1. How does friction affect motion?

2. 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 amount of friction depends on:
What Causes Friction?
The amount of friction depends on:
Roughness of the surfaces (type of surface)
Motion of the surfaces
Force pushing the surfaces together

6. Friction and Heat
Try rubbing your 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.

7. Types of Friction
Kinetic friction occurs 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)

8. Fluid Friction: Air Resistance
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. Air Resistance
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. Types of Friction
Static friction occurs when force applied to an object does not cause the object to move.

11. Useful Friction and Reducing Friction.
Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tires skidding on the road.

12. Useful Friction and Reducing Friction.
Ice causes very 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. Reducing Friction
To reduce the 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.

14. Increasing Friction Friction increases as surfaces are made rougher.
Friction increases when the force between two objects is increased.