Fuzz in a tennis ball

Today during practice, I became aware as to why a tennis ball is fuzzy.  The fuzz is a product of the felt on the outside of the ball.  This is done to produce drag on the ball to slow it down.  With the newest technology in tennis rackets, professional tennis players are hitting the ball at great speeds.  The fastest recorded serve is 251km/hour!  The felt acts as a dampener when the ball bounces so that the ball doesn't bounce too high or too quick.  Without the felt, the game would probably be too fast for professional tennis players.  When a ball looses the fuzz on it, it becomes more bald, and starts to bounce quicker and higher, making it more difficult to control.

Ski Jump

I saw a picture of a skier (snow skier) today and saw that when he was airborne, he leans forward and pins his arms to his sides.  This is done to reduce air resistance.  The leaning forward creates a positive angle of attack against the wind, and being in a straight line with arms and ski poles pinned to the body minimizes air resistance and air drag

Dimples in the golf ball

Today, I became mindful of why a golf ball is is shaped the way it is (specifically, why it has the dimples on it).  When the club strikes the ball, the ball takes off with backspin on it.  The ball pushes down on the air, so air must push up on the ball for it to continue moving. The dimples help to carry the air along with the ball and make the air follow the curvature of the ball. Without its dimples, the ball would not travel as far as it does.

Flow in cigarette smoke

I saw a cigarette on an ash tray today and noticed how the smoke moved.  Close to the cigarette itself, the smoke moved in laminar flow.  As the hot gas continued to move up in the air, it turns into turbulent flow. It turns into turbulent flow as its Reynolds number and its velocity increases.

Blowing air in bottles

Today, I blew on the top of a glass bottle and realized that I could make sounds by doing this.  This is because when I blew, I created a jet of air that was moving into the bottle. Pressure builds up in the bottle, until the pressure pushes the jet of air back out.  The air that is moving out decreases the pressure in the bottle. This creates a vibration, creating the sound.

Pressure: Force per Unit Area

Today, I found a tack in my room.  As I was pushing against my cork board, I became aware that the pressure is greater at the tip of the tack, than at the blunt end.  One would think that it is just because of the pointy end, but it's a little more than that.  The area in the blunt end is greater than at the pointy end. This makes pressure decrease in the blunt end. The equation for pressure is force per area.  This means that even if the same force is applied, if the area is greater, the pressure created will be decrease.  This is why putting force at the blunt end of a tack hurts less and creates less pressure on the finger.

Floating helium balloons

While thinking about helium, I became mindful of why helium balloons float, while air balloons that we blow up ourselves don't.  The main factor is that helium is less dense than air (air contains nitrogen and oxygen).  Helium is also lighter than air.  Just like heavier things tend to sink, and lighter objects float, the lighter helium balloon will float and rise when it is in air.