Force | Contact or action at a distance | Example |
---|---|---|
Frictional force | Contact | Friction results from the two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces. The friction force opposes the motion of the object. |
Gravitational force | Action at a distance | The force of gravity is the force at which the earth, moon, or other massively large object attracts another object towards itself. |
Applied force | Contact | If a person is pushing a desk across the room, then there is an applied force acting upon the object. The applied force is the force exerted on the desk by the person. |
Electrical repulsion force | Action at a distance | Leaves of gold in an electroscope repel each other and part when they get changed. The repulsion arises due to the fact that the leaves acquire same charge. |
Air resistance | Contact | The air resistance is actually frictional force which acts upon objects as they travel through the air. Air resistance always opposes the motion of the object. This force generally has negligible magnitude. Air resistance is encountered significantly for objects which travel at high speeds or for objects with large surface areas. |
Magnetic attraction | Action at a distance | Two bar magnets attract each other when their opposite poles (north and south or vice versa) are facing each other. |
Nuclear force | Action at a distance | A nucleus of an atom consists of positively charged protons. These stay together inside the volume of the nucleus due to strong nuclear forces. Nuclear force is atleast a hundred times stronger than electrical repulsive force. |