How to calculate the force of an object

1. If a person wants to push an object, then the force F given to the object should be equal to or greater than the friction f between the object and the ground, that is, the steps should be like this! In order to make the object move, f = f (friction) and f (friction) = mg * u (U is the friction coefficient) can be solved by numerical method.

2. It depends on the volume. For example, if a piece of 100 square meters paper weighs 1 kg and hits people, do you think people will die? Of course not!

4. It can be explained by the momentum theorem: △ VM = ft, f is the average force. The action time t is very short, we assume it is 0.01s. Assuming that the ball is a basketball, the quality of the basketball should not be less than 567g, not more than 650g, we take 0.5kg for convenience. If the velocity of 1 meter per second impacts a person, the average force is 50 Newton; And when you hit a person at a speed of 4 meters per second, the average force is 200 newtons, so it's much more painful. Data: derivation: take F = ma... Newton's second law of motion into v = V0 + at to get v = V0 + ft / m, simplify to VM - v0m = ft, and take VM as the quantity describing the state of motion, which is called momentum 1) Content: the impulse of resultant force is equal to the change of momentum. Expression: ft = MV ′ - MV = P ′ - P, or ft = △ P, f in the momentum theorem formula is the resultant force of all external forces including gravity on the research object. It can be a constant force or a variable force. When the external force is a variable force, f is the average value of the external force on the action time. P is the initial momentum of the body, p 'is the final momentum of the body, and t is the action time of the combined external force 2) F △ t = △ MV is a vector. When applying the momentum theorem, we should follow the parallelogram table rule of vector operation, or we can use the orthogonal decomposition method to transform vector operation into scalar operation. Suppose that FX (or FY) is used to represent the component of the combined force on the X (or y) axis Then FX △ t = mvx-mvx0, FY △ t = mvy-mvy0. The above two formulas show that the component of impulse of combined force on a certain coordinate axis is equal to the component of increment of momentum on the same coordinate axis. When we write the component equation of the momentum theorem, for the known quantity, the positive value is taken for those in the same direction as the positive direction of the coordinate axis, and the negative value is taken for those in the opposite direction; For unknown variables, it is generally assumed that the direction is positive, if the calculation result is positive. It indicates that the actual direction is consistent with the positive direction of the coordinate axis. If the calculation result is negative, it indicates that the actual direction is opposite to the positive direction of the coordinate axis.

5. 1. Force (f): force is the action of an object on an object
the forces between objects are always mutual
unit of force: Newton (n)
force measuring instrument: dynamometer; The laboratory uses a spring dynamometer
the effect of force: make the object deform or change the motion state of the object
the change of object motion state refers to the change of object velocity or motion direction
2. The three elements of force: the size, direction and action point of force are called the three elements of force
the diagram of force should be scaled; A schematic diagram of the force without scale< Gravity g: the force exerted on an object e to the attraction of the earth. Direction: vertical down
relationship between gravity and mass: g = mg, M = g / g
G = 9.8 N / kg. Pronunciation: 9.8n/kg, which means that the gravity of an object with a mass of 1kg on earth is 9.8N< Center of gravity: the point where gravity acts is called the center of gravity of an object. The center of gravity of regular object is on the geometric center of the object, and the center of irregular object may or may not be on the object< (4) two force equilibrium conditions: acting on the same object; The two forces are equal in magnitude and opposite in direction; Acting on a straight line
under the balance of two forces, an object can be stationary or move in a straight line at a constant speed
the equilibrium state of an object means that the object is in a state of static or uniform linear motion. The resultant force of the external force on an object in equilibrium is zero
5. Combination of two forces on the same line: same direction: resultant force F = F1 + F2; The direction of resultant force is the same as that of F1 and F2
the direction is opposite: the resultant force F = F1-F2, and the resultant force direction is the same as that of the large force
⒍ under the same conditions, rolling friction is much smaller than sliding friction
the sliding friction is related to the normal pressure, material properties and roughness of the contact surface Newton's first law is also known as the law of inertia, whose content is that all objects always keep static or uniform linear motion when they are not affected by external forces
inertia: an object has the property of keeping the original static or uniform linear motion state, which is called inertia

buoyancy
1. Buoyancy and its causes: an object immersed in liquid (or gas) is supported vertically by liquid (or gas), which is called buoyancy. Direction: vertical upward; Cause: the pressure difference between the liquid and the object
2. Archimedes principle: an object immersed in liquid is subject to upward buoyancy, and the buoyancy is equal to the gravity of the object expelling the liquid
that is, f floatation = g liquid discharge = ρ Liquid GV discharge V-row represents the volume of liquid discharged by the object)
3. Buoyancy calculation formula: F floating = G-T = ρ When the object floats: F floats = g object and ρ Things & lt; ρ Liquid when the object is suspended: F floating = g object and ρ Things= ρ Liquid
when the object floats up: F floats & gt; G and ρ Things & lt; ρ Liquid when an object sinks: F floats & lt; G and ρ Things & gt; ρ Gravity g = mg
(vertical down, 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

6. Hello
using the gravity formula: g = mg
G is generally 9.8n/kg
10N / kg is often taken for the convenience of calculation
hope to adopt!

7. We should know the mass of the object m
the friction coefficient of the ground μ
angle between tensile force and horizontal plane α
the tensile force F= μ mg/cos α( Where G is the acceleration of gravity)

8. Hello, this needs to consider the moment of inertia, consider the moment of inertia, use the moment of momentum balance conditions to set up equations, or use simple force system balance conditions

9. The weight that an object can bear is hard to measure. It has something to do with the structure of the object.
for example, the stable structure of a triangle. So the weight that a triangle bears is larger than that of a quadrilateral, and it is not easy to change its shape.
it has nothing to do with its own gravity and the area under force, With regard to the area under force, do you want to ask how much pressure an object can bear
the pressure is related to the stress area. The larger the stress area is, the smaller the pressure is