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Torque is the force required to rotate an object around an axis. Just as force causes an object to accelerate in linear kinematics, the torque also causes an object to acquire angular acceleration. It is also referred to as the moment, moment of force, rotational force, or turning effect, depending on the field of study. Torque is a vector quantity.
Check also: Class 11 Physics Chapter 7 System of Particles and Rotational Motion
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What is Torque?
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- Torque is the force that can cause an object to rotate along an axis.
- Torque is also responsible for angular acceleration.
- As a result, torque can be defined as the rotational equivalent of a linear force.
- The point at which the item rotates is known as the axis of rotation.
- Torque is the tendency of the force to turn or twist the object.
- Torque is described using a variety of terminologies, including moment and moment of force.
- The twisting force that creates motion is referred to as torque.
- The product of the amount of the force acting on the particle and the perpendicular distance of the force applied from the object’s axis of rotation is the torque operating on the object.
- Newton-Meter (N·M) is the SI unit for torque.
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Torque in our Everyday Life
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When we hear the word 'torque,' it's almost always in the context of automobiles. Torque is a term that is frequently used to describe a car's power, but what precisely does it mean? Torque is the force exerted by pistons on the crankshaft, which causes it and the wheels to turn in a car.
Torque is a broad physics term that has various applications, despite its association with automobiles. The axis of rotation is the point at which the object is rotating. You use torque on a daily basis without even recognising it. When you just open a locked door, you apply torque three times. The key is turned, the doorknob is turned and the door is pushed to open.
Examples of Torque
In Seesaw many people have observed someone sitting on one end of a seesaw while the other sits on the other end, with one person being heavier than the other. Because the moment arm of a heavier person is shorter than that of the lighter person, the heavier person can reduce torque by sitting closer to the pivot. Because the lever arm is smaller, the torque is reduced, allowing lighter people to lift bigger objects.
Formula of Torque
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Torque is the multiplication product of the radius vector (from the axis of the rotation to the site of force application) and the force vector. The Torque is represented by symbol τ.
| τ = F x r x Sin(θ) |
Here,
F → linear force
r → distance between the axis of rotation and the point at which linear force is applied.
θ → angle between the r and F.
Torque Types
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Torque is of two types Static and Dynamic torque.
Static Torque: The torque that does not cause an angular acceleration is known as static torque. When a person pushes a closed door, static torque is applied because the door does not rotate despite the force applied.
Dynamic Torque: The drive shaft of a racing car accelerating from the start line carries the dynamic torque since it must produce an angular acceleration of the wheels if the car is accelerating along the circuit.
Torque Determination by Thumb Rule
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The right-hand thumb rule is used to determine the direction of the torque vector. The torque vector points in the direction of the thumb if a hand is wrapped around the axis of rotation with the fingers pointing in the force direction.
- Turn your right hand in the direction of the position vector (r and d), then your fingers in the direction of the force, and your thumb in the direction of the torque.
- The direction is reversed when either the direction of r or the direction of F is reversed. If the direction of both r and F is reversed, the direction of torque will remain unchanged. The torque is defined here in terms of a certain point, commonly referred to as the origin. When the same force is applied to a different origin, the torque is different. As a result, determining the source is critical.
- If the force vector is 0o or 180o, the force will not affect the axis rotation. It would either be shoving away from the axis of rotation or shoving towards the axis of rotation because it is in the same direction. In both of these circumstances, the torque value is zero.
- Perpendicular to the position vector, the most influential force vectors for producing torque are θ = 90o or –90o. This is because it will have the greatest impact on increasing rotation.
How is Horsepower linked with Torque?
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Before purchasing a vehicle, we frequently hear people discussing horsepower and torque, particularly when it comes to racing cars. A horsepower is a unit of power measurement that represents the pace at which work is completed.
The term "horsepower" refers to the engine's total power output. To put it another way, if torque is the force that pushes you back in your seat during acceleration, horsepower is the speed reached at the end of that acceleration.
Horsepower is calculated by multiplying torque by rpm and dividing by a constant. Now that there is a limit to how quickly a vehicle's engine can spin, having more torque allows for more horsepower at lower rpm (revolutions per minute).
Rotational Equilibrium
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For a rotational system, the concept of rotational equilibrium is comparable to Newton's first law. An object that is not rotating stays that way unless it is acted on by an external torque. Similarly, until acted on by an external torque, an object revolving at constant angular velocity will continue to revolve.
When dealing with difficulties involving several torques acting on a rotating item, the idea of rotational equilibrium comes in handy. In this scenario, it's the net torque that matters. If a rotatable object's net torque is zero, it will be in rotational equilibrium and unable to gain angular acceleration.
What is Torque in a Car?
