General Physics
Mechanics, Thermodynamics, and Electromagnetism
In This Lesson
Kinematics
Kinematics is the study of motion without considering the forces that cause it.
Key Definitions
- Displacement (x): Change in position (vector)
- Velocity (v): Rate of change of displacement
- Acceleration (a): Rate of change of velocity
- Speed: Magnitude of velocity (scalar)
Kinematic Equations (Constant Acceleration)
- v = v₀ + at
- x = v₀t + ½at²
- v² = v₀² + 2ax
- x = ½(v + v₀)t
Where: v = final velocity, v₀ = initial velocity, a = acceleration, t = time, x = displacement
Free Fall
- Acceleration due to gravity: g = 9.8 m/s² (downward)
- Use kinematic equations with a = -g (taking up as positive)
- At maximum height, v = 0
Newton's Laws of Motion
First Law (Law of Inertia)
An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net external force.
Second Law (F = ma)
The acceleration of an object is directly proportional to the net force and inversely proportional to its mass.
F = ma
Force (N) = mass (kg) × acceleration (m/s²)
Third Law (Action-Reaction)
For every action, there is an equal and opposite reaction. Forces always come in pairs acting on different objects.
Common Forces
- Weight: W = mg (gravitational force)
- Normal Force: Perpendicular to surface
- Friction: f = μN (μ = coefficient of friction)
- Tension: Force through rope/string
Energy & Work
Work
W = Fd cos θ
Work is done when force causes displacement. Unit: Joules (J)
Power
P = W/t = Fv
Rate at which work is done. Unit: Watts (W)
Kinetic Energy
KE = ½mv²
Energy of motion. Depends on mass and velocity.
Potential Energy
PE = mgh (gravitational)
PE = ½kx² (elastic/spring)
Stored energy due to position or configuration.
Conservation of Energy
KE₁ + PE₁ = KE₂ + PE₂
Total mechanical energy is conserved in the absence of non-conservative forces (like friction).
Waves & Sound
Wave Properties
- Wavelength (λ): Distance between consecutive crests
- Frequency (f): Number of waves per second (Hz)
- Amplitude (A): Maximum displacement from rest
- Period (T): Time for one complete wave (T = 1/f)
Wave Equation
v = fλ
Wave speed = frequency × wavelength
Transverse Waves
Oscillation perpendicular to wave direction (e.g., light, water surface)
Longitudinal Waves
Oscillation parallel to wave direction (e.g., sound waves)
Electricity & Magnetism
Coulomb's Law
F = k(q₁q₂)/r²
Force between two charges. k = 9 × 10⁹ N·m²/C²
Ohm's Law
V = IR
Voltage (V) = Current (A) × Resistance (Ω)
Electric Power
- P = IV
- P = I²R
- P = V²/R
Circuits
Series:
- R_total = R₁ + R₂ + ...
- Same current through all
Parallel:
- 1/R_total = 1/R₁ + 1/R₂ + ...
- Same voltage across all