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The story of Newton's gravity
In 1666, the 23-year-old Newton was still a third year student at Trinity College, Cambridge University. Newton had been puzzled by the following questions: what forces drove the moon to revolve around the earth and the earth around the sun? Why didn't the moon fall on the earth? Why didn't the earth fall on the sun? Sitting in the orchard of his country sister
What is the main content of Newton's classical mechanics
Because Newton's mechanics is very different from modern mechanics (dominated by quantum mechanics and relativity), although Newton's mechanics is not correct in the high-speed and micro field (due to the limitation of the understanding level at that time), it can easily deal with problems in general (low speed and macro), that is to say, Newton's mechanics is wrong but still useful, So I'm going to name them separately. What's their name? Finally, one is called classical mechanics and the other is called modern mechanics
Newton's three laws
Newton's three laws are important laws in mechanics, which are the basis of studying classical mechanics
1. Newton's first law
Content: any object remains stationary or moving in a straight line at a constant speed until it is forced to change this state by the force of other objects
Explanation: all objects have the tendency of keeping still and moving in a straight line at a constant speed. Therefore, the motion state of an object is determined by its motion speed. Without external force, its motion state will not change. This property of an object is called inertia. So Newton's first law is also called inertia law. The first law also clarifies the concept of force. It is clear that force is the interaction between objects, It is pointed out that force changes the motion state of an object. Because acceleration describes the change of the motion state of an object, force is related to acceleration rather than speed. If we don't pay attention to this point in our daily life, it is easy to produce illusion
Note: Newton's first law does not hold in all reference frames. In fact, it only holds in inertial reference frame. Therefore, whether Newton's first law holds or not is often regarded as the criterion of whether a reference frame is inertial reference frame
2. Newton's second law
Content: the object will produce acceleration under the action of combined external force. The direction of acceleration is the same as that of combined external force. The magnitude of acceleration is directly proportional to the magnitude of combined external force and inversely proportional to the inertial mass of the object
The second law quantificationally describes the effect of force and quantifies the inertia of an object. It is vector and instantaneous
It should be emphasized that the external force on the object will produce acceleration, which may change the motion state or speed of the object, but this change is related to the motion state of the object itself
In vacuum, because there is no air resistance and all kinds of objects are only subjected to gravity, they all have the same acceleration regardless of their mass. Therefore, when they fall freely, their velocity changes are the same in the same time interval
Newton's third law
Content: the force and reaction between two objects are equal in size and opposite in direction on the same straight line
Explanation: in order to change the motion state of an object, there must be other objects interacting with it. The interaction between objects is reflected by force. It also means that the action of force is mutual, and there must be reaction force if there is action. They act on the same straight line with equal size and opposite direction
It should also be noted that:
(1) Acting force and reaction force are not primary and secondary, successively. They produce and disappear at the same time
(2) This pair of forces act on different objects and cannot be counteracted
(3) Force and reaction must be forces of the same nature
(4) It has nothing to do with the frame of reference
Have you heard of the famous Newton's law of gravitation?
There is an attractive force between any two objects. If the masses of two objects are M1 and M2 respectively, and the distance between them is D, then the gravitational force between them is the square of F = gm1m2 / D (G is a constant), At this point, D is the radius of the earth, R. the gravity of a person standing on the moon will be a fraction of the gravity of the earth's surface (reference data: the mass of the moon is about 10 / 801 of the mass of the earth, and the radius of the moon is 100 / 367 of the radius of the earth)?
The gravity on the moon is greater than that on the earth
＝[GM_ (month) m / R_ (month) ^ 2] / [GM]_ M / R_ (land) ^ 2]
＝M_ (month) r_ (land) ^ 2 / M_ (land) r_ (month) ^ 2
= 10 * 367 ^ 2 / 801 * 100 ^ 2 = 0.16815
It seems to be one sixth
Why did Newton discover the law of universal gravitation?
This accident accounts for a large proportion, but it is absolutely inseparable from his daily accumulated efforts. Even without this apple incident, I believe there will definitely be other peach, Sydney and other incidents. It is inevitable to say that it is accidental
What formula is f1l1 = f2l2? What do F1, L1, F2, L2 stand for
F1l1 = f2l2 is the formula of lever balance condition
F1: Power
L1: resistance
F2: power arm
L2: resistance arm
This is knowledge of physics
The motion (acceleration and free falling motion) formula includes the deformation formula
1) The results show that: 1. Average velocity vt2 = s / T (definition) 2. Useful inference vt2-vo2 = 2As 3. Middle time velocity VT / 2 = vt2 = (VT + VO) / 2 4. Final velocity VT = VO + at 5. Middle position velocity vs / 2 = [(VO2 + vt2) / 2] 1 / 2 6. Displacement S = vt2 t = VT + at2 / 2 = VT / 2T 7
Who knows what P means in physics
This one is used more and has different meanings
Capital P is generally power
There are also p-channel MOS transistor, capacitance pf
What unit does P represent in physics? What unit does w represent in physics
Power watt w
Work Joule J
What does P = w / s mean in physics
In the power of mechanical work, the formula P = w / T represents the work done by an object in unit time, that is, power. It is a physical quantity to measure the speed of work done by an object. The higher the power, the faster the work done by the object. In the case of controlling variables, it can also be described as follows: (1) at the same time of doing work, the less time the object takes, the greater the power
The exact meaning of W in P = w / T in Physics
P is the power, that is, the amount of work done per unit time, which indicates the speed of your work, that is, the problem of efficiency. W is the work, which is equivalent to the energy you pay for your work, and t is the time. See the textbook for details, which is very clear
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