力是一个向量;它有方向和幅度。力的SI单位是牛顿（N）。一个力的牛顿等于1 kg * m / s2，其中“*”符号代表“时间”。力也由符号F.牛顿的第一运动定律表示，除非被外力作用，否则物体将继续以恒定速度移动。运动中的物体保持运动，直到力作用于它们。这是惯性。他们不会加速，减速或改变方向，直到某些事情发生在他们身上。力与加速度成比例，加速度定义为速度的变化率。在微积分方面，力是动量相对于时间的导数。力量的概念最初由艾萨克·牛顿爵士在他的三个运动定律中定义。他将重力解释为拥有质量的身体之间的吸引力。然而，爱因斯坦广义相对论中的引力并不需要力。牛顿第二运动定律表明，力与恒定质量的加速度（动量变化率）成正比。同时，加速度与质量成反比。该定律对测量力非常有用。如果您知道其中两个因素，则可以计算第三个因素。你也知道，如果一个物体正在加速，必须有一个力作用于它。牛顿第三运动定律涉及两个物体之间的相互作用。它说，对于每一个动作，都有一个相同而相反的反应。当力施加到一个物体时，它对产生力但在相反方向上的物体具有相同的效果。动作和反作用力同时发生。如果你拉绳子，绳子会拉回来。
Force is a vector; it has both direction and magnitude. The SI unit for force is the newton (N). One newton of force is equal to 1 kg * m/s2, where the “*” symbol stands for “times.” Force is also represented by the symbol F. Newton’s First Law of Motion says that an object will continue to move at a constant velocity unless it is acted upon by an external force. Objects in motion remain in motion until a force acts on them. This is inertia. They won’t speed up, slow down, or change direction until something acts on them. Force is proportional to acceleration, which is defined as the rate of change of velocity. In calculus terms, force is the derivative of momentum with respect to time. The concept of force was originally defined by Sir Isaac Newton in his three laws of motion. He explained gravity as an attractive force between bodies that possessed mass. However, gravity within Einstein’s general relativity doesn’t require force. Newton’s Second Law of Motion says that force is directly proportional to acceleration (the rate of change of momentum) for a constant mass. Meanwhile, acceleration is inversely proportional to mass. This law is useful for measuring forces. If you know two of the factors, you can calculate the third. You also know that if an object is accelerating, there must be a force acting on it. Newton’s Third Law of Motion relates to interactions between two objects. It says that for every action there is an equal and opposite reaction. When a force is applied to one object, it has the same effect on the object that produced the force but in the opposite direction. The action and reaction forces happen at the same time. If you pull on a rope, the rope is pulling back on you.