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Friction & Applying Newton’s 2 nd LawPowerPoint Presentation

Friction & Applying Newton’s 2 nd Law

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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?

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

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

.

- It can an object down

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, _____ = _____

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 = ___.

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 ()
- _____ > _____

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, _____ = ________.

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?

+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

- What is known?
- Mass (m) =
- Speed =
- Acceleration (a) =
- k =

- What is not known?
- Fapplied = ?

Perform Calculations

- y-direction:
- ___ = ___ = ___ (Note: surface)

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

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?

State the Known and Unknowns

- What is known?
- Force =
- Mass (m) =
- Speed =
- k =

- What is not known?
- a ?

Perform Calculations

- y-direction:
- x-direction:
- Fnet =
- ma =
- a =

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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