Friction applying newton s 2 nd law
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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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Friction applying newton s 2 nd law

Friction & Applying Newton’s 2nd Law

System

Chapter 6.2


What is friction

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.


What causes friction

What causes friction?

  • Friction is caused by the temporary created between two objects in contact with one another.


Friction

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

      .


Friction objects

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, _____ = _____


Friction objects in

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 = ___.


Determining the frictional force the of friction

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 ()

  • _____ > _____


The force

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, _____ = ________.


The normal force

FN

Fg

The Normal Force

FN

cos = adj/hyp

Fg

____ = ____ = ____

____ = ________ = ________


Example 2 determining friction balanced forces

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?


Diagram the problem

+y

+x

System

Diagram the Problem

  • y-direction: ____ = ____

  • x-direction: Fnet =

    • Since the crate is moving with speed,

    • a = ___, Fnet = ___, and ______ = ______


State the known and unknowns

State the Known and Unknowns

  • What is known?

    • Mass (m) =

    • Speed =

    • Acceleration (a) =

    • k =

  • What is not known?

    • Fapplied = ?


Perform calculations

Perform Calculations

  • y-direction:

    • ___ = ___ = ___(Note: surface)

  • x-direction: Since a = ___, Fnet = ___

    • Fnet = –


Example 3 determining friction forces

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?


Diagram the problem1

+y

+x

System

Diagram the Problem

y-direction: ____ = ____

x-direction: Since , Fnet =


State the known and unknowns1

State the Known and Unknowns

  • What is known?

    • Force =

    • Mass (m) =

    • Speed =

    • k =

  • What is not known?

    • a ?


Perform calculations1

Perform Calculations

  • y-direction:

  • x-direction:

    • Fnet =

    • ma =

    • a =


Key ideas

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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