GM College Physics Torque Concepts
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The SI unit for torque is the Newton-meter. In imperial units, the Foot-pound is often used. This is confusing because colloquially the pound is sometimes used as a unit of mass and sometimes force. What is meant here is pound-force , the force due to earth gravity on a one-pound object. Measuring a static torque in a non-rotating system is usually quite easy, and done by measuring a force.
Given the length of the moment arm, the torque can be found directly. Measuring torque in a rotating system is considerably more difficult.
One method works by measuring strain within the metal of a drive shaft which is transmitting torque and sending this information wirelessly. What role does torque play in rotational kinematics? In rotational kinematics, torque takes the place of force in linear kinematics. I I I is the rotational inertia , a property of a rotating system which depends on the mass distribution of the system.
The larger I I I , the harder it is for an object to acquire angular acceleration. We derive this expression in our article on rotational inertia. What is rotational equilibrium? An object which is not rotating remains not rotating unless acted on by an external torque. Similarly, an object rotating at constant angular velocity remains rotating unless acted on by an external torque. The concept of rotational equilibrium is particularly useful in problems involving multiple torques acting on a rotatable object. In this case it is the net torque which is important.
If the net torque on a rotatable object is zero then it will be in rotational equilibrium and not able to acquire angular acceleration. Consider the wheel shown in Figure 3, acted on by two forces. A wheel acted on by two torques.
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Note that here we are defining positive torque in the direction out of the page. We know that in rotational equilibrium. How does torque relate to power and energy? There is considerable confusion between torque, power and energy.
More on moment of inertia. The concept of rotational equilibrium is particularly useful in problems involving multiple torques acting on a rotatable object. The radius at which the force acts is sometimes called the moment arm. So it's Let me do it in a brighter color. Breaking down the load of concepts into small pieces allows me to see exactly where I am understanding, or not understanding, the concepts. Although it has less height than the previous one.
For example, the torque of an engine is sometimes incorrectly described as its 'turning power'. Torque and energy have the same dimensions i.
What is torque?
They differ in that torque is a vector quantity defined only for a rotatable system. Power however, can be calculated from torque if the rotational speed is known. In fact, the horsepower of an engine is not typically measured directly, but calculated from measured torque and rotational speed. Along with horsepower , the peak torque produced by a vehicle engine is an important and commonly quoted specification. Practically speaking, peak torque is relevant for generally describing how quickly a vehicle will accelerate and its ability to pull a load.
Horsepower relative to weight on the other hand is more relevant to the maximum speed of a vehicle. The maximum speed of a vehicle occurs when the power developed by the engine becomes equal to the rate of work done by friction and drag. See our article on power for more detail on this. It is important to recognize that while maximum torque and horsepower are useful general specifications, they are of limited use when making calculations involving the overall motion of a vehicle. This is because in practice both vary as a function of rotational speed. The general relationship can be non-linear and differs for different types of motor as shown in Figure 4.
In steam engines and electric motors the rate of conversion of energy from the primary source steam from a boiler, electricity from a battery is mostly independent of the rotational speed. In internal combustion engines the combustion pressure and temperature increase with rotational speed. An optimum combination of these variables occurs at a specific rotational speed, leading to the observed peak in available torque. Relationship of available torque to rotational speed for different sources.
How can we increase or decrease torque? It is often necessary to increase or decrease the torque produced by a motor to suit different applications.
Recall that the length of a lever can increase or decrease the force on an object at the expense of the distance through which the lever must be pushed. Similarly, the torque produced by a motor can be increased or decreased through the use of gearing. An increase in torque comes with a proportional decrease in rotational speed. The meshing of two gear teeth can be viewed as equivalent to the interaction of a pair of levers as shown in Figure 5.
The meshing of two gears viewed as the interaction of two levers. The use of adjustable gearing is necessary to obtain good performance in vehicles powered by combustion engines.
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These engines produce maximum torque only for a narrow range of high rotational speeds. Adjustable gearing allows sufficient torque to be delivered to the wheels at any given rotational speed of the engine. Bicycles require gearing because of the inability of humans to pedal with a cadance sufficient to achieve a useful speed when driving a wheel directly unless one is cycling a penny-farthing.
The old-style penny-farthing type bicycle used a large front drive wheel up to 1. A Penny-Farthing type bicycle.
Torque and equilibrium
Adjustable gearing is not typically required in vehicles powered by steam engines or electric motors. In both cases, high torque is available at low speeds and is relatively constant over a wide range of speeds. The winch drum has a radius of 0. Product details File Size: August 26, Sold by: Share your thoughts with other customers. Write a customer review. Amazon Giveaway allows you to run promotional giveaways in order to create buzz, reward your audience, and attract new followers and customers.
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GM College Physics Torque Concepts - Kindle edition by DR. N. N. MATHEW, DR. GEORGE MATHEW. Download it once and read it on your Kindle device, PC . COLLEGE PHYSICS TORQUE CONCEPTS IS a masterpiece creation. Once again, Dr. George Mathew takes the complex subject of college physics torque.
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