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# Static Friction - PowerPoint PPT Presentation

Static Friction. Holding in Place. Objects on an incline will often stay put. There must be a force that holds the object in place. Static friction is from the contact of resting objects. Force holds up to a certain point Force is based on the type of contact (rough, smooth)

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## PowerPoint Slideshow about ' Static Friction' - deacon-rosario

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Presentation Transcript

### Static Friction

• Objects on an incline will often stay put.

• There must be a force that holds the object in place.

• Static friction is from the contact of resting objects.

• Force holds up to a certain point

• Force is based on the type of contact (rough, smooth)

• Maximum force is proportional to the pressing force of the object (normal force)

• The approximate formula for static friction is:

ms is the coefficient of static friction

• This is an inequality.

• The force of static friction is generally less than the coefficient times the normal force

q

Starting Motion

• If Ffr < msFN = msmg cosq, then the block will hold.

• At equality the block just begins to move.

Forces balance on mass 1

Tension is equal on the rope

Forces balance on mass 2

m1

m2

Measuring Friction: Pulley

FT

Frope

FT

Frope

The pulley determines the coefficient of friction through the ratio of masses.

m1

m2

Coefficient of Friction: Pulley

One component of gravity balances the normal force

The other component of gravity balances friction

m

q

Measuring Friction: Incline

The incline determines the coefficient of friction through the tangent of the angle.

m

q

Coefficient of Friction: Incline

Normal Force and Friction the tangent of the angle.

• Static friction depends on both the normal force and on the coefficient of friction.

• To reduce friction requires reducing one of those factors.

• Reduce normal force by lightening the load