![]() As a second example, think about the motion of a high speed train (Shikansen train shown below Mount Fuji in the image below). It is not stopping just because no one is pushing it any more! It wants to keep moving and you will have to have a strong (and potentially painful) interaction with it in order to get it to stop. Here your intuition is (or should be!) that you do not want to catch this ball with your bare hands. More than that, we have intuition in other circumstances that seem to contradict what we naturally feel about the motion of the piano.Ĭonsider that you are playing baseball and catching the pitches of a pitcher throwing a ball with a mass of about 150 grams at 40 meters/second (90 miles/hour). When we stop pushing, those other forces do not go away, so they have to be considered in deciding what it is that is happening to the piano. It also interacts with the earth via gravity and the floor via normal and frictional forces - and these forces are as large or larger than the forces we exert. When we are pushing a piano, we are not the only object interacting with it. When you stop pushing on the ground in order to walk, you just stop.īut these intuitions are a bit tricky. When you stop pushing, it quickly comes to a stop.Ī second example is just your own motion when you walk. If we want to move a piano across a floor, we have to push in order to start it and continue to push in order to keep it going. This would only be a thought experiment since on the earth there are always interactions, starting with gravity.) The first intuition we might typically have is that if you want to get something moving and keep it moving, you have to push it. ![]() Once we have decided what objects and interactions we have, we need a starting point: What happens to an object (or system of objects) when all the interactions on it balance? (Or, one might consider what happens to an object if there are no interactions acting on it. For this, tools such as System Schema and Free-Body Diagrams help. In Newton's 0th law, we have identified that what we have to do first is identify objects and interactions. We want these principles to be general - to hold for all circumstances as long as we have carefully defined them. ![]() In formulating our observations and understanding of how objects move, we need to coordinate our variety of experiences and intuitions together with what we have learned from our experiments into coordinating principles.
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