Torque is a Force applied to cause rotation.
1 ft-lb of torque is equal to one pound of force applied 1 foot from the center of rotation and is equal to 12 in-lbs (inch pounds)
1HP = 1 lbft of torque applied at 5252 rpm for 1 minute.
Any measure of power requires a force x velocity over a unit of time.
Torque is converted to force when it is tranformed from rotary motion to linear motion through the use of gearboxes and tractive devices (tires) -
F=ma is a basic newtonian physics relationship, and (F)orce is derived directly from (T)orque through the gearbox and tires. (m)[censored] is how much your truck weighs and (a)cceleration is basically what you are after.
The longer you can apply acceleration, the faster you will go and the faster you go, the more horsepower you require to overcome drag and friction.
Trucks that haul stuff benefit from having low end torque for accelerating heavy loads from a dead stop. Race cars benefit from having torque at higher speeds where the engine will spend most of its time. A big truck with a 500 HP motor rated at 1800 rpm max would be able to move 40 tons easily while a race car rated at 500 HP at 6000 rpm may not even be able to budge the load.
HP is the work to keep a vehicle going at speed.
Torque is the neccesary force to get it going in the first place.
