceleration’ abilities.
On the other hand, ‘Power’ is a multiple of the Engine Torque AND its ‘Rpm’ – the latter having a ‘Time’ factor in it. It, therefore, follows that the ultimate speed that a vehicle can achieve in any gear is a function of the ‘Power output’ capabilities of an Engine – coz ‘Speed’ has ‘time’ element in it too.
thank you all for your input i deffo want to paint mine in met black pearl now . think it will look great!!!