# More on Normal force (shoe on floor) | Physics | Khan Academy | Summary and Q&A

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July 29, 2016
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More on Normal force (shoe on floor) | Physics | Khan Academy

## TL;DR

Normal force is a contact force that only exists when two surfaces are in contact, and it is not always equal to the weight of an object.

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### Q: When does the normal force exist?

The normal force exists when two surfaces are in contact, such as a shoe on the floor or a shoe on a wall. It is a contact force that prevents penetration between the object and the surface.

### Q: What happens if an object is not in contact with any surface?

If an object is not in contact with any surface, there is no normal force acting on it. In this case, only the gravitational force would act on the object.

### Q: Is the normal force always equal to the weight of an object?

The normal force is not always equal to the weight of an object. It is only equal to the weight when there are no other forces acting on the object and the object is on a level surface.

### Q: Can the normal force change with additional forces?

Yes, the magnitude of the normal force can change with additional forces. If a downward force is applied to the object, the normal force will increase. If an upward force is applied, the normal force will decrease.

## Summary & Key Takeaways

• Normal force is a contact force that exists when two surfaces are in contact, whether it's a shoe on the floor or a shoe on a wall.

• Normal force is not present when an object is not in contact with a surface, such as when a shoe is falling through the air.

• The magnitude of the normal force can change depending on additional forces acting on the object, such as pushing down or pulling up on the object.