Friction Air Resistance Friction Force that opposes the

Friction & Air Resistance

Friction • Force that opposes the sliding motion of two surfaces that are touching each other • Direct contact force

• When two surfaces are in contact, welding or sticking occurs where the bumps from each surface touch • Amount of friction depends on: • Kind of surface • Force pressing surfaces together • Greater the force, greater the microwelds

Static friction • Frictional force that prevents two surfaces from sliding past each other. • Unless the force acted on the object is great enough to break the microwelds between the surfaces, the object will not move

Air resistance • Friction-like force that opposes motion of objects that move through air • Causes objects to fall with different accelerations and speeds

Air Resistance • Depends on the size, shape and speed of the object • Not its’ mass!!! • If 2 different massed objects were to be dropped at same time without air resistance they would hit ground at same time

Practice Question • What letter represents a feather and apple dropped at the same time in real life? • What letter represents a feather and apple in space or a vacuum where there is no air resistance?

Terminal velocity • The faster something falls the greater the force of air resistance • Eventually reach terminal velocity (maximum velocity) • two forces (air resistance and gravity) cancel each other out • Net Force = 0 N • Causes the object to fall at a constant speed (acceleration= 0 m/s 2)