Define a field in physics. Why are fields useful for describing forces that act at a distance?
Definition:
A field is a region of space where an object experiences a force without touching another object.
Why fields matter:
They explain action at a distance (gravity, electricity, magnetism).
๐ง Memory hook:
No contact, still a force โ thatโs a field.
State one similarity and one difference between gravitational and electric field
Similarity:
Both are fields that act at a distance
Both follow an inverse-square law
Difference:
Gravity only attracts
Electric fields can attract or repel
๐ง Memory hook:
Gravity pulls only โ electricity pushes and pulls.
What do field lines represent? How does the spacing of field lines relate to field strength?
What they show:
Direction of the field
Strength of the field
Spacing meaning:
Close lines = strong field
Spread lines = weak field
๐ง Memory hook:
Crowded lines = strong force.
State the law in words. How does force depend on a) mass? B) distance?
In words:
Every mass attracts every other mass.
Depends on:
Mass โ โ Force โ
Distance โ โ Force โ (squared!)
Formula: F=Gm1m2
———
r(squared)
๐ง Memory hook:
Big masses pull hard, far apart pulls weak.
Explain what is meant by weightlessness. Why do astronauts appear weightless even though gravity is still acting on them?
Meaning:
Weightlessness โ no gravity
It means no normal force.
Astronauts:
They are in free fall around Earth โ gravity still acts!
๐ง Memory hook:
Falling feels weightless.
Define electric field in terms of force and charge. How are electric field and electric force related?
The electric field is defined as the electric force per unit charge:
๐ธ=๐น๐
Electric force is related to electric field by:
๐น=๐๐ธ
This means the electric field determines how strongly a charge will be pushed or pulled.
Explain the relationship between electric potential difference, work done on a charge, and electric fields.
Electric potential difference represents the work done per unit charge to move a charge in an electric field. Electric fields do work on charges by converting electric potential energy into kinetic energy.
ฮ๐=๐๐โ
What determines the direction of magnetic force on a moving charge? What determines when is the magnetic force equal to zero?
The direction of the magnetic force depends on:
-The direction of the chargeโs velocity
-The direction of the magnetic field
-The sign of the charge (right-hand rule)
The magnetic force is zero when:
-The charge is not moving, or
-The charge moves parallel to the magnetic field
Why is gravity negligible compared to electric forces between charged particles like protons and electrons?
Electric force is much stronger than gravity.
Thatโs why:
Atoms donโt collapse
Electricity dominates microscopic physics
๐ง Memory hook:
Gravity is weak โ electricity rules atoms
What is the Schwarzschild radius? What does it represent physically?
Definition:
Radius where escape speed equals speed of light.
Meaning:
If an object shrinks smaller than this โ black hole
๐ง Memory hook:
Light canโt escape โ black hole.
