![]() It’s because normal force goes right through the pivot, so the torque it exerts is zero. You may wonder why normal force exerted by the wall is not contributing to rotation. Torque is technically a vector, but for AP® Physics 1&2, you only need to be able to calculate the magnitude of torque and the direction of rotation (clockwise or counterclockwise). Now let’s see what we are really calculating. So then people think of combining these factors together and…Boom, we get the torque equation: To summarize what we discussed earlier, we can find that the effectiveness of turning the wrench is actually related to 3 factors: Force(in example 1), distance from the pivot point (in example 2) and the angle(example 3). ![]() F3 certainly will not contribute to turning the wrench and you may find F2 less efficient than F1 when doing the job. ![]() What about changing the angle of the force exerted on the wrench? As showed in the figure below, F1 is always perpendicular to the wrench while F2 has an angle and F3 is parallel to the wrench. The closer the spot is to the rotation axis, the harder you are likely to turn the wrench. You will find it more effective pushing the wrench at the end than in the middle. If exerted on a different spot, the same force may have different effects. It is easier to turn the wrench when we push it by a greater force. When exerted on the same spot, a greater force is usually more effective than a small force. Still don’t know what a torque is? To understand torque, first, let’s recall a time that you use a wrench to loosen a bolt. Torque is the measure of a force’s effectiveness as making an object accelerate rotationally. Force exerted on this point will not contribute to the rotation. It could be the center of mass or any point that you select. Pivot PointĪ pivot point is a center of rotation. In other words, the center of mass is the point where all the mass of the object could be considered to be concentrated. That certain point is called center of mass. The position of the point varies from pen to pen and are not always in the middle. If you have ever balanced a pen on your finger, you should be very familiar that you could always find a specific point to keep the pen from falling. But how can we be sure? Why does that point summarize and represent the whole object? ![]() In linear motion, we usually treat objects as if they are single particles, and we assume that all the forces are exerted only on a single point that represents the object. To tackle rotation-related questions, we should first expand the moving object from a point to a real object with shape and scale. Basic Elements in Rotation Center of Mass AP® Physics 1 & 2 Crash Course Review will go through all you need to know about rotation and talk about rotation-related questions in AP® Physics and how those equations apply to solve real test questions. In this article, we are going to discuss some basic terms and a set of equations in rotational motion. You may think it’s easy to get confused by those rules, but being analogous to physics of linear motion actually makes the rules of rotational motion very easy to memorize. The object follows many rules while spinning just like the way they do when moving on a straight line. Rotational motion is all about taking an object and spinning it. Speaking of rotational motion, you may think of merry-go-round, a fan or even our rotating earth.
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