Kevin Irwin
Physics SL: Period 7
May 5th, 2017
Measuring the Backspin of a Baseball and the Maximum Height Reached
Exploration:
Introduction:
Projectile motion is a form of motion in which an object is thrown near the earth’s surface, and moves alone a curved path under the action of gravity only. It is implied that all other external forces, such as air resistance and drag, are neglected, and gravity is the only force acted upon the object, in a downward motion. Due to Newton’s first law of Inertia – “Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it” (Philosophiæ Naturalis Principia Mathematica) – there is no horizontal force needed to maintain
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The ball pushed the air down, which in turn, the air pushes the ball up – according to Newton’s Third Law “For every action, there’s an equal and opposite re-action” (Philosophiæ Naturalis Principia Mathematica). Because the air pressure of the ball is high on the bottom of the ball, the pressure will automatically try to rotate to the top of the ball, which will lift the ball in trajectory.
Figure 2
This change is pressure is known as Bernoulli’s Principle. Generally speaking, faster moving fluids – or in this case air – will cause the bottom of the ball to have greater pressure than the top, producing a greater lift (Hydrodynamics & Hydraulics).
However, in baseball, unless the ball is launched at an angle, the backspin generally exerted on the ball is not enough to create a significant difference in the flight path of the ball, and the ball will travel straight until the velocity is not fast enough and gravity acts upon the ball, pulling it towards the ground. But the backspin helps increase the flight time of the baseball and allows some people to throw 150 kmh-1.
Figure