football, throwing a football

[clubgch]

how dowes the weight of a football affect the distance being thrown.

[Precursor562]

The lighter it is the less effort it takes to move it by using your arm. The greater the mass something has the more inertia it has. Inertia is an objects resistance to accelerate. Mass on earth has a direct relation to weight (mass in kg times 2.2 equals weight in pounds approximately) due to gravity. Gravity accelerates mass creating a force in Newtons. Pounds is the same thing using a difference unit of measurement.

Newton is an SI unit (International Unit of measurement for measuring force)
Pound is an English unit (also used to measure force)

So the lighter something is weight wise the less mass and therefore less inertia it will have. This allows you to accelerate your arm to a faster velocity while holding something light compared to something heavy. Which allows you go give something light more velocity upon release than something heavy.

However that only answers one part of your question. The velocity imparted to the object.

The more mass something has the more momentum it will carry. In other words the more mass something has the more force (in this case drag) is required to slow it down. Which is why a football is shaped the way it is but I'll get to that in a bit. Now although you can throw the lighter object at a faster velocity it takes less force (drag) to slow it down. So if you were to accelerate two objects to the same speed and both object were spheres of the same size (therefore having equal drag) but one was heavier (having more mass per volume (density)) than the other the heavier sphere will travel farther since the lighter sphere will slow down faster.

Now for size and shape. If you had two spheres of lead. One is 1 cubic inch and the other is 8 cubic inches. The 1 cubic inch lead ball will be able to be thrown at a faster velocity than the 8 cubic inch ball due to it being lighter. Now although the 1 cubic inch ball is lighter and should slow down faster than the 8 cubic inch ball it is also 1 eighth the size so it has less drag. Ultimately the 1 cubic inch ball of lead will go farther than the 8 cubic inch ball of lead. Which finally brings me to the shape of a football.

If a football were completely round it would have more drag than it does now when thrown properly. When thrown it is thrown pointy end first so that it 'cuts' through the air with less resistance. This has to do with the angle at which the drag forces apply. When the drag forces are applied at a 90 deg angle to the surface of an object the force is at its peak. The farther you deviate from this 90 deg angle the less force is felt by the object. So to make sure the ball doesn't tumble and stays pointy end first throughout its flight it is give a certain amount of spin. For a perfect balance (ensuring the ball doesn't develop any Yaw (wobble)) there is a ratio that needs to be met. This ratio is the spin in comparison to the velocity of the ball. The faster the ball is thrown the faster it moves through the air and so the faster it must spin to maintain the proper level of gyro stabilization. Of course the rate of spin also depends on the dimensions of the ball (size and shape) but since we are talking about footballs (rugby balls excluded) then they are all the same size.

This post has been edited by Precursor562 on Feb 26 2007, 12:53 AM