Contact and non-contact forces

This section introduces fundamental concepts in physics, focusing on the nature of forces. Understanding these concepts is essential for describing motion, interactions, and the effects of forces on objects.

What is a force

• A force is a push or pull that arises from the interaction between two objects.

• Force is a vector quantity, meaning it has both magnitude and direction.

Contact forces

• Forces that arise when two objects are physically touching.

• Examples:

  1. Friction: A force resisting motion between two surfaces in contact.

  2. Air Resistance: The force of air acting against a moving object (e.g., a falling parachute).

  3. Tension: A pulling force transmitted through a rope or string.

  4. Normal Contact Force: The perpendicular force exerted by a surface on an object resting on it.

Non-contact forces

• Forces that occur even when objects are physically separated.

• Examples:

  1. Gravitational Force: The attraction between two masses (e.g., the Earth and the Moon).

  2. Electrostatic Force: The force between charged particles (e.g., the attraction between a positively charged object and a negatively charged object).

  3. Magnetic Force: The attraction or repulsion between magnetic materials.

Interactions between objects

• Forces Always Come in Pairs: According to Newton’s Third Law, every force exerted by one object on another results in an equal and opposite force on the first object. For example:

• A book resting on a table exerts a downward force due to gravity, while the table exerts an equal upward force (normal contact force).

Interactions between objects

Force Representation Using Vectors

• Forces are represented as arrows where:

  • Magnitude is shown by the arrow’s length.

  • Direction indicates where the force is acting.

  • Example: The force of gravity acting on an object can be represented by a downward arrow, while a supporting normal force is represented by an upward arrow.

Key skills and application