Torque represents a rotational or twisting force. The engines in vehicles rotate about an axis creating torque. It can be considered as the strength of a vehicle. Torque is what rockets a sports car from 0-60 kmph in seconds. Torque is also what powers big trucks hauling heavy loads into motion.
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Things to Remember
- Torque is also known as a moment of force.
- The rotating equivalent of linear motion mass (inertia) is known as the moment of inertia.
- Formula of torque is τ = F x r x Sin(θ).
- Torque is the twisting force applied by the crankshaft, which is a measure of a vehicle's ability to perform work.
- Horsepower refers to how quickly a vehicle can complete a task.
- The product of torque and revolutions per minute is horsepower.
- Because there is a limit to how rapidly an engine can spin, having more torque allows for more horsepower to be produced at lower rpm.
Sample Questions
Ques: What is the difference between Torque and Force? (2 marks)
Ans: In rotational mechanics, torque is the opposite of force. Torque is the ability of a force to generate a twist around an axis, which is the main difference between them.
Ques: Is the car getting faster due to Torque? (2 marks)
Ans: The product of torque and revolutions per minute is horsepower. Basically, the more power an engine produces, the faster the crankshaft rotates with the same amount of force. An automobile with greater horsepower than torque will always be faster, as this provides acceleration and speed.
Ques: What are the day to day life examples of torque? (2 marks)
Ans: Opening the door and opening the bottle cap are some of the day to day life examples of torque.
Ques: Where does torque play a role? (2 marks)
Ans: A crescent wrench releasing a lug nut, a playground seesaw, a doorknob, opening a Coke bottle, and even in-car engines and steering wheels are all examples of torque in action.
Ques: What is the definition of torque in the human body? (2 marks)
Ans: The force that propels humans ahead is called torque. Controlling the torque of the target muscle will provide a more accurate intervention. The moment arm of a force system is the perpendicular distance between an axis and the line of action of a force. The force exerted by muscles through a moment arm of a certain length and at a specific angle to the joint is known as muscular torque.
Ques: Are torque in the electric medium and the magnetic medium the same? (2 marks)
Ans: No, Torque in an electric medium refers to the force generated in an electric field, while torque in a magnetic medium refers to the force felt in a magnetic field.
Ques: Torques of equal magnitude are applied to a hollow cylinder and a solid sphere, both having the same mass and radius. The cylinder is free to rotate about its standard axis of symmetry, and the sphere is free to rotate about an axis passing through its centre. Which of the two will acquire a greater angular speed after a given time? (3 marks)
Ans: Let M be the mass and R the radius of the hollow cylinder, and also of the solid sphere. Their moments of inertia about the respective axes are I1 = MR2 and I2 = 2/5 MR2
Let τ be the magnitude of the torque applied to the cylinder and the sphere, producing angular accelerations α1and α2 respectively. Then τ=I1 α1 = I2 α2
The angular acceleration 04 produced in the sphere is larger. Hence, the sphere will acquire a larger angular speed after a given time.
Ques. Explain why friction is necessary to make the disc roll in a specific direction.
(a) Give the direction of frictional force at B, and the sense of frictional torque, before perfect rolling begins.
(b) What is the force of friction after perfect rolling begins? (3 marks)
Ans: To roll a disc, we require a torque, which can be provided only by a tangential force. As the force of friction is the only tangential force, in this case, it is necessary.
- As frictional force at B opposes the velocity of point B, which is to the left, the frictional force must be to the right. The sense of frictional torque will be perpendicular to the plane of the disc and outwards.
- As frictional force at B decreases the velocity of the point of contact B with the surface, the perfect rolling begins only when the velocity of point B becomes zero. Also, the force of friction would become zero at this stage.
Ques. A merry-go-round, made of a ring-like platform of radius R and mass M, is revolving with angular speed ω. A person of mass M is standing on it. At one instant, the person jumps off the round, radially away from the centre of the round (as seen from the round). The speed of the round afterwards is? (3 marks)
Ans: As no torque is exerted by the person jumping, radially away from the centre of the round (as seen from the round), let the total moment of inertia of the system is 2I (round + Person (because the total mass is 2M) and the round is revolving with angular speed ωSince the angular momentum of the person when it jumps off the round is Iω the actual momentum of round seen from ground is 2 Iω – Iω = Iω
So we conclude that the angular speed remains the same, i.e ω
Ques. What is the difference between torque in an electric medium and torque in a magnetic medium? (3 marks)
Ans: Torque is referred to as the product of force as well as the perpendicular distance between the point of application of force and the pivot point. Torque in an electric medium defines the force experienced in an electric field. Similarly, torque in a magnetic medium is the force experienced in a magnetic field.
Ques. How does torque differ from force? (2 marks)
Ans: Torque is a counterpart of force in rotational mechanics. The major difference between them is that torque is the ability of a force to produce a twist around an axis.
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