The relationship between an object’s mass m, its acceleration a, and the applied force F is F = m a. Before we continue with his other two laws, let’s review some of the important history that informed them. Newton owed much to events and people who preceded him. In fact, the marble-and-ramp thought experiment described previously is credited to Galileo. That honor goes to Galileo and to René Descartes.
Interestingly, Newton wasn’t the first scientist to come up with the law of inertia. In this case, the marble will neither slow down nor speed up. Finally, you push a marble on a ramp that represents the middle state between the first two - in other words, a ramp that is perfectly horizontal. Now, you give a gentle push to the marble going uphill on the second ramp. The marble speeds up on its way down the ramp. You let a marble roll down the first ramp, which is set at a slight incline. Also imagine that the ramps are infinitely long and infinitely smooth. But imagine that you have three ramps set up as shown below. The “forever” part is difficult to swallow sometimes. An object in motion will stay in motion, traveling in a straight line, forever, until something pushes or pulls on it. An object at rest will stay at rest, forever, as long as nothing pushes or pulls on it. Let’s restate Newton’s first law in everyday terms: This we recognize as essentially Galileo’s concept of inertia, and this is often termed simply the “Law of Inertia”. That example is similar to the kick when a gun fires a bullet forward.Newton’s First Law of Motion: Law of Inertia The force pushing the ball out was equal to the force pushing the cannon back, but the effect on the cannon is less noticeable because it has a much larger mass. When the cannonball is fired through the air (by the explosion), the cannon is pushed backward. There's also the example of shooting a cannonball. Acting forces encounter other forces in the opposite direction. Your body exerts a force downward and that chair needs to exert an equal force upward or the chair will collapse. The third law says that for every action (force) there is an equal and opposite reaction (force). The difference in effect (acceleration) is entirely due to the difference in their masses. The effect of a 10 newton force on a baseball would be much greater than that same force acting on a truck. The effect (acceleration) on the smaller mass will be greater (more noticeable). The second law shows that if you exert the same force on two objects of different mass, you will get different accelerations (changes in motion). The second law says that the acceleration of an object produced by a net (total) applied force is directly related to the magnitude of the force, the same direction as the force, and inversely related to the mass of the object (inverse is a value that is one over another number. You will learn all the real details - and math - when you start taking more advanced classes in physics.). If they threw something when doing a spacewalk, that object would continue moving in the same direction and with the same speed unless interfered with for example, if a planet's gravity pulled on it (Note: This is a really really simple way of descibing a big idea. The same is true when they throw objects for the camera. There is no interfering force to cause this situation to change. Have you ever noticed that their tools float? They can just place them in space and they stay in one place. You can see good examples of this idea when you see video footage of astronauts. If you're going in a specific direction, unless something happens to you, you will always go in that direction. If nothing is happening to you, and nothing does happen, you will never go anywhere. Motion (or lack of motion) cannot change without an unbalanced force acting. The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed. The ideas have been tested and verified so many times over the years, that scientists now call them Newton's Three Laws of Motion. During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics). He worked on developing calculus and physics at the same time. A little bit stuffy, bad hair, but quite an intelligent guy. There was this fellow in England named Sir Isaac Newton.