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Friction & Applying Newton’s 2 nd Law

Learn about friction, its causes, effects on objects in motion, Newton's laws, frictional forces, and how friction impacts the movement of objects. Discover the difference between static and kinetic friction, determining frictional force, and solving examples using Newton's second law.

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Friction & Applying Newton’s 2 nd Law

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  1. Friction & Applying Newton’s 2nd Law System Chapter 6.2

  2. Ff What is Friction? • Friction is a that is parallel to the surfaces of two objects that are in contact with one another that the relative of the two objects.

  3. What causes friction? • Friction is caused by the temporary created between two objects in contact with one another.

  4. Friction • How does friction affect the motion of objects? • It can an object down like the friction between the tires and the road. • It is responsible for the speed of an object like a car. • It is also responsible for objects being able to .

  5. Fground-on-crate FApplied Ffriction System Fgravity Friction ( Objects) • Static Friction: • The that keeps an object from moving. • Since v = ___, a = ___. Fnet = Since the crate is not accelerating, Fnet = __ = Note: As long as the crate does not move, _____ = _____

  6. Fground-on-crate Fapplied Ffriction System Fgravity Friction (Objects in ) • Kinetic Friction: • The that opposes the relative motion of two contacting surfaces that are past one another. • Fnet may or may be ___. Fnet Fnet = Note: If the crate moves at a , then _____ = _____ and Fnet = ___.

  7. FN Ff Determining the Frictional Force (The of Friction, __) • The force of friction (Ff) is proportional to the normal force (FN) and a proportionality constant (___ - pronounced _____) called the of friction. • For static friction: • 0 < Ff, static<sFN • For kinetic friction: • Ff, kinetic = kFN • As per the formula, the greater ___, the greater the . • Note: FN = the () to the on the object. • __ is dimensionless () • _____ > _____

  8. FN  The Force • The force is a force that most often opposes the Earth’s gravitational attraction and is to the that an object rests or is moving on. • For a surface, ____ = ____ = ____. • For a surface that is as seen in the figure below, _____ = ________.

  9. FN Fg  The Normal Force FN cos = adj/hyp Fg ____ = ____ = ____ ____ = ________ = ________

  10. FN Fapplied Ff System Fg Example 2: Determining Friction (Balanced Forces) • Assume that the man in the figure is pushing a 25 kg wooden crate across a wooden floor at a constant speed of 1 m/s. • How much force is exerted on the crate?

  11. +y +x System Diagram the Problem • y-direction: ____ = ____ • x-direction: Fnet = • Since the crate is moving with speed, • a = ___, Fnet = ___, and ______ = ______

  12. State the Known and Unknowns • What is known? • Mass (m) = • Speed = • Acceleration (a) = • k = • What is not known? • Fapplied = ?

  13. Perform Calculations • y-direction: • ___ = ___ = ___ (Note: surface) • x-direction: Since a = ___, Fnet = ___ • Fnet = –

  14. FN Fapplied Ff System Fg Example 3: Determining Friction ( Forces) • Assume that the man in the figure is pushing a 25 kg wooden crate across a wooden floor at a speed of 1 m/s with a force of 73.5 N. • If he doubled the force on the crate, what would the acceleration be?

  15. +y +x System Diagram the Problem y-direction: ____ = ____ x-direction: Since , Fnet =

  16. State the Known and Unknowns • What is known? • Force = • Mass (m) = • Speed = • k = • What is not known? • a ?

  17. Perform Calculations • y-direction: • x-direction: • Fnet = • ma = • a =

  18. Key Ideas • Friction is an that exists between bodies. • Friction is to the and the of ; static or kinetic. • The force required to overcome static friction is than that required to overcome kinetic friction.

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