Give two reasons why it is useful for the cyclist to reduce friction as much as possible
Answers
Answer:
The answer has to do with energy. In the case of the cyclist, she wants to turn as much of her chemical energy (food) into mechanical energy (motion). For the sake of simplicity and to focus on the question of friction, let us keep our discussion limited to cycling along a long, flat, straight road.
The mechanical energy of motion is called “kinetic energy” and can be calculated by multiplying one-half the mass of an object times the square of its speed. Ignoring friction, if you want to go faster with the same amount of energy, you only have one choice: ride a lighter bike.
So where does friction come in? Well, if you are riding your bike on a windless day, you will still feel the “wind” in your face as you ride because your body is pushing air out of your way as you move through it. Although air is light, it still has mass, and if you are taking motionless air and turning it into moving air (by pushing it out of your way), you are giving the air kinetic energy. That kinetic energy had to come from somewhere, and in this case it came from you by slowing you down.
You are pushing the air out of your way, and because of Newton’s Third Law (for every force, there is an equal and opposite force) the air is pushing back on you. We call that resisting force “air resistance”, or the “friction” of the air against our motion.
Although our cyclist is trying to turn all of her chemical energy into her kinetic energy, some of her energy is being bled off into the surrounding air instead, because of friction. By reducing friction, more of her energy can be used to make her go faster.
Here is some additional information which may be useful to you. “Work” is just another name for the transfer of energy. The work done against air resistance is equivalent to the force of the air resistance times the distance over which that force is applied.
The force of the air resistance depends on your speed relative to the air (along with many other usually-smaller factors like the air temperature, pressure, and humidity), but in fairly complicated ways. Basically, the faster you go, the greater the air resistance and the faster that air resistance increases.
