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We have in LO.5 Physics G10
First: the Concepts
A. Center of mass
B. Torque
C. Static equilibrium
D. Translational vs. Rotational Equilibrium
E. The equilibrium torque condition: rotational analogue of Newton's Laws
F. Simple machines
G. The mechanical advantage of simple machines
H. Stability of extended rigid bodies depends on the sum of the forces, the sum of the torques and on the location of the centre of mass.
Second: the References
Third: the Videos links
Fourth: Skills
A. Determine the centre of mass for different objects and systems of objects
B. Calculate the magnitude of the total torque acting on an object
C. Identify forces and torques acting on a stationary extended object, and be able to apply the equilibrium torque condition.
D. Determine the torque of a simple machine: the lever.
Fifth: the materials as PPT., DOCX., and PDF
In the Drive from this link
Few Notes:
What is torque?
Torque is a measure of the force that can cause an object to rotate about an axis. Just as force is what causes an object to accelerate in linear kinematics, torque is what causes an object to acquire angular acceleration.
Torque is a vector quantity. The direction of the torque vector depends on the direction of the force on the axis.
Anyone who has ever opened a door has an intuitive understanding of torque. When a person opens a door, they push on the side of the door farthest from the hinges. Pushing on the side closest to the hinges requires considerably more force. Although the work done is the same in both cases (the larger force would be applied over a smaller distance) people generally prefer to apply less force, hence the usual location of the door handle.
Figure 1: Opening a door with maximum torque.
Torque can be either static or dynamic.
A static torque is one which does not produce an angular acceleration. Someone pushing on a closed door is applying a static torque to the door because the door is not rotating about its hinges, despite the force applied. Someone pedaling a bicycle at constant speed is also applying a static torque because they are not accelerating.
The drive shaft in a racing car accelerating from the start line is carrying a dynamic torque because it must be producing an angular acceleration of the wheels given that the car is accelerating along the track.
The terminology used when describing torque can be confusing. Engineers sometimes use the term moment, or moment of force interchangeably with torque. The radius at which the force acts is sometimes called the moment arm.
How is torque calculated?
The magnitude of the torque vector tau for a torque produced by a given force F is
where r is the length of the moment arm and theta is the angle between the force vector and the moment arm. In the case of the door shown in Figure 1, the force is at right angles (90degrees) to the moment arm, so the sine term becomes 1 and
tau, equals, F, dot, r.
The direction of the torque vector is found by convention using the right hand grip rule. If a hand is curled around the axis of rotation with the fingers pointing in the direction of the force, then the torque vector points in the direction of the thumb as shown in Figure 2.
Figure 2: Direction of the torque vector found with the right-hand rule.
How is torque measured?
The SI unitfor 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. The magnitude of these units is often similar as 1, space, N, m, \simeq, 1, point, 74, space, f, t, dot, l, b, s.
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. There is a direct equivalent to Newton’s 2ⁿᵈ law of motion (F, equals, m, a),
tau, equals, I, alpha.
Here, alpha is the angular acceleration. I is the rotational inertia, a property of a rotating system which depends on the mass distribution of the system. The larger 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?
The concept of rotational equilibrium is an equivalent to Newton’s 1ˢᵗ law for a rotational system. 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.
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