3.1 What is Energy?

Friction

You've learned a bit about friction before.  

Let's review a few things:

  • friction always opposes motion
  • any two surfaces rubbing will cause friction
  • the rougher the surface, the greater the friction
  • friction creates heat
  • kinetic friction means friction while moving (hint: "kinetic" means moving)
  • static friction means friction while not moving (hint: "static" means stationary)

So, let's relate this to energy:

  • friction causes energy conversion
  • the energy created by friction is heat (thermal) energy

Most often, friction get's a "bad rap." 

  • it would be so much easier to swim fast without all the friction of water
  • I wish my shoes wouldn't give me blisters
  • cycling could be so much faster without the air resistance
  • it would be so nice to have more efficient cars
  • NASA has spent billions trying to figure out how to handle the heat of friction upon reentry into the atmosphere by the space shuttle
  • playing soccer in long grass is painful as the passes never get far enough
  • I need to wax my skis because they're getting too slow (snow friction)

Sometimes, though, we realize that life without friction would not be good.

  • I'd like more friction so my brakes worked better
  • the lack of friction on icy days makes driving unsafe
  • I wish I had more friction when trying to open a jar
  • when I crash when biking, the road sure makes nasty scars
  • running on ice certainly makes you appreciate friction
  • good tires sure make your car or bike handle nicer
  • when I'm cold, it helps to rub my hands together

Energy Lost due to Wind Resistance
Wind resistance is another form of friction. The faster you go, the greater the wind resistance and the more energy you need to overcome. When traveling at 80 kilometres per hour, the average car uses around half of their fuel energy just to overcome the wind resistance.