Overview
This lecture explains what forces are, distinguishes between contact and non-contact forces, and provides examples of each type.
What is a Force?
- A force is a push or pull acting on an object due to its interaction with another object.
- Forces are measured in newtons (N).
- Forces have both magnitude (size) and direction, making them vector quantities.
Contact Forces
- Contact forces act when two objects are physically touching.
- Friction is a contact force; it requires surfaces to touch for resistance.
- Air resistance is a contact force; objects must contact air particles to experience it.
- Tension is a contact force transmitted through a rope, string, or cable when pulled tight.
- The normal contact force (reaction force) is the upward force exerted by a surface to support the weight of an object.
Non-Contact Forces
- Non-contact forces act at a distance without objects touching.
- Gravitational force is an attraction between objects with mass (e.g., Earth and you).
- Magnetic force occurs between magnets and can be attractive or repulsive.
- Electrostatic force occurs between charged objects and can be attractive or repulsive.
- The strength of non-contact forces decreases as distance between objects increases.
Key Terms & Definitions
- Force — a push or pull on an object from another object.
- Vector quantity — a value with both magnitude and direction.
- Contact force — force that acts when objects are touching.
- Friction — contact force resisting motion between surfaces.
- Air resistance — contact force due to air particles.
- Tension — contact force through a stretched material.
- Normal contact force — upward support force from a surface.
- Non-contact force — force that acts without objects touching.
- Gravitational force — attraction between masses.
- Magnetic force — interaction between magnetic poles.
- Electrostatic force — force between charged objects.
Action Items / Next Steps
- Review examples of forces in daily life.
- Prepare to study magnetic and electrostatic forces in more detail in future lectures.