Reading Flashcards
drag occurs when molecules of ..
a fluid collide with an object and take energy away from it
what is important about the leading shape of an object in fluid
if the leading edge if pointed, direction of fluid will be changed more slowly
- helps to maintain laminar flow
what is important about the tail end shape of an object in fluid (AND WHY)
minimise the turbulent flow by tapering the tail of an object
this is because as an object moves through a fluid, a region of low pressure is left behind it
air always moves from high to low pressure, so the air will rush here, creating more turbulence
explain why golf balls have dimples
as the ball passes through the air it creates turbulent flow behind it due to pressure differential
at some critical speeds : there is a formation of turbulent boundary layer which allows for more laminar flow
the roughness of balls increased the rate which turbulent boundary layer is formed, reduced ball speed needed to reach the critical level where drag is decreased
the dimples in a golf ball will increase what
increase the boundary layer in front and decreases it at the back, creates turbulent boundary layer of air around the ball
what happens to air separation due to dimples in golf ball
in a smooth ball the air separates quickly from the ball but in a golf ball the turbulence sucks air to the ball and separation is delayed,
this results in less drag
how to reduce wave drag with arms in swimming
lead arm should stretch in front as propulsion pushes backwards
bernoullis theory is based on the idea that the energy if a fluid is not changing, its total energy is proportional to
its kinetic energy, potential energy and pressure
explain why a spinning ball will swerve
spinning ball grabs air because of friction btwn air and the ball
boundary layer spins with the ball
collisions with oncoming air + ball or air spinning causes air on one side to slow down
differentials in speeds creates pressure differential
what is the magnus effect
the spin you put on a ball will eventually cause pressure differential and the ball will start to swerve
what is the magnus force
the force created by unequal pressures
the faster the ball spinning the greater the
magnus force
explain the conventional swing
seam and shinny side faces batsman
laminar flow is created around the shinny side
turbulent flow is created on the other side as the seam disrupts the flow of air
creates pressure differential
lower pressure on the turbulent side
greater pressure on the laminar side
this causes the ball to swing in the direction of where the air pressure is low : it moves with the seam
explain the reverse swing
balls rough side and seam face the batsman
turbulent flow over the rough side
turbulent flow created on the smooth side due to the seam disrupting the flow of air
but turbulence on the rough side is more than that of the smooth side
air pressure is greater on the rough side than the smooth side
this makes the ball swing in the opposite direction of the seam : reverse swing
how to find resultant force
square of horizontal + square of vertical = square root of both of these
