1
PHY131H1S – Class 10
Today:
• Friction, Drag
• Rolling without
slipping
• Examples of Newton’s
Second Law
Problem Set 3 on
MasteringPhysics due
Friday at 11:59PM
Microscopic bumps and holes
crash into each other, causing
a frictional force.
Static Friction
The box is in static
equilibrium, so the static
friction must exactly balance
the pushing force:
Static Friction
There’s clearly a limit to how big fscan get. If you
push hard enough, the object slips and starts to
move. In other words, the static friction force has a
maximum possible size fsmax
.
•An object remains at rest as long as fs< fsmax
.
•The object slips when fs= fsmax
.
•A static friction force fs> fsmaxis not
physically possible.
where the proportionality constant μsis called
the coefficient of static friction.
A wooden block weighs 100 N, and is sitting
stationary on a smooth horizontal concrete
surface. The coefficient of static friction between
wood and concrete is 0.2. A 5 N horizontal force
is applied to the block, pushing toward the right.
What is the force of static friction of the concrete
on the block?
A. 100 N, to the left
B. 20 N, to the left
C. 5 N, to the left
D. 20 N, to the right
E. 5 N, to the right
A wooden block weighs 100 N, and is sitting
stationary on a smooth horizontal concrete
surface. The coefficient of static friction between
wood and concrete is 0.2. A horizontal force is
applied to the block, pushing toward the right.
What is the maximum pushing force you can
apply and have the block remain stationary?
A. 200 N
B. 100 N
C. 20 N
D. 10 N
E. 5 N
