4 Fundamental forces and Newton's 3 laws
There are 4 fundamental forces.
(1) Gravitational force
(2) Electric-Magnetic force
(3) Strong force
(4) Weak force
The source of Gravitational force is mass.
If there is two masses, they interact each other.
Imagine that in the universal, there is only one stone with having mass.
Of course naturally stone has mass. We don't need to mention "with having mass".
But sometimes we can imagine special situation through "thought experiment". So stone with no having mass can be existed through "thought experiment".
And then suddenly another stone with having mass was occupied on certain space which is 1,000km from first one.
gra
Then what will be happened?
The two masses will feel attraction force. So two stones will get closer, after all they will be crushed each other.
Newton found out this force. As you know, he is famous of the story regarding "falling apple to the ground of the Earth". Why the apple fall to the ground? Or Why a ball fall to the ground?
It's because of gravitational force between apple and Earth. More strictly speaking, two masses are attracting each other. Apple's mass and Earth's mass are generating gravitational force so that they are getting closer. However when we see real situation it seems like only apple moves to the ground of the Earth.
Why? Think about it.
Yes, because the Earth's mass is so big in compare with apple.
Below is mathematical expression for Gravitational force.
F = G * m1 *m2 / r2
G : gravitational contant
m1 : a matter's mass
m2 : another matter's mass
r : distance between m1 and m2
I'll introduce you Newton's 3 laws.
(1) the law of inertia
(2) the acceleration law --> F = ma
(3) the law of action and reaction
I've told you in physics especially we are interested in movement of (an) object(s). The representative physics quantity for the movement is velocity. To change velocity, acceleration is needed. And for acceleration, external net force which is interacting on an object is needed. So where there is acceleration external net force exits. And where there is external net force, acceleration exits.
And the force always exists by pairing with acting force and reaction force, and the acting force and reaction force has the same magnitude but opposite direction. It's 3rd rule which is, so we called, the law of action and reaction.
Therefore we can conclude that, the apple is affected by gravitational force toward Earth. And gravitational force also is affecting on Earth toward apple. The size of force is the same but the direction is opposite.
Then let's check the second rule. We are familiar with it, because we've studied about equation of motion before. F = ma, this is equation of motion.
F1 = m1 a1 --> G*m1 m2/r2 = m1 a1 --> a1 = G*m2 /r2
F2 = m2 a2 --> G*m1 m2/r2 = m2 a2 --> a2 = G*m1 /r2
Compare a1 and a2.
HW1) Find out Earth's mass with any reference. And then write down by MKS unit.
HW2) Find out Earth's radius with any reference. And then write down by MKS unit.
HW3) Find out Gravitational constant. And then write down by MKS unit.
HW4) If the apple's mass, m1 is 1kg, and it is positioned on 100 m height from ground, What is a1 and a2?
What can we conclude through the result?
Let's look into "the law of inertia". If there is no acceleration on a matter, there is no change of velocity with respect to time. If no acceleration the magnitude and direction of velocity will not change.
When a stone is moving in space with 10 m/s toward north direction, and if there is no external forces that makes acceleration, it moving in space with the same magnitude and the same direction with initial velocity.
It's the law of inertia.
HW5) Research about "Galileo's thought experiment". Describe for it and find out what's the purpose of it.
elee
Electron-Magnetic force is another fundamental force. It's dominated in microscopic world. But in our life we can experience it through magnet and static electricity. Simply speaking for it, "if we divide a matter into very microscopically, it's configured by atoms. And in an atom there are two particles. One is proton and another is electron. All atoms are made of a nucleus and electrons. And nucleus is consisted with proton and neutron. one proton has ( +1.60×10-19C ) as quantity of electric charge, and one electron has ( - 1.60×10-19C ) as quantity of electric charge." So charges are the source of the force.
F = k * q1 q2 / r2 (Coulomb's law)
k : Coulomb constant
q1 : quantity of electric charge for a particle (or matter)
q2 : quantity of electric charge for another
r : distance between q1 and q2
HW6) Find out "k", Coulomb constant and electron's mass.And then write down by MKS unit.
Gravitational force has only attraction force. But Electron-Magnetic force has also repulsive force.
When q1 and q2 are the same charge, the force is repulsive for two particles. And if q1 and q2 are different charge each other, the force is attractive.
atom
Let's look into nucleus. Nucleus includes protons and neutrons. Neutron has no charge.
Anyway in nucleus protons are there together.
Isn't it strange? I said if there are the same charges they repulse each other. Then how can they be together?
We can forecast it in many ways. But the conclusion already made for it is that there is another force.
It's "Strong force". I won't comment for it. Cause it's so difficult academic area. I will skip it.
What we can know now is that "Strong force" is bigger than "Electron-Magnetic force". Otherwise the protons can not stay with each other and they should be scattered because of repulsive forces.
Last fundamental force is "Weak force". When we consider about "Strong force", matter's mass can not be reduced by itself. But in some material, atoms number reduces with respect to time. After "half life" the atoms number decrease into half. It means material's mass reduced by half after half life.
What is the reason? It's because of "Weak force". It's not strong than other fundamental forces in a moment.
But as time goes by weak force become dominant. I will not also explain it deeply.
Let's wrap up in here.
