The definition of force

The activity of pulling or pushing is that of giving force. Therefore, force means to pull or push. The force unit in MKS is newton (N) and cgs is dyne.

1. Contact force and long range force

What is the meaning of contact force and long range force? Muscular force is a contact force because the work point of muscular force is direectly in contact with the body. The friction between a tyre and a road is also a contact force, because there is a contact occurred between the tyre and the road.

An apple can fall to the earth, because it is pulled by the earth gravitation force. Meanwhile, nails can be pulled by magnet because of the magnetic force. Gravitational force and magnetic force are long range forces, because the forces can happen although they do not contact to each road.

From the explanation above, it can be concluded:

Contact force is a force that works on body,and there is a contact occurred between the force and the body. While long range force is a force that works on a body and there is no contact occurred between the force and the body.

2. The Efect of Force on Body
The force working on a body effects the condition of the body. If a force exerts on a body, it will couse some changes.

• The rest-body will move. for example, a table that is pushed.
• The moving body will be at rest. For example, a ball which is caught.
• The form and size of the body will change. For example, a spring which is pulled.

3. Measuring Force
The instrument used to measure the magnitude of force is dynamometer. The magnitude of measured force is shown by pointer on dynamometer.

4. Magnitude and Direction of force
Force has magnitude  and direction. The force direction is drawn by using a vector diagram like an arrow, with the origin point A and the edge B. The length of AB shows the force magnitude; while the arrow shows the force direction.