[Physics Class Notes] on Difference Between Torque and Power Pdf for Exam

Intuition plays an important role in physics for learning mechanics.

If you have a strong intuition, it becomes easy for you to assimilate things.

If you are studying rotational mechanics, it becomes necessary for you to groom up your intuitive ability to understand things.

That’s why rotational mechanics is one of the toughest topics in mechanics.

Let’s understand the concept of torque interactively by using our intuition.

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If we apply a force on the fans of a fan, it starts rotating, however, on applying a force at its center, it remains unmoved. 

This is because no translational motion occurs at the center.

This center is the fixed point of a fan. On drawing a line through this point, we get an axis that keeps the fan rotating in a plane perpendicular to it.

So, this axis is the axis of rotation.

Let’s Consider Two Cases Here

Case 1: On applying a force towards the center, this force will pass through the axis, and no force will act on it.

Since the distance between the force F, and the distance ‘d’, is zero. That’s why the fan remains unmoved.

Case 2: Now, if we apply a force of the fans of this fan, the force won’t pass through the axis, because force F is at a distance ‘d’, from the axis of rotation.

Here, the rotation will occur.

So, the force acts at a perpendicular distance ‘d’, from the axis of rotation of the fan.

What is Torque?

The product of the force and the perpendicular distance is the ‘torque’. It is denoted by a Greek letter, tau, or て. Its formula is:

て = F x d

So, in case 1, The product, て is zero because the perpendicular distance between the axis and the force applied is zero.

In case 2, on applying a force at a distance ‘d’, from the axis, we got て = F x d; however, the magnitude of the force is the same in both the cases.

It means that the only application of force won’t rotate the fan; rather torque is responsible for its rotational motion.

Difference Between Torque and Power

Torque and horsepower are both ways of measuring force.

Torque measures force and power measures work i.e., force overtime.

We can imagine torque as a twisting or whirling force. So, if we apply a force on a body at some distance from its axis of rotation, a twisting force or torque supplied to make it rotate.

The same happens with a socket wrench while tightening down a bolt. We apply a force at a distance, and that supplies torque to that bolt to fasten down it.

Let’s consider a toolbox and one meter-long wrench, and if we fasten a bolt by applying one Newton of force, it means that we are applying one Newton-meter torque on it

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The same thing happens with the engine of our car.

Engine torque measures the amount of the force that an engine produces.

Let’s consider a piston, driving the crankshaft; we can see that where it is attached, turns around its axis just like the wrenches turned around the bolt.

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The combustion within the cylinder supplies the force in pressing down the piston, pushes the crankshaft.

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The force exerted on the crankpin is transferred to the shaft to get it spinning.

How is the Torque Determined?

The torque is determined by two factors, i.e: Torque = The product of the amount of force on the crankpin which comes from the piston, and the distance of that force from the center axis, or throws which vary by the crankshaft.

If the throw remains the same, we generate more force from the piston which means more displacement.

We can increase torque if the force from the piston remains the same. Therefore, we can increase the distance of the pin from the crankshaft center to increase the torque.

Difference Between Torque and Power in Cars

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Let’s consider a car moving at a certain speed ‘s’. If it moves at a high speed, it means an enormous force is supplied to make it move faster, which means fastly, the wheels are spinning.

Well, fastly the car moves, the more revolutions wheels make while spinning. So, horsepower is the torque multiplied by rpm (revolutions per minute) or the rate of work done.

So, how fast a wheel spins is the point where we get consistent with the force acting on the piston.

The faster the shaft spins by applying the same force at the same distance, the more power it will make. 

Let’s Understand this by an Example

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Car A has 300 Horsepower and has 100 N-m of torque.

Car B has 100 hp and 300 N-m of torque, which is 1/3 rd of the power and thrice the torque as that of in car B.

So, car A has more hp i.e, thrice to that of car B, and ⅓ of torque.

Which means car A moves faster as it has high acceleration.