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Friction & Applying Newton’s 2 nd Law

Friction & Applying Newton’s 2 nd Law. System. Chapter 6.2. F f. 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. What causes friction?.

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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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