S2.6 Normal contact force
[A] About the force
The normal contact force FN is the repulsive force of interaction between two surfaces in contact, acting at right angles to the surfaces, and inhibiting closer contact.
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[B] Example problem
Two bodies are free to move on a smooth horizontal surface under the action of a horizontal force of magnitude FA. |
Determine the acceleration and the normal contact force between them.
Solution
Reveal
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Solution
- Let a be the acceleration to right (same for both bodies)
- Choose a system comprising both masses.
Apply 2nd law:
FA=(m1+m2)aimplying - Choose a system comprising 2nd mass alone.
Apply 2nd law: FN=m2aso Eliminate a:
Hence
Results
acceleration:
![\[ a = \frac{F_A}{m_1 +m_2} \]](mastermathpng-4.png)
![\[ F_N= F_A \frac{m_2}{m_1 +m_2} \]](mastermathpng-5.png)
Check It!
- Are the units OK?
- Does it make sense?
Learning Resources
![]() | HRW Chapter 5.7,5.9 |
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