Describe a mechanical action
What is a force?
What is a mechanical action?
A mechanical action is what happens when an object (or a person) acts on another object. This action can:
- deform the object (crush, stretch, bend),
- set a stationary object in motion,
- stop or slow down a moving object,
- change the path of a moving object.
We then say that a force is acting on the object.
Two main families of forces
| Type of force | Description | Example |
|---|---|---|
| Contact force | The object must be touched to act on it | Pushing a cart, pulling a rope |
| Force at a distance | No contact is necessary | Weight (gravity), magnets |
Concrete examples
- When you kick a ball, your foot exerts a contact force on the ball: it is set in motion.
- When you let go of an object, the Earth exerts a force at a distance on it (its weight): it falls.
- A magnet attracts a paperclip without touching it: this is a force at a distance.
Effects of a force
A force can have several effects, sometimes combined:
- Effect on motion (starting, accelerating, slowing down, deflecting).
- Effect on the shape of the object (deformation).
Classic pitfall to avoid
Don't confuse force and speed. A force is not a motion, it is what can cause or change a motion (or a deformation). An object can also remain stationary even though several forces act on it, if they cancel each other out (we will see this in the next lesson).