When it comes to mechanics, a lot of people get stuck with the words, “to understand, but not to move”. In fact, newton's three laws are not difficult, but rather they are not put in the same frame of thinking. As long as we capture the “reception-movement-change” line, a lot of things go along。
First, grab the mechanics
I'm the one who's afraid of turning the point of knowledge into an island. For example, inertia, acceleration, force, reaction seem to recognize each other, and the issues are confused. A truly efficient way of learning is to build a main line: why objects move, how they move, why they change. Once the main line has been reached, the three main laws will no longer be fragmented conclusions, but complete logic。
The first law tells us that if there is no external force or no combined force, the object will remain active. Its core is not “objects must be static”, but the same. The static can remain the same and the flat-speed straight motion can remain the same. As soon as they saw “objects in motion”, many of them reacted to the situation and thought that there was a strong push, which was a common error。
It is not the same thing to understand the first rule, but to distinguish between “movements” and “changes in the state of movement”. For example, a hockey ball in a slide, if it has little resistance, will continue to move forward, not because it has “still the power to move forward”, but because there is not enough external force to change its state. This will help you jump out of the intuitive trap of powerful talent。
The second law has changed
The second law is the core bridge of the mechanics. It is intended to convey that when objects are subject to combined forces, the state of motion changes, and the speed of change is related to the size and mass of the stress. You don't have to remember complex expressions. The key is to remember one sentence: power is not used to “maintain movement”, but to “change movement”。
Many of our classmates have been able to focus on “power” while forgetting both “quality” and “acceleration direction”. In fact, the force of the same size, in light and heavy objects, has a completely different effect. Light objects are more likely to be pushed, brakeed, turned; heavy objects are more “stable” and their movement is more demanding. That's the hard-won nature of quality influencing movement。
When it comes to the subject of the second law, it is possible to ask itself three questions: do you have a combined force? Where are we headed? How does it want to change things? As long as the “reception direction” and the “change direction” are aligned first, many of the issues are not confused. In particular, in common scenarios such as slopes, ropes and carts, it is often more stable to judge change trends and then to judge the relationship of strength than a direct set of conclusions。
The third law is about relationships
The third law is most easily misunderstood. Many would interpret the force and the reaction as “a pair of offsets”, which are not on the same object and therefore cannot simply be offset against each other. They are characterized by equal size, opposite direction, simultaneous creation and disappearance. Most importantly, they operate on two distinct objects。
You push the wall, you push the wall. You'll feel the reaction, but you won't be unstable because they're offsetting, because they're not in the same stress analysis. When you're doing it, if you mix it up, it's easy to make mistakes. Remember: the third law is about interaction, not balance. The two concepts must be separated。
In order to truly master the third law, it can be understood from the perspective of "a pair appearance". Where there is contact, where there is pull and squeeze, there must be force and reaction. The rope pulls the object, and the object pulls the rope; the ground supports the person, the person presses the ground. As long as you can find another object, it is easier to see on which two objects the force falls。
Three steps
The most effective way to make the three major laws truly serve the examination is not to repeat the definition, but to form a regular process. The first step is to determine who is the subject of the study and not to mix all the power with the force. The second step is to look for external and interactive forces to distinguish between those that work on the same object and those that are not in the same attempt. The third step is to determine whether the object remains in state or changes。
The value of this process is that it can help you to reduce the "look, do wrong" situation. In particular, the choice of the question and the brief answer, many of the errors are not knowledge-based, but the order of analysis is confused. First objects, then stress, then change, are very practical mechanics thinking templates. It is possible to return to the basic logic as long as it is a habit and the title goes around。
In addition, the review should not be carried by a mere “law name”, but rather by living scenes: pushing doors, brakes, walking, driving and lifting objects, all of which correspond to the three main laws. Putting knowledge into the real world will make the memory more stable and better understood. This method is more suitable for debrisification time review than mechanical brushing。
I don't know
The three most common pits must be avoided while studying mechanics. First, there is a misreading of “incapacity” as “no movement”; second, there is a misreading of “powerful” as “certain change in speed”; and third, there is a misperception of force and reaction as balancing forces on the same object. As long as you're clear on these three points, many of the underlying questions are already missing half。
There's also a practical memory technique: the first rule is state, the second law is change, the third law is relationship. It's simple, but it helps you to quickly distinguish the focus of different laws. Don't rush to conclusions, but ask yourself whether the question is whether it is “state” “change” or “interaction”。
If you think that mechanics are always "learning to forget and get confused," it means that you're not missing a point of knowledge, but a way of connecting it. Use the three laws as a set of tools: the first law helps you judge the state, the second law helps you explain the changes, the third law helps you see the relationship. When the tools are used right, the thinking will be fine。
Finally, it is suggested that you use one hour of a lecture review: 10 minutes to recapitulate the core meanings of the three laws, 20 minutes to compare the life examples, 20 minutes to organize common error zones, and 10 minutes to determine whether “objects, stress, change”. This is more effective than a blind brush. Do you want me to go on and say, "how fast do you get in?"
