Welcome to 9th Grade Physics
In 9th grade physics, students study the foundations of mechanics. Topics include motion, speed, acceleration, force, Newton’s Laws, work, energy, and power.
This course builds the scientific thinking needed for advanced physics in later grades.
The 3 laws of motion
- Speed is how fast something is moving.
- Acceleration is how quickly speed changes.
- Force causes objects to move or change motion.
- Energy is the ability to do work.
- First Law: An object at rest stays at rest, and an object in motion stays in motion unless acted on by a force.
- Second Law: Force equals mass times acceleration (F = ma).
- Third Law: For every action, there is an equal and opposite reaction.
Work and Energy
Work is the transfer of energy when a force moves an object. The formula is W = F × d where W is work in joules (J), F is force in newtons (N), and d is displacement in meters (m).
- Kinetic energy: Ek = 1/2 m v²
- Potential energy (gravity): Ep = m g h
Waves & Sound
Waves transfer energy without transferring matter. Key properties:
- Amplitude — wave height
- Wavelength (λ) — distance between peaks
- Frequency (f) — cycles per second (Hz)
- Wave speed: v = f × λ