What is friction?
Friction is the resistance of motion when one object rubs against another. Anytime two objects rub against each other, they cause friction. Friction works against the motion and acts in the opposite direction.
Friction and Energy
When one object is sliding on another it starts to slow down due to friction. This means it loses energy. However, the energy doesn't disappear it changes from moving energy (also call kinetic energy) to heat energy. This is why we rub our hands together when its cold. By rubbing them we generate friction and, therefore, heat.
The force F of friction pushes back on the block.
In some cases we want to prevent friction so it's easier to move. A good example of this is a ball or wheel. They roll to help reduce friction. Another way to reduce friction is with a lubricant like grease or oil. Machines and engines use grease and oil to reduce friction and wear so they can last longer. A third way to reduce friction is with less surface area. This is how ice skates work. A thin blade allows for little friction between the skate and the ice. Ice skates also use lubricant in that the ice melts beneath the weight of the blade using water to allow for the skates to slide.
Friction is also a great help to us. After all, we would all just be sliding around everywhere if there wasn't friction to keep us steady. Friction is also used in car brakes, when we walk or climb a hill, in sandpaper, making a fire, and more.
Experiment with Friction
Different types of surfaces create different amount of friction. Some materials are much smoother than others. Take three flat objects with different type of surfaces. Set them on one end of a tray and slowly lift it. The item with the least friction will start to slide first. There are 3 main factors that will influence the amount of friction 1) the roughness of the surfaces 2) the weight of the object 3) the surface...