1.6 - Contact & Non-Contact Forces

Forces can be contact or non-contact

• A force is a push or a pull on an object, caused by an interaction with another object.
• Every force has a size and a direction.

Contact forces

A contact force only acts when two objects are touching.

• Friction - Acts between two surfaces that are sliding, or trying to slide, past each other.
• Drag - Acts on an object moving through a fluid. Drag in air is called air resistance.
• Tension - The pull in a stretched rope, cable or string.
• Normal contact force - The push that two touching surfaces exert on each other, at right angles to the surfaces.
• Upthrust - The upward push a fluid exerts on an object placed in it.

Non-contact forces

A non-contact force can act even when the objects are not touching. These forces are caused by fields interacting.

• Gravitational force - The attraction between any two masses (such as the Earth and the Sun).
• Electrostatic force - The attraction or repulsion between charged objects (like charges repel, opposite charges attract).
• Magnetic force - The attraction or repulsion between magnetic objects.