我们对物体用力,就会感到肌肉紧张。如你用手提水桶、脚蹬自行车、肩背书包或在运动场上拔河、抛球、掷铁饼等活动,你都会感到肌肉紧张。这种紧张,我们就说是用了力,就是对物体施加了力。不但人能对物体施加力,其他物体也能对别的物体施加力。如在工地上你可看到推土机推土时对土施加力;在实验室你可 When we force on an object, we feel nervous. If you use buckets, pedal bikes, shoulder bags, or tug-of-war, tossing, discus throwing, etc., you will feel nervous. With this kind of tension, we say that we use force to exert force on objects. Not only can people exert force on objects, other objects can also exert force on other objects. If on the construction site you can see that the bulldozer pushes the soil when it pushes the soil, in the laboratory you can