Hope this course would give you good inspiration.
See you next time.
(1) Gravitational force
(2) Electric-Magnetic force
(3) Strong force
(4) Weak force
The source of Gravitational force is mass.
If there is two masses, they interact each other.
Imagine that in the universal, there is only one stone with having mass.
Of course naturally stone has mass. We don't need to mention "with having mass".
But sometimes we can imagine special situation through "thought experiment". So stone with no having mass can be existed through "thought experiment".
And then suddenly another stone with having mass was occupied on certain space which is 1,000km from first one.
gra
Then what will be happened?
The two masses will feel attraction force. So two stones will get closer, after all they will be crushed each other.
Newton found out this force. As you know, he is famous of the story regarding "falling apple to the ground of the Earth". Why the apple fall to the ground? Or Why a ball fall to the ground?
It's because of gravitational force between apple and Earth. More strictly speaking, two masses are attracting each other. Apple's mass and Earth's mass are generating gravitational force so that they are getting closer. However when we see real situation it seems like only apple moves to the ground of the Earth.
Why? Think about it.
Yes, because the Earth's mass is so big in compare with apple.
Below is mathematical expression for Gravitational force.
F = G * m1 *m2 / r2
G : gravitational contant
m1 : a matter's mass
m2 : another matter's mass
r : distance between m1 and m2
I'll introduce you Newton's 3 laws.
(1) the law of inertia
(2) the acceleration law --> F = ma
(3) the law of action and reaction
I've told you in physics especially we are interested in movement of (an) object(s). The representative physics quantity for the movement is velocity. To change velocity, acceleration is needed. And for acceleration, external net force which is interacting on an object is needed. So where there is acceleration external net force exits. And where there is external net force, acceleration exits.
And the force always exists by pairing with acting force and reaction force, and the acting force and reaction force has the same magnitude but opposite direction. It's 3rd rule which is, so we called, the law of action and reaction.
Therefore we can conclude that, the apple is affected by gravitational force toward Earth. And gravitational force also is affecting on Earth toward apple. The size of force is the same but the direction is opposite.
Then let's check the second rule. We are familiar with it, because we've studied about equation of motion before. F = ma, this is equation of motion.
F1 = m1 a1 --> G*m1 m2/r2 = m1 a1 --> a1 = G*m2 /r2
F2 = m2 a2 --> G*m1 m2/r2 = m2 a2 --> a2 = G*m1 /r2
Compare a1 and a2.
HW1) Find out Earth's mass with any reference. And then write down by MKS unit.
HW2) Find out Earth's radius with any reference. And then write down by MKS unit.
HW3) Find out Gravitational constant. And then write down by MKS unit.
HW4) If the apple's mass, m1 is 1kg, and it is positioned on 100 m height from ground, What is a1 and a2?
What can we conclude through the result?
Let's look into "the law of inertia". If there is no acceleration on a matter, there is no change of velocity with respect to time. If no acceleration the magnitude and direction of velocity will not change.
When a stone is moving in space with 10 m/s toward north direction, and if there is no external forces that makes acceleration, it moving in space with the same magnitude and the same direction with initial velocity.
It's the law of inertia.
HW5) Research about "Galileo's thought experiment". Describe for it and find out what's the purpose of it.
elee
Electron-Magnetic force is another fundamental force. It's dominated in microscopic world. But in our life we can experience it through magnet and static electricity. Simply speaking for it, "if we divide a matter into very microscopically, it's configured by atoms. And in an atom there are two particles. One is proton and another is electron. All atoms are made of a nucleus and electrons. And nucleus is consisted with proton and neutron. one proton has ( +1.60×10-19C ) as quantity of electric charge, and one electron has ( - 1.60×10-19C ) as quantity of electric charge." So charges are the source of the force.
F = k * q1 q2 / r2 (Coulomb's law)
k : Coulomb constant
q1 : quantity of electric charge for a particle (or matter)
q2 : quantity of electric charge for another
r : distance between q1 and q2
HW6) Find out "k", Coulomb constant and electron's mass.And then write down by MKS unit.
Gravitational force has only attraction force. But Electron-Magnetic force has also repulsive force.
When q1 and q2 are the same charge, the force is repulsive for two particles. And if q1 and q2 are different charge each other, the force is attractive.
atom
Let's look into nucleus. Nucleus includes protons and neutrons. Neutron has no charge.
Anyway in nucleus protons are there together.
Isn't it strange? I said if there are the same charges they repulse each other. Then how can they be together?
We can forecast it in many ways. But the conclusion already made for it is that there is another force.
It's "Strong force". I won't comment for it. Cause it's so difficult academic area. I will skip it.
What we can know now is that "Strong force" is bigger than "Electron-Magnetic force". Otherwise the protons can not stay with each other and they should be scattered because of repulsive forces.
Last fundamental force is "Weak force". When we consider about "Strong force", matter's mass can not be reduced by itself. But in some material, atoms number reduces with respect to time. After "half life" the atoms number decrease into half. It means material's mass reduced by half after half life.
What is the reason? It's because of "Weak force". It's not strong than other fundamental forces in a moment.
But as time goes by weak force become dominant. I will not also explain it deeply.
Let's wrap up in here.
Hope this course would give you good inspiration.
See you next time.
