answ:1] use oil,replace sliding with rolling

2)yes for both

3)caused by air

So how could we reduce this level of friction ? We could add a lubricant such as oil between the two surfaces, the coefficient of friction between two well-oiled metallic surfaces is about 0.01.

Can you think of other ways friction can be reduced ?

One way is replace sliding with rolling. We can use ball-bearings, this greatly reduces friction and gives a coefficient of friction about 0.002.

Other ways include the use of air cushions (e.g. hovercrafts) and by streamlining (car design, cyclists helmets etc.).

Another measure of friction is the angle of friction. To measure this we would place our object (say a block of wood) onto a surface and slowly tilt the surface until the block of wood started to move under gravity. By measure the angle of tilt we determine the angle of friction.

Have you ever tried to push a car ? When you start to push it is difficult to get the car moving but once the car is moving it is easier to keep it moving. This gives another clue about friction. The degree of friction between two object is greatest when they are at rest (this is called the static friction or friction at rest). Once the object is moving the level of friction is reduced (this is called the kinetic friction or friction of motion).

We have seen that friction acts to resist movement and that engineers have evolved methods to reduce the effect of friction. I have indicated that reducing the level of friction improves the efficiency of a motor (or machine), this is because we make better use of the energy we put into the machine (less energy is lost overcoming friction). But what happens to the energy that is “lost” ? We can get some idea of what happens if we rub our hands together very quickly. There is friction between the palms of hands and we put in energy to overcome this friction this energy is converted into heat. This can be useful if our hands are cold but is not useful in machines, the heat is lost to the surroundings and is wasted. Not only that, as we rub our hands together small amount of skin are worn away, this might not be a problem for us as our bodies have a capacity for self-repair but with machines this isn’t the case and wear and tear will damage the machine.

All I found. lol