Basic Concepts
In a nutshell: Forces cause changes in motion, explained by Newton's three laws.
## The Rules Behind Motion
Once you know how things move, it's time to ask *why*. Newton's Laws explain what causes motion—forces!
### Newton's Three Laws
1. **Inertia**: Objects keep doing what they're doing unless something (a force) changes that.
2. **F=ma**: The net force on an object equals its mass times its acceleration.
3. **Action-Reaction**: For every action, there's an equal and opposite reaction.
### Types of Forces
- Gravity pulls you down.
- Friction slows you down.
- Tension, normal force, and others support, stretch, or compress.
### Everyday Physics
These laws explain why seatbelts are crucial (inertia!), why you push harder to move a heavier box (F=ma), and why jumping off a boat pushes the boat back.
F = ma
Examples
- A skateboarder pushes off the ground and accelerates forward.
- A book resting on a table experiences gravity and a normal force.
Key terms
- Force
- A push or pull that changes an object's motion.
- Friction
- A force that resists motion between two surfaces.