Physics Lesson 10/28

Physics Lesson 10/28

Open Ended

Chop Wood Carry Water

Review of Kinetic Friction

Static Friction

• The maximum static friction force relates to the normal force in a similar way as the kinetic friction force.

• Remember, the static friction force acts in response to a force trying to cause a stationary object to move.

• If there is no such force on the object, the static friction force is 0.

Static Friction

• If there is a force trying to cause motion, the static friction force will increase up to a maximum value before it is overcome and motion starts.

Static Friction

•  $F_{f,\ static}\ \le\ \mu_sF_N$  Th

• In the equation for the maximum static friction force,  $\mu_s$  is the coefficient of static friction between two surfaces.

• The maximum static friction force that must be overcome before motion can begin is $\mu_sF_N$  .

Fill in the Blank

Example Problem - You push a 25.0 kg wooden box across a wooden floor at a constant speed of 1.0 m/s. The coefficient of kinetic friction is 0.20. How large is the force you exert on the box?

Practice Problems

Open Ended

Exit Ticket - As the normal force increases, what happens to the friction force?