16. Contact & Non-contact Forces

1. What is a Force?

• Definition: A force is a push or pull that acts on an object due to its interaction with another object.

• Measurement: Forces are measured in Newtons (N).

• Vector Quantity: Forces have both magnitude (size) and direction. For example, "5 Newtons to the right."

2. Contact Forces

Contact forces occur when two objects are physically touching.

• Friction: Acts between two surfaces sliding (or trying to slide) across each other.

• Air Resistance: A type of friction that occurs when an object moves through air particles.

• Tension: The pulling force exerted through a rope, string, or cable when it is pulled tight.

• Normal Contact Force (Reaction Force): An upward force exerted by a surface that supports the weight of an object resting on it. It acts at a right angle (normal) to the surface.

3. Non-contact Forces

Non-contact forces can act through empty space; the objects do not need to be touching.

• Gravitational Force: An attractive force between any two objects with mass (e.g., the Earth pulling on you).

• Magnetic Force: Can be attractive (pulling together) or repulsive (pushing apart), acting between magnets or magnetic materials.

• Electrostatic Force: Acts between charged objects; can also be attractive or repulsive.

Key Characteristics of Non-contact Forces

• Fields: These forces are often described as "fields of influence" around an object.

• Distance: The strength of a non-contact force decreases as the distance between the two objects increases.

4. Summary Table