[niky]

Originally Posted by sendler

True. My point exactly. In all gears those lines will all show the same power at the wheel as the engine is sending out even though the torque is much higher in the lower gears, the wheel speed is much lower. It's a wash. The power at the wheel is the same in any gear.

No. The force at the wheels is different due to the gearing. Power to the wheels is force applied over time, which is shown in the second graph. Perhaps it's better understood as acceleration in "gravities"... which is always greatest in the lowest gear (barring traction issues), which indicates that more work is being done.

Yes. the acceleration inlower gears is always much greater than the higher gears because the speed is much lower. Hence, the energy of the vehicle is much lower. So any new energy that is added from the engine power is a big change. At faster speeds the energy of the vehicle can be 20 times, ect, what it was at the slower speed. But you are still only adding more energy from the same engine output 1 unit at a time. Now each time you look at it, you have increased the energy of the vehicle only 5%.

Speed is inconsequential. If you can exert the same amount of accelerative force at high speeds as at low speeds, you can give the same acceleration rate. See the example, again, of rockets, which have linear acceleration because they don't rely on gearboxes to translate engine rotation into motive force. It is only because we use driven wheels to move cars that acceleration tapers off.

Look at the dyno of the trucks again. They are modern turbo diesels and they do have a very weird, ultra flat power band. At any identical wheel speed where the gears have an rpm that is on the power band, say 3rd is 3,500, 4th is 3,000 and 5th is 2,500, The acceleration would be exactly the same. The gearing can't transform the power it is given. It only transforms the wheel speed to the engine speed.

Again, the dyno is meaningless in this context, because you're using it incorrectly. It's an extrapolation based on wheel torque. And altering the ratio of wheel speed to engine speed DOES alter the acceleration potential of the engine. Which means it DOES have an effect on work done. Even on cars with a totally flat torque curve, acceleration is always fastest in the lowest gear.

I do get what you're trying to say. If a motor makes x hp at y speed, it should have z acceleration, regardless of gearing or rpm. However, the dyno you cite doesn't show that. And only electric motors can make constant power over wide spreads, which is why most electric cars can do without a gearbox.

I'm not using horsepower per second. I am using horsepower times seconds. Which is energy. The same as a Watt hour or a Joule. Momentum is just one of many forms of energy.

You're describing momentum. You have to use the units for momentum. Have you ever tried multiplying horsepower by time? I made that mistake when building the Excel calculator that generated the first sheet. It spat out gibberish. Pro-tip, don't ever try to calculate wheel-horsepower by running engine output through a gear-ratio conversion.

Horsepower is torque/time. Horsepower x time is equal to (torque x time)/time. Which, by process of cancellation, is torque.

Originally Posted by mort

This is nonsense. It takes power to accelerate in space just like on earth. If your engine produces 100 hp and your rocket mass is 600 lb your acceleration at 100 mph will be .625 g. At 1000 mph acceleration will be .0625 g

-mort

Your acceleration rate would stay the same until relativistic effects increase the mass enough to blunt accelerative force. There is no drag in space, so acceleration will not taper off.

Actually, that's slightly wrong. As the rocket accelerates, it's using up propulsion mass... which makes it lighter... which makes it accelerate faster.

As seen here:

The acceleration change for the first stage is more dramatic because it's leaving the gravity well. The final stage is more indicative of how a rocket will accelerate in flat space, with acceleration increasing slightly every second that reaction mass is consumed.

A rocket with infinite fuel or, even better, a ramscoop, will show up on that graph as a flat line. It accelerates at a constant rate given constant thrust output.

It doesn't matter what speed you're going. Applying force x in one direction causes x acceleration in the other, along any vector, no matter what your velocity is on the other vectors.

This is because a rocket doesn't use propellant to push against the space behind it. It pushes on the propellant itself. Which makes the actual speed of the rocket inconsequential, much like a hypothetical infinite treadmill under the wheels of an airplane at take-off.

Besides, as the entire Milky Way is moving at 135,000 miles per hour towards the great attractor, a difference of just 900 mph in the rocket's relative velocity is just a drop in the bucket.