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本文介绍笔者在运动生物力学教学中，利用投影器进行“人体在腾空状态下角动量守恒，肌力不能改变整体角运动量及重心在空间的位置”和“动态支撑反作用力产生机理”的力学实验方法及原理。第一项实验主要是以一个有髋横轴的人体模具置于投影器上，以橡筋代替体前或体后肌群，使模具由伸至层或由届至伸，形成上体与腿同时绕髋横轴相向转动的动态投影。由于投影器玻璃平台和模具都光滑，摩擦力可忽略；模具重力在水平面上无分力，对模具在水平面内的运动不起作用，创设了人体腾空状态下的力条件，并演示了在该条件下角动量守恒，内力不能改变总角动量，也不能改变重心空间位置的力学规律。第二项实验是将一条小绳拉直，两端固定于投影器上，充当地面硝人体模具的脚轻靠小绳，并先使成屈体或直体姿势依靠橡筋作动力，使模具由层至仲或由伸至屈，即可看到相当于人体挺身跳起或屈体下降的动态投影。因模具脚端受小绳约束，当模具在内力作用下，上体与腿同时绕髋横轴作相向转动时，对小绳的压力改变，小绳的反作用力也就随之改变，生动形象地演示了动态支撑反作用力产生的机理。
This article describes the author in the teaching of sports biomechanics, the use of projectors to “human body in the state of vacated momentum conservation, muscle strength can not change the overall angular momentum and the location of the center of gravity” and “dynamic support reaction mechanism of mechanics,” the mechanics of experimental methods And the principle. The first experiment is based on a human body with a horizontal axis of the hip projector placed on the projector to replace the rubber band before or after the body muscles so that the mold by stretching to the layer or by extension to form the upper body and legs at the same time Dynamic projection around the horizontal axis of the hip rotation. As the projector glass platform and the mold are smooth, friction can be neglected; mold gravity in the horizontal plane without force, the mold in the horizontal plane movement does not work, created the human body vacated state of force conditions, and demonstrated in the Under the conditions of conservation of angular momentum, internal forces can not change the total angular momentum, nor change the mechanical laws of the location of the center of gravity space. The second experiment is to straighten a small rope, fixed at both ends of the projector, as the ground nitrate human foot lightly rely on small rope, and first make the ponchos or straight body posture rely on rubber as the motivation to make the mold From the layer to the middle or by stretching to the flexion, you can see the equivalent of human body to rise or pike drop dynamic projection. Due to the restraint of the foot of the mold by the small rope, when the mold is under internal force, the upper body and the leg rotate around the horizontal axis of the hip at the same time, the pressure on the small rope changes and the reaction force of the small rope changes accordingly. Demonstrates the mechanism of dynamically supporting reaction forces.