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1. The composition and decomposition of forces

because the speed is 0 at this time, the centripetal force is 0, so the decomposition diagram of the force can be drawn, that is, the component force of gravity in the direction of

rope is equal to the tensile force on the rope, but the direction is opposite. According to the angle of the rope,

degree, the component of gravity can be calculated, so the pull of the ball is small

2. Does Newton penlum need force

3.

Calculation formula: ft = {MV

F is the average force, t is the time, M is the mass of the object, V is the velocity, and} is the variation; This formula is understood as that the impact force and its time acting on the object are equal to the change of momentum of the object

impact force refers to the force that appears when objects collide with each other. In the process of collision or striking, the force that suddenly increases and then rapidly disappears between objects is also called impact force or impact force. The characteristic of the impact force is that the action time is very short, but the magnitude can be very large. "

The impact force of this fluid is e to the continuous interaction between the fluid (such as water) and the object, resulting in impact force. The difficulty lies in the selection of research object and research process

extended data

usually, the solution of this kind of problem should focus on two points:

(1) using the "infinitesimal method" to determine the research object and research process: because the fluid is continuously interacting with the object, we can select a short period of time Δ T to determine the object. As mentioned above: in Δ T time, our research object is actually in the figure Δ Water in part X

what is the quality of this part of water Δ m= ρ S′v Δ T -- because the time is very short, the speed of water rising for a short distance can be regarded as constant; In addition, it should be noted that when the water reaches this position, the cross-sectional area becomes s ′, and s ′ is unknown. Because the water is continuous, combined with the first question,

Δ m= ρ S′v Δ t＝ ρ SVo Δ T

(2) ignoring the gravity of water. When using the micro element method to deal with the problem, the gravity and the impact force can be compared slightly< br />

4. Find out the total mass and the center of gravity position of the object to be rotated, multiply them to be the initial moment, and then multiply them by an appropriate safety factor.

5. It's similar to the nature of pyramid selling. It's about investing in mining machines. In the end, it's about buying and selling empty. It's about relatives and friends who have made money for future generations

6. 1) Common forces
1. Gravity g = mg
(vertical downward, g = 9.8m / S2 ≈ 10m / S2, acting point at the center of gravity, applicable to the earth surface)
2. Hooke's law f = KX
{direction along the recovery deformation direction, K: stiffness coefficient (n / M), X: deformation variable (m)}
3. Sliding friction f = μ FN
{opposite to the relative motion direction of the object, μ： Friction coefficient, FN: positive pressure (n)}
4. Static friction 0 ≤ F, static ≤ FM
(opposite to the relative motion direction of the object, FM is the maximum static friction)
5. Gravitation f = gm1m2 / r2
(g = 6.67) × Electrostatic force F = kq1q2 / r2
(k = 9.0) × 7. Electric field force F = EQ
(E: field strength n / C, Q: electric quantity C, the electric field force of positive charge is the same as the direction of field strength)
8. Ampere force F = bilsin θ < br /> θ When l ⊥ B: F = bil, B / / L: F = 0)
9. Lorentz force F = qvbsin θ< br /> θ When v ⊥ B: F = QVB, V / / B: F = 0)
note:
(1) the stiffness coefficient K is determined by the spring itself
(2) friction coefficient μ It has nothing to do with the pressure and contact area, but is determined by the material characteristics and surface condition of the contact surface
(3) FM is slightly larger than that of FM μ FN, generally regarded as FM ≈ μ FN;
(4) other related contents: static friction (size and direction) [see P8 in Volume 1]< (5) symbols and units of physical quantities

