What does f = ma mean?

What does f = ma mean?

The correct answer is: F = KMA
Where f is the resultant force acting on the object. Note that it's the resultant force! Unit: n
K is the coefficient of proportionality. In the international system of units, 1 is deleted and omitted
The unit of acceleration must be kg, and the unit of acceleration must be m / S ^ 2
If the unit of M and a is not kg and M / S ^ 2, then K cannot be taken as 1, depending on the situation

How is the expression of Newton's second law f = ma derived in the plane polar coordinate system? What is the physical meaning of each term?
Or tell me about the book?

It's too troublesome to input a bunch of mathematical symbols. It involves the derivation of unit variable vector. Please refer to the first chapter of theoretical mechanics written by Professor Zhou Yanbai

The difference between N and F in high school physics

f: Represents the frequency, which refers to the number of rotations per second, and the unit is: times / second
n: Represents the rotational speed. It refers to the number of rotations per unit time, not necessarily limited to the number of rotations per second. It can be the number of rotations per minute or per hour. The unit can be: times / second, times / min, times / hour
When n times / second, then n = f, so when doing the problem, pay attention to the unit conversion
I feel that the answers upstairs are wrong

Why is f = mg MA in weightlessness

The same as taking an elevator, when you squat, you have a rural acceleration. Your own gravity needs to divide part of the force to produce this acceleration, so you have less pressure on the earth. For example, if you weigh 100kg and the acceleration a = 1m / s when you squat, you will divide the force F = ma = 1 * 100 = 100N in your own gravity 1000N to provide this acceleration, so the earth only needs to support you 900N
In other words, f '= mg Ma, where f' is the supporting force, M is your own mass, and a is the downward acceleration

The frequency of a sinusoidal alternating current is 50 Hz, the effective value is 3a, and the initial phase is - π / 6

i=3√2 sin(314t-π/6) A
among
314=2πf=2*3.14*50

The frequency of a sinusoidal alternating current is 50 Hz, the effective value is 2A
The frequency of a sinusoidal alternating current is 50 Hz, the effective value is 2a, and the initial phase is - 2 / * (* represents the value of PI). Write its instantaneous expression (please also analyze and write the calculation process)

i=2√2sin(2πft-2/π)=2√2sin(100πt-2/π)
In the formula: 2 √ 2 is the peak value of AC current, and the peak value of AC current is √ 2 times of the effective value
2 π f is the angular frequency of alternating current
-2 / π is the initial phase of alternating current
The above formula is the expression of alternating current

What are the RMS and frequency of AC voltage U = 220 (root 2) sin314tv?

The effective value is 220 V and the frequency is 50 Hz
Because 220 root sign 2 is the maximum value, there is such a relationship in the alternating current: effective value = maximum / root sign 2
314=100*3.14=2*3.14/T=2*3.14*f
So we can get f = 50 Hz

The frequency of sinusoidal voltage is 40Hz, the effective value is 2V of 10 root sign, the instantaneous value of T = 0 voltage is 2V of 10 root sign, and the voltage is increasing, so the instantaneous value expression of the voltage is obtained

The expression of voltage instantaneous value is u = 20sin (80 π T + π / 4) v

The specification of a bulb is 220 V, 100 W. set the effective value of the power supply voltage as 220 V, the frequency as 50 Hz, and the initial phase as 0 °. Calculate the instantaneous value expression of the current in the bulb

The premise is that the bulb is assumed to be pure resistance
RMS current = 100W / 220V = 0.4545a, peak value √ 2 * 0.4545 = 0.6428a
The current phase is the same as the voltage
I=0.6428*sin(2*π*50*t)

Why does China use 220 V and some countries use 110 V
Why do we have to do this? Do we have to use transformers when we bring electrical appliances? It's not very troublesome. Why not unify them?

There are many technical implementation schemes, which need to be unified with conditions
1. Technically, we should prove that we are really better than others;
2. There is no patent restriction, that is, it does not involve economic interests
3. National strength and world prestige are stronger than other countries. You can promote your standards all over the world
But in the past 300 years, which country can do it at the same time?
Just like 3G, why there are so many standards? It's not because of the second point. According to the international patent law, you have to pay royalties for using other people's standards. We don't want to see fertilizer flowing into the field of outsiders, so we don't want to unify