The normal force keeps solid objects apart due to the electromagnetic forces of atoms repelling each other. It is perpendicular to the surface causing it and is important in calculating friction between solid objects. It cancels out the gravitational force on level ground but not on a hill. When two objects collide, momentum is responsible for the normal force. It is important in determining static and kinetic friction.
The normal force is responsible for keeping two objects physically apart in space. Without it, solid objects would fuse together without any resistance. It is basically caused by the electrical forces of many atoms repelling each other. Objects are typically brought into contact by gravitational force or collision. This force is an important concept in classical mechanics for calculating friction between solid objects.
It is commonly said that there are four fundamental forces of nature: the gravitational, electromagnetic, weak nuclear and strong nuclear forces. The normal force is actually a set of electromagnetic forces. At the atomic level, two objects resist being smashed together because the electrons of one object resist those of the other. Electrons have a negative charge, so two electrons will tend to repel each other when they are close together. When many atoms collectively behave this way, the result is the normal force.
This force is always directed perpendicular to the surface causing it. When a car is on level ground, the normal force is vertical and will exactly cancel out the gravitational force. This is why a flat car will not accelerate uphill or downhill. The force on a car going down a hill, however, forms a right angle with the road, even though the gravitational force is still directed vertically. Since these forces no longer exactly cancel each other out, a car will accelerate downhill even if no gas is used.
Another possible situation involving force is when two objects collide. When this happens, it is not gravity but momentum that is responsible for the normal force. Newton’s first law states that moving objects will stay in motion unless acted upon by an external force. So colliding objects must exert forces on each other for them to change speed. In fact, this is exactly what they do: the forces they exert on each other are just enough to make them move at their final velocities.
In classical mechanics, the normal force is important in determining static and kinetic friction. These refer to friction between solid objects, such as a box sliding across the floor. This type of friction is proportional to the normal forces. In everyday cases, the weight of an object is what is responsible for its normal strength. That’s why it’s harder to push a heavy box than a lighter one.
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