See this answer for a more detailed explanation of the geometry in mechanics. I believe that your question is best answered by the gyroscope experiments. First, the gyroscope not spinning, is supported on both ends. One support is then removed, and the gyro "falls. This motion is perpendicular to both, the gravity force vector and the torque vector. This proves that torque generates a vector that is perpendicular to the plane of rotation. Physicists often say they use first principles thinking, but in order to come up with those first principles, they always use real world observations and create equation s to explain the observation, but sometimes cannot explain the fundamental reason behind the observation which gave rise to the equation.
In three dimensional space, there are two possible orthogonal vectors torque vector in this example relative to another plane rotating object in this example. The torque vector could potentially be in either direction, thus it's counterintutitive. Our universe from what humans observe from Earth and outer space in our solar system just so happens to use the right hand grip rule for the direction of the torque vector. It just is. It might be coincidental that we have other phenomena using this right hand grip rule in the "Interesting Facts" below.
It's how the universe was designed. It was simply using an analogy they observe on Earth with spinning objects. The first video below explains it very well. The T is simply what they measure torque for the spin procession of each effect. Physicists have not proven why the torque vector points in the direction of the thumb when using the right hand grip rule. They simply show a value with units based on the math. See second video on how the right hand grip rule works.
Video 3 shows a lot more of the mathematics. Just make sure to use the correct units Newton meters for the torque for physics when solving an equation. Take a look here for conversion units if using foot pounds.
If the force vector and the torque vector apply to the same direction as the right hand grip rule, you get a positive torque vector, because there really is a perpendicular force torque. If it's the opposite direction, you get a negative torque vector. But in reality, the forces are in both directions in physics, since you always have equilibrium with Newton's Third Law. But in mathematics, you need to show which one is positive and which one is negative for the first principles to work out.
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Create a free Team What is Teams? Learn more. Why does torque point perpendicular to direction of the motion? Ask Question. Asked 4 years, 7 months ago. Active 1 year, 1 month ago. Viewed 14k times. Improve this question. There is no "logical" reason for using the right hand vs left hand vs big toe, but making the vector be the axis of rotation vs, say, making it a tangent to some circle around the axis, or simply representing it as a scalar allows the axis to be identified as a part of the vector, vs needing a separate quantity.
Add a comment. Active Oldest Votes. Improve this answer. The motion of flying objects is described by this third type of motion; a combination of translation and rotation.
A force F is a vector quantity , which means that it has both a magnitude and a direction associated with it. The direction of the force is important because the resulting motion of the object is in the same direction as the force. A torque is also a vector quantity and produces a rotation in the same way that a force produces a translation. Namely, an object at rest, or rotating at a constant angular velocity, will continue to do so until it is subject to an external torque.
A torque produces a change in angular velocity which is called an angular acceleration. The distance L used to determine the torque T is the distance from the pivot p to the force, but measured perpendicular to the direction of the force. On the figure, we show four examples of torques to illustrate the basic principles governing torques. In each example a blue weight W is acting on a red bar, which is called an arm.
In Example 1, the force weight is applied perpendicular to the arm. In this case, the perpendicular distance is the length of the bar and the torque is equal to the product of the length and the force. In Example 2, the same force is applied to the arm, but the force now acts right through the pivot. In this case, the distance from the pivot perpendicular to the force is zero. So, in this case, the torque is also zero. The torque "vector" direction defines the axis of the motion that it tends to induce, and for the same reason that torque as a vector is a bit of a trick, even the notion of axis only works in two and three dimensions.
Torque is about rotation, and rotations primarily are about transformations that are confined to planes. When we do higher dimensional geometry, rotations change planes and leave more than one dimension invariant. So, in general, the easiest way to specify a rotation is by specifying the plane that it changes , rather than specifying the subspace that it leaves invariant.
It just so happens that in three dimensions, the subspace left invariant is a line or an "axis"- so the two approaches amount to the same thing. We can define a plane in three dimensions by specifying a vector normal to it, which is why we can get away with a torque or angular velocity as a vector. In general these quantities are directed planes, not lines with direction. How can the bolt turn clockwise if the force is concentrated perpendicular to where it needs to turn?
Because that force is perpendicular to the direction towards the rotation-centre. Not to the turning direction. The bolt does indeed turn in the same way as the force pulls it. When you define a torque vector direction , you have a problem. You can't define a vector direction as something that turns around. The direction must be along a straight line.
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