PFC Chapter 114 Grade 1 Physics Class
Chapter 114 Grade 1 Physics Class
The afternoon sun lazily streamed into the classroom of Class 11. The students had just finished their lunch break and were still sleepy as they prepared for their afternoon physics class. Li Shiqing sat by the window, her eyes fixed on the students having PE class on the playground outside, but her thoughts were already drifting back to the classroom, because her physics class, which she both loved and dreaded, was coming up.
Liu Yixin nudged Li Shiqing from behind and handed her a small note that read: "We're going to have to 'take a plane' in physics class again later, what should we do?"
Li Shiqing smiled helplessly and was about to reply to the note when she heard the physics teacher's loud voice: "Class, class is starting!"
Zhang Chen, the class representative for physics and a physics prodigy, noticed Li Shiqing's blank expression and leaned over to whisper, "Shiqing, don't look so worried. Physics isn't that scary. Ask me if you don't understand anything."
The physics teacher stood on the podium, cleared his throat, and said, "Class, today we're going to talk about Newton's Second Law. This law is like a magic spell in the physics world; mastering it will solve many problems. For example, the greater the force acting on an object, the greater its acceleration, provided that its mass remains constant. It's like pushing a cart; the more force you use, the faster the cart goes. But if the cart is full of heavy objects, you'll need to use even more force to make it go faster."
As the teacher spoke, she wrote the formula "F = ma" on the blackboard. Li Shiqing looked at the formula and muttered to herself, "These letters look simple, so why are they so hard to understand?"
Zhang Chen smiled and said, "Shi Qing, look, F is force, m is mass, and a is acceleration. For example, if you use a force of 10 Newtons to push an object with a mass of 2 kilograms, then according to this formula, its acceleration is 5 meters per second squared. Just like when you kick a soccer ball, the more force you use, the faster the soccer ball flies, and the more obvious the change in its state of motion is. This is the manifestation of a large acceleration."
Liu Yixin, who was listening nearby, seemed to understand but not quite: "Then how do you determine what forces are acting on an object? I never understand this when I do problems."
The physics teacher seemed to have overheard their discussion and came over with a smile, saying, "That's a good question. Class, to determine the forces acting on an object, we must first identify the object of our study, and then see what forces are acting on it around it. For example, a book placed on a table experiences gravity, which acts vertically downwards and is equal in magnitude to its mass multiplied by the acceleration due to gravity, g. It also experiences a supporting force from the table, which acts vertically upwards and is equal in magnitude to its weight. This is how the book remains stationary on the table. It's like a game of balancing forces, where various forces interact to reach a stable state. Another example is an object on an inclined plane. Besides gravity and the supporting force, it may also experience friction, the direction of which is opposite to the direction of the object's relative motion or tendency to move relative to it."
Li Shiqing suddenly had a flash of inspiration: "Teacher, what if an object is in water? Wouldn't the forces acting on it be more complex?"
The teacher looked at Li Shiqing approvingly: "Excellent question! When an object is in water, in addition to gravity, it is also subject to buoyancy. The magnitude of the buoyancy is equal to the weight of the liquid displaced by the object. For example, an iron block will sink in water because its weight is greater than the buoyancy; while a piece of wood will float because the buoyancy is equal to its weight. It's like objects in water playing a game of 'floating and sinking,' and whoever has the greater force wins."
Zhang Chen continued, "Teacher, what if the object is in the water and is subjected to other forces? For example, someone is pulling it with a rope."
The teacher smiled and replied, "Then we should analyze all the forces, and according to the method of force composition and decomposition, convert these forces into several simple forces, and then use Newton's second law to calculate the object's acceleration or other states of motion. Just like a jigsaw puzzle, by piecing together the pieces of various forces and finding their resultant force, we can know exactly how the object will move."
Liu Yixin said with distress, "Teacher, I still find it so difficult. All these thoughts are a jumbled mess in my head."
The teacher encouraged, "Don't rush. Physics is a subject that requires a lot of thinking and practice. You can do some simple force analysis exercises, starting with simple cases, and you'll gradually master the tricks. For example, start by analyzing an object on a horizontal surface that is only subjected to one pulling force, and then gradually increase the types of forces and the motion of the object. Just like learning to walk, take it one step at a time. First, stand firmly, and then slowly start running."
Li Shiqing and Liu Yixin nodded and began to take notes seriously. With Zhang Chen and the teacher's explanation, Newton's second law didn't seem so mysterious and scary anymore.
As the lesson progressed, the teacher discussed the application of Newton's Second Law in daily life: "Students, when we are in a car, if the car suddenly accelerates, we feel our bodies lean backward. This is because our bodies have inertia to maintain their original state of motion, while the car's acceleration requires a forward force. This force creates a relative tendency for our bodies and the car to move, so we feel like we are leaning backward. This is a small example of Newton's Second Law in life. Physics is actually everywhere; it is in our daily lives, waiting for us to discover and understand it."
Zhang Chen excitedly asked, "Teacher, is it the same principle that our bodies lean forward when a car brakes?"
The teacher smiled and said, "That's right! When a car brakes, its speed suddenly decreases, but our bodies still want to maintain the original speed and continue moving forward, so we lean forward. It's like when we suddenly stop running, our bodies will also lurch forward due to inertia. Physics is like that; it uses simple laws to explain many seemingly ordinary phenomena in our lives that contain scientific principles."
Li Shiqing also began to actively participate in the discussion: "Teacher, does the airplane also utilize Newton's second law when it takes off?"
The teacher nodded: "When an airplane takes off, the thrust generated by the engine accelerates the plane. When the plane reaches a certain speed, the airflow speed on the upper and lower surfaces of the wing is different, generating upward lift. When the lift is greater than the plane's weight, the plane takes off. This involves the relationship between force and acceleration in Newton's second law, as well as knowledge of fluid mechanics. Physics knowledge is interconnected, and you should learn to apply what you've learned to other situations."
In this fascinating physics class, Li Shiqing, Liu Yixin, and their classmates, led by their teacher and Zhang Chen, seemed to step into a world of physics full of amazing phenomena. The originally dry formulas and theorems gradually became vivid, like keys that unlocked doors to the mysteries of science, filling everyone with enthusiasm and anticipation for exploring physics. And this is just the beginning of their voyage in the ocean of physics knowledge; many more wonderful journeys await them in the future.