Types of Forces

Applies Force(Fapp)

• An applied force is a force which is applied to an object by another object or by a person.
• If a student is pushing a desk across the classroom, then there is applied force acting on the desk.
• The applied force is the force exerted on the desk by the student.

Normal Force(Fnorm)

The normal force is the support force exerted on an object which is in contact with another stable object.

For example, if a book is resting on a surface, then the surface is exerting an upward force on the book in order to support the weight of the book.

Gravitational Force Also Known as Weight

The gravitational force is the force with which the earth, the moon, or other massive body attracts an object towards itself.

All objects on earth experience a force of gravity which is directed "downward" towards the centre of the earth.

Electrical Force

Forces between electric charges are called electric forces.

These forces sometimes make your hair cling to a plastic comb.

When a charged polythene rod or a rubbed comb is brought very close to a thin stream of running water from a tap, it bends towards the rod due to the electrostatic force.

The charges on the rod attract the unlike charges on the water molecules. So water bends towards charged objects.

Magnetic Force

The attraction and repulsion between the poles of the magnets are due to magnetic force.

Like magnetic poles of a magnet repel and unlike magnetic poles attract each other. Two south poles repel each other as shown in the following figure.

Two north poles also repel each other as shown in the following figure. So they have repulsive magnetic force between like poles.

When the south pole of one magnet is brought close to the north pole of another magnet, they attract each other. So they have attractive magnetic force between unlike poles.

Free-Body Force Diagrams

Free body force diagrams are a useful help to solving problems, a free body force diagram shows all the forces acting on a body.

The size of the arrow tells the magnitude of the force and the direction of the arrow tells us the direction in which the force is acting.

Applications of Free-Body Diagrams

The following free body force diagram shows four forces acting upon the object. The number of forces can be one, two, three or more.

To draw a free body force diagrams, draw a box and add arrows for each existing force in the appropriate direction; label each force arrow according to type of the force.