Normal force and contact force | Forces and Newton's laws of motion | Physics | Khan Academy | Summary and Q&A

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June 18, 2011
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Normal force and contact force | Forces and Newton's laws of motion | Physics | Khan Academy

TL;DR

Newton's First Law states that an object at rest or in motion will remain that way unless acted upon by a net force. The normal force, provided by a surface, balances out the force of gravity to keep objects stationary or in constant motion.

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Q: What does Newton's First Law of Motion state?

Newton's First Law states that objects at rest will remain at rest, and objects in motion will continue moving at a constant velocity unless acted upon by an unbalanced force.

Q: What force counteracts the force of gravity to keep objects from falling?

The normal force, provided by a supporting surface, counteracts the force of gravity and prevents objects from accelerating downward.

Q: Why does a block of ice on a frozen pond experience a normal force?

The normal force is the result of electromagnetic repulsion between the atoms or molecules of the block of ice and the surface of the pond, preventing the block from sinking further.

Q: How does the normal force play a role in objects on inclined surfaces?

The normal force acts perpendicular to the surface and helps balance out the force component pushing the object down the incline, influencing the object's motion.

Summary & Key Takeaways

• Newton's First Law states that an object will maintain its state of rest or constant velocity unless acted upon by a net force.

• The force of gravity, exerted on objects near Earth's surface, pulls them downwards with a force equal to mass multiplied by the gravitational field strength (9.8 m/s^2).

• The normal force is the upward force exerted by a surface, which counteracts the force of gravity, allowing objects to stay stationary or move with a constant velocity.