We cannot see force, but we know that it is there because we observe its effect. The above illustrations show that force can move a stationary object.
Sometimes the effect of force is not visible. When you push against a wall, you are using force, but the effect cannot be seen. But when there is an egg between your hand and the wall, you will be able to observe that you have exerted force quite plainly!
For instance, a force can change the kinematics of a body (a force can stop or move a body, changing the speed of the body, by increasing or decreasing it, or the force can change the direction of motion of that body).
Also, a force can change the original shape and size of a body.
As conclusion, any kind of action, of pull or push type, that has as result the changing of velocity of the body, is called force.
Force has many applications in our daily life as:
1-Games depend on the effect of the force as
- Pulling rope game
2-balloon and rocket game
- Moving of heavy objects and their rising
- Some technological applications
It is also true that a force can act on a body without any visible effect. For example, when a boulder rests on the ground, gravity is acting upon it but no effect is seen because the normal force is also acting on it to keep it in equilibrium.
Sometimes, a force can act on an object but be too small to change anything about that body. An example would be a grasshopper jumping off that boulder -- it would exert force but the force would be too small to overcome the other forces acting on the boulder.