Newton's three laws of motion which were written and explained in 1687 are still accepted today. The laws were based upon Galileo's experiments. It has been said that Einstein's Theory of Relativity must modify the laws when speed of an object approaches the speed of light when the distance of something is extraordinarily great. But for everyday mechanical workings Newton's laws apply.
The first law is the law of inertia: an object remains at rest or continues to move at constant speed in a straight line, unless acted upon by some external force. - Let's put this into normal words that are comprehensible.
True inertia can't exist: You throw a stone up in the air and with true inertia it would keep going. Instead, gravity (friction) pulls it down to the ground. The first law suggests that matter (weight) is inertia. The object resists change - that's why it takes a greater force is required to start an airplane than to start a car. Even to stop them, takes more force for a plane than a car. Friction is something that is necessary. It may wear out parts. Think about if there were total inertia. Imagine you are sitting on the ground and you want to go home. If you were in a state of inertia, you wouldn't be able to get up, you wouldn't be able to walk, stand up, or wear clothes. We, by necessity have to have friction.
Remember, an object must go in a straight line to have inertia. As an experiment, take a rock or a ball and tie it to the end of a string. Twirl it around and you will feel the pull on your finger (gravity = friction). Have it twirled at a generally fast pace and then let go. Does the ball keep going in a circular motion? No, because that is contrary to Newton's first law of motion. It goes in a straight line.
Newton's second law of motion is the relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. In simple terms think about an adult climbing a rope. What would happen if the rope couldn't hold the adult body? It would break and both would tumble down to the ground! Try this simple experiment to show how it works: Take a weight scale on the elevator with you. Stand on it and note your weight as you go up in the elevator. You will discover that you are going to be adding on weight the higher you go. The push upward (acceleration) registered on the bottom of your feet (mass) and is accelerating your body.
The third law is for every action, there is as reaction. Here are some practical examples to show the third law. Let's pretend we are going into a restaurant and you have to push to open the door. You will feel the door pushing back against your hand as you continue to push it open. If you have ever gone target shooting, you will notice that after you push the trigger, the gun or rifle kicks back at you. Bullet forward, gun backward. Imagine yourself in a boat. You have come to shore and you are getting off. As you push yourself forward to get on the dock, your boat will go backwards. It is the same as getting out of a pool. As you pull yourself out of the water, you feel the back tow trying to keep you in the water.
Newton's three laws of motion have given us a greater understanding to physics and a reliable way to understand why we can talk, run, and walk. It helps us understand why a plane is able to take off and land. Many inventions have been made based upon the knowledge of these laws.