(1) the centripetal force can be provided by a specific force, a resultant force or a component force, and its direction is always perpendicular to the direction of velocity and points to the center of the circle
2) the centripetal force of an object in uniform circular motion is equal to the resultant force, and the centripetal force only changes the direction of velocity, not the size of velocity, so the kinetic energy of the object remains unchanged, the centripetal force does not do work, but the momentum changes constantly< Kepler's third law:
T2 / R3 = K (= 4) π 2 / GM)
{R: orbital radius, t: period, K: constant (independent of planetary mass, depends on the mass of central celestial body)}
2. Law of universal gravitation:
F = gm1m2 / r2
(g = 6.67 × Gravity and gravitational acceleration on celestial bodies:
GMM / r2 = mg
G = GM / r2
{R: celestial body radius (m), M: celestial body mass (kg)}
4< br /> ω＝( GM/r3)1/2< br />T＝2 π( R3 / GM) 1 / 2
{M: mass of central celestial body}
5. The first (second and third) cosmic velocity
V1 = (g earth r earth) 1 / 2 = (GM / R earth) 1 / 2 = 7.9km/s< br />V2＝11.2km/s
V3 = 16.7km/s
6. Geostationary satellite
GMM / (R + H) 2 = M4 π 2 (r earth + H) / T2
{h ≈ 36000km, H: height from the earth's surface, R earth: radius of the earth}
note:
(1) the centripetal force required for the motion of celestial bodies is provided by universal gravitation, f direction = f ten thousand
(2) the mass density of celestial bodies can be estimated by using the law of universal gravitation< (3) the geostationary satellite can only operate over the equator, and its operation cycle is the same as the earth rotation cycle
(4) when the orbit radius of the satellite becomes smaller, the potential energy becomes smaller, the kinetic energy becomes larger, the velocity becomes larger, and the period becomes smaller
(5) the maximum orbit speed and the minimum launch speed of the earth satellite are 7.9km/s
hope to help you

7. Black is relative. How can there be a definition? There are also local tyrants, powerful people and tramps in the United States. There are also local leaders and petitioners in China. This world is like this, the jungle, regardless of national boundaries. If you have to ask how dark it is, go out and have a look. Naturally, you will feel it.

8.

F = ma.

where f and a are forces and accelerations; M is the mass of the object. If M and a on the right of the formula are known, then this formula is the definition of force. So in absolute system, mass is the basic quantity and force is the derived quantity

The dimension of

force is mlt-2, where m, l and T are the dimensions of mass, length and time respectively. In dynamics, it is equal to the proct of the mass and acceleration of the object

the weight of any object is measured by the weight of a standard object. Let the weight of an object be w, then its mass m can be written as w / g. The dimension of the derived quantity m is ft2l-1, where f is the dimension of the force

since the gravitational acceleration of the earth is not exactly equal everywhere on the earth's surface, the weight of objects everywhere on the earth's surface will not be exactly equal. In order to avoid this difficulty, a specific point on the earth's surface is defined as the place to measure the standard weight of the standard object

Six properties of Newton's second law: causality: force is the cause of acceleration

Vectoriality: both force and acceleration are vectors, and the direction of acceleration is determined by the direction of external force. In the mathematical expression of Newton's second law ∑ f = ma, the equal sign not only means that the values on the left and right sides are equal, but also means that the direction is the same, that is, the acceleration direction of the object is the same as the direction of the external force

3. Instantaneity: when the external force on an object (with a certain mass) changes suddenly, the magnitude and direction of acceleration determined by the force will also change abruptly; When the external force is zero, the acceleration is zero at the same time, and the relationship between acceleration and external force remains one-to-one. Newton's second law is a law of instantaneous correspondence, which indicates the instantaneous effect of force

Relativity: there is a kind of coordinate system in nature. In this kind of coordinate system, when the object is not forced, it will keep a uniform linear motion or static state. This kind of coordinate system is called inertial reference system. The ground and the object that is stationary or moving in a straight line at a constant speed relative to the ground can be regarded as inertial reference frame, and Newton's law is only valid in inertial reference frame

Independence: each force acting on the object can proce an acceleration independently, and the vector sum of the acceleration proced by each force is equal to the acceleration proced by the combined external force

Identity: A and f correspond to a certain state of the same object

9. And then the class??

10. In fact, the fun of Diablo lies in painting. Blizzard's design principle also lies in this. As long as you know its intention, I suggest that the progress at least go to Chapter 4 of purgatory. Depending on your personal situation, upgrade the equipment and brush the tower, which is the picture of Spider Woman + AZ. The progress directly goes from the penultimate to the next, which is about 5 or 6 floors to spider, and then to AZ, It's OK to brush here repeatedly, because the elite monsters here are more concentrated, and it's easy to stack buffs. There's a good chance that 5buff can kill the boss when you go to spiders, which is relatively high. In early June, when I was hunting for 8-12 pieces of gold every 30 minutes, I hope to adopt it. After upgrading here, I suggest farm Chapter 4, stack 5buff to make a big pineapple