What Causes Friction?
•Friction is the force that opposes the motion between two
surfaces that touch.
• The surface of any object is rough.
• Even an object that feels smooth is covered with tiny hills
and valleys.
• The contact between the hills and valleys of two surfaces
causes them to stick, resulting in friction.
3.
• The amountof friction depends on:
– Roughness of the surfaces (type of surface)
– Motion of the surfaces
– Force pushing the surfaces together
What Causes Friction?
6.
• Try rubbingyour hands together
at a quick pace.. You should feel
heat!
• Friction between surfaces
produces heat
• Friction causes the molecules on
the surface of your hands to move
faster.
• As the molecules move faster, the
temperature of the object
increases.
Friction and Heat
7.
• Kinetic frictionoccurs when force is applied to an
object and the object moves.
• Examples:
Sliding Friction: pushing an object across a surface
Rolling Friction: between wheels and a surface
Fluid Friction: opposes the motion of objects
traveling through a fluid (air or water)
Types of Friction
8.
Fluid Friction: AirResistance
• Most objects falling through air experience a
type of fluid friction called air resistance.
• Air resistance is not the same for all objects.
• The greater the surface area of the object the
greater the air resistance.
• However, since the elephant has more mass, it
has more downward force of gravity and falls
faster.
9.
• Some shapes,known as streamlined
shapes, cause less air resistance than
others. Aeroplanes and cars are
streamlined, so that they move through
the air as easily as possible.
10.
• Static frictionoccurs when force applied
to an object does not cause the object to
move.
Types of Friction
11.
• Friction canbe a useful force because it
prevents our shoes slipping on the pavement
when we walk and stops car tires skidding on
the road.
12.
• Ice causesvery little friction, which is why it
is easy to slip on an icy day. But this is a good
thing for ice skating and sledding!
13.
• To reducethe amount of friction, apply a lubricant
between two surfaces.
• Motor oil, wax, and grease are examples.
• Friction can also be reduced by rolling, rather than
pushing, an object.
Reducing Friction
14.
• Friction increasesas surfaces are made
rougher.
• Friction increases when the force between
two objects is increased.
Increasing Friction
