Physics
The Forces
Introduction
11
⚡ Quick Summary
Forces are what make things move, stop, or change direction. They're the pushes and pulls of the universe!
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Forces are interactions that can cause a change in an object's motion. They are vector quantities, having both magnitude and direction.
Gravitational Force
11
⚡ Quick Summary
Gravity pulls everything towards everything else. It's why we stay on the ground and why the planets orbit the sun.
F = Gm1m2/r^2
Gravitational force is an attractive force between any two objects with mass. It is described by Newton's Law of Universal Gravitation.
Electromagnetic (EM) Force
11
⚡ Quick Summary
The EM force is what holds atoms together and causes electricity and magnetism. It's much stronger than gravity!
F = k q1q2 / r^2 (Coulomb's Law)
Electromagnetic force is the force between charged particles. It is responsible for many phenomena, including electricity, magnetism, and the structure of matter.
Nuclear Forces
11
⚡ Quick Summary
Nuclear forces hold the nucleus of an atom together. They're the strongest forces, but they only act over very short distances.
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Nuclear forces are the forces that hold the protons and neutrons together in the nucleus of an atom. They are very strong but act over very short distances.
Weak Forces
11
⚡ Quick Summary
Weak forces are involved in radioactive decay. They're weaker than nuclear forces, but still important!
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Weak forces are responsible for certain types of radioactive decay, such as beta decay.
Scope of Classical Physics
11
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Classical physics deals with things that are big enough to see and move at speeds much slower than light. It's still useful for many everyday situations!
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Classical physics encompasses mechanics, thermodynamics, electromagnetism, and optics. It is applicable to macroscopic objects moving at speeds much less than the speed of light.
Newton's Third Law of Motion
Class 11
⚡ Quick Summary
For every action, there's an equal and opposite reaction. If you push on a wall, the wall pushes back on you with the same amount of force. These forces always act on *different* objects.
F<sub>A on B</sub> = - F<sub>B on A</sub>
- If body A exerts a force F on body B, then body B exerts a force -F on body A.
- These two forces (F and -F) are called an action-reaction pair. It doesn't matter which one you call the 'action' and which you call the 'reaction'.
- Action-reaction forces act along the line joining the two bodies.
Gravitational Force
Class 11
⚡ Quick Summary
Gravity is the force of attraction between any two objects with mass. The bigger the masses and the closer they are, the stronger the gravitational force.
F = G * (m1 * m2) / r^2 , where G = 6.67 x 10^-11 N-m^2/kg^2
- Any two bodies attract each other by virtue of their masses.
- The gravitational force between two point masses is given by a formula involving their masses and the distance between them.
- For extended bodies, you need to consider the gravitational force between each particle in one body and each particle in the other body, and then add up all these forces vectorially.