Lecture7

# Lecture7 - Contact Forces Normal Force It is a contact...

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Contact Forces: Normal Force - It is a contact force. - It is always perpendicular to the contact surface. F N * Are they an action – reaction pair? NO because they act on the same body F N F’ N F’ g F g F g

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Contact Forces: Friction Defined as the force between: • two surfaces in contact (still or in motion) Friction derives from chemical bonding and surface roughness • a medium and a moving object (e.g. air acting on a flying body) STATIC FRICTION KINETIC FRICTION
STATIC FRICTION KINETIC FRICTION It is the force that resist motion. It is always directed // to the two surfaces and perpendicular to the normal force F friction F N F friction friction F N Appears as soon as an object is moving. It opposes to the motion, e.g. it is a vector opposite to the velocity. v F k F N F k F N v F friction //

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|F friction | = μ |F N | S t a i c F r o n Kinetic friction Region where static friction exceeds kinetic friction Friction Resistance Applied Force μ k μ s Experimental observations:
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Lecture7 - Contact Forces Normal Force It is a contact...

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