Here's what OpenAI's CHATGPT4 says:
Horsepower takes into account both the engine's torque and its rotational speed, so it reflects how fast the engine can produce the torque. In simpler terms, horsepower is what keeps a car moving at high speeds, once it's already in motion.
It's not how fast the engine CAN produce torque, it's how quickly the engine IS producing torque. Torque is the force required to induce movement of an object at rest. Horsepower is
how quickly that torque is being applied.
In general, as rpms go up, both torque and horsepower increase until they reach the top of their respective output curves.
As the horsepower goes up with rpms, it produces the corresponding rpm torque more quickly as the rpms increase.
A car with high torque will have good acceleration and towing capability, while a car with high horsepower will have a higher top speed.
A lousy, even incorrect, generalization. Acceleration is a function of horsepower and gearing, NOT torque. And high horsepower doesn't guarantee "higher top speed", that's a function of the final gear ratio and aerodynamics with any given engine and bodywork, nothing else. All you get is quicker acceleration.
Take the case of diesel engines: The reason they're the default engine for heavy hauling is that they develop very high torque at very low rpms.
You don't normally want to get a 10-20,000 lb trailer moving with a quick jerk off the line, you want a steady gradual no-wheelspin controllable pull. Nobody drag races diesels, they have tractor pulls. Although Audi won the 24 hours of LeMans with a turbo-diesel few years back, the cars were geared especially for racing and in fact it was the fuel economy allowing fewer pit stops that edged out the win in the end, not simply a "faster car".
You notice that the consumption is kind of inverse of ICE-car - less in city traffic - more on highway.
This is where
inertia comes in: The Newtonian rule of physics that an object in motion tends to stay in motion until acted on by an outside force. That's why ICE's are more efficient at freeway cruising speeds.
Electric motors produce 100% of their torque across their entire rpm range. Since there are no transmissions, vehicle speed is a direct 1-1 correlation to motor rpm.
So when that motor is turning higher rpms to deliver higher speeds, it's using as much electricity as required to get that rpm. One can't 'coast" with an electric car. If one lifts off the throttle, regenerative braking kicks in, and all the energy used getting to speed is immediately turned to battery-stored energy and wasted heat, but the energy recovered from braking can never equal or exceed the energy used to attain a given speed in the first place.
In a gas vehicle, once I get to the desired speed, inertia keeps the car moving and far less energy input from the engine is needed to maintain a steady speed. Using the transmission, a higher gear may then be selected which allows the engine to turn more slowly and use less gas, while still producing "just enough" power to maintain speed.
With an electric motor it's
all or nothing and how fast do you want it? You're gonna use more power to go and keep going faster because it's generating 100% output all the time no matter what the rpms are.
In a sense, electric motors could be said to be "digital" in that they're either on or off, and ICE's are good old analog where everything happens on the continuum of a curve.
Maybe this is a better analogy:
One can't simulate a dimmer switch by trying to flip a 100-watt bulb on and off rapidly. It's always at 100% when it's on.
A dimmer switch allows voltage reduction so there's less lumens output,
continuously.