Friction is a force that acts between two objects in contact with each other. Friction acts to resist movement of objects. The amount of friction between objects depends on the material the objects are made of. For example, a sled has less friction on ice than it does on concrete because ice is a smoother material. Friction can also occur between objects and the air. This is called air resistance. Friction acts in the opposite direction as the object is moving. Friction can have positive and negative impacts on us at times. Friction is necessary to keep us from falling all the time, it keeps our tires on the road, friction can produce heat and it also allows the breaks on a roller coaster to work so you stay on the tracks! It can sometimes have negative impacts as well. Think of times you have had to walk against the wind outside or had to pull a heavy box across the floor. Friction makes you use more force to do certain tasks.