3.5.1: Normal Force
- Page ID
- 472526
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- Define normal force.
- Explain the relationship between normal force and apparent weight.
Weight (also called force of gravity) is a pervasive force that acts at all times and must be counteracted to keep an object from falling. You definitely notice that you must support the weight of a heavy object by pushing up on it when you hold it stationary, as illustrated in Figure
We must conclude that whatever supports a load, be it animate or not, must supply an upward force equal to the weight of the load, as we assumed in a few of the previous examples. The force supporting a load is perpendicular to the surface of contact between the load and its support, and this force is called a normal force, often indicated with symbol N (Please do not confuse this with the abbreviation for newton, the unit of force, N). The word normal means perpendicular to a surface. The normal force is not always equal to the object's weight, if there are other forces acting on the object, or if the object is accelerating, so that the net force is not zero.
Normal force also goes by another name, apparent weight. This is because all the forces you feel, especially your sensation of weight, are directly attributed to contact forces, such as the normal force. When NASA astronauts are weightlessly floating in the International Space Station, their actual weight (gravitational force on them by the Earth) is not zero, but their apparent weight (sensation of weight due to contact forces) is zero.
Section Summary
- When objects rest on a surface, the surface applies a force to the object that supports the weight of the object. This supporting force acts perpendicular to and away from the surface. It is called a normal force, and it also goes by the name "apparent weight."
Glossary
- normal force
- the force that a surface applies to an object to support the weight of the object; acts perpendicular to the surface on which the object rests
Contributors
Curated from resources found in Introduction to Physics published by OpenStax.
- apparent weight
- sensation of weight due to contact forces; usually the same as normal force