Newton's 3 Laws of Motion

Newton’s Laws of Motion

In the late 1600’s, Isaac Newton described the relationship between the forces exerted on an object and its motion using three physical laws, known collectively as Newton’s laws of motion. Newton’s first law, often referred to as the principle of inertia, states that an object’s motion will remain constant unless it is acted on by an unbalanced force. This means that an object at rest will remain at rest, and an object in motion will maintain a constant velocity unless an unbalanced force changes its motion. Inertia refers to the tendency of objects to resist a change in their motion. It depends on an object’s mass; the greater the mass, the more inertia it has and the harder it is to change the motion of the object.

Newton’s second law describes how the net force affects the motion of an object. It states that the net force exerted on an object is a product of its mass and its acceleration; in other words, net force equals mass times acceleration (F=ma). Further, it states that the object will accelerate in the same direction as the net force. Newton’s second law can help us understand the relationship between mass and weight. The force that Earth’s gravity exerts on an object is called weight; weight is a force. The object’s mass, the amount of matter contained within it, is a physical property of that object. So, weight is the effect that gravity has on mass; they are not synonyms.

Newton’s third law, often called the action-reaction law, says that when one object exerts a force on another object, then the second object exerts an equal but opposite force on the first. In other words, for every action there is an equal but opposite reaction. As you are sitting in your chair reading this, your weight is exerting a downward force on the chair. You may feel the pressure on your back-side where your body is coming into contact with the chair. The pressure you feel is because the chair is exerting an equal but opposite upward force on your bottom. As long as these two forces balance, you will remain seated. However, if your weight is stronger than the upward force the chair is capable of providing, you will crush the chair and accelerate downward!

NEWTON'S LAWS OF MOTION