I am so confused BUT my son isn't- please help

[jammeff]

One of my sons has choosen:
Question: How will the weight of a football affect the distance it travels?

Hypothesis: Based on what I have researched, I believe that if the weight of the ball is heavier, then it will travel further because the force of physics in conjunction with gravity on the ball will be greater giving it a higher rate of speed as it comes down.

I know NOTHING about this topic. He did his research, then the experiment. It sounds plausable (that's coming from someone that is not good at science). His experiment outcome was the heaviest ball 4 out of 5 times went the farthest. When he told his dad, his dad said there was no way. The lighter the ball the farther it will go. This is the complete opposite of what my son is saying. I've researched this for 2 hours and have not found anything. Both think they are right- which one REALLY is.

These experiments are so hard.... my younger son is just finishing up his mold/bleach experiment. My head is spinning from this two projects.

THANK YOU for any help you can give or direction.

[jammeff]

here is a little more info:

Variable: 3 footballs with different weights.

Independent Variable: the football

Control: all three footballs are the same size.

[barretttomlinson]

My instincts are to trust your son. He did the experiment, and assuming he is accurately performing the experiment and honestly reporting his results(and I suspect he is), his results are his results. If your husband disagrees, then the burden of proof is on him to repeat the experiment himself and test his position.

If two footballs are exactly the same shape and thrown at the same speed and angle, but one is heavier than the other, the heavier one will have more kinetic energy and momentum. The drag on the balls from air resistance should be the same, causing the lighter ball to lose kinetic energy proportionately faster than the heavier one.

In science, experiments always trump theory. Congratulations to your son for standing up for himself, and believing his own eyes.

[Terik Daly]

I echo barretttomlinson opinion. What the experiments show, the experiments show.

And let me share how much it means to hear from a parent who is so clearly dedicated to their children's education. I applaud your effort! Parental support is critical to a child's success. Even though you may feel that your head is spinning, know that your support has made a difference in your children's lives. Thank you for being a supportive parent.

[jammeff]

Thank you to both of you for your words of encouragment and help.

Well I bought different balls and he did the experiment again today and the lighter ball went further .

I know this is going to sound HORRIBLE for we (my son and I) are OVER this project. Its due tomorrow and at 10:16 he does not have the research notebook, board, or paper anywhere near being done.
I know what your thinking why are you doing this last minute. I have a good reason he just got done with a history fair project last Tuesday (which he won in his division- Sport History- he can't get enough of sports).
He did start this project actually awhile ago. His Science teacher approved him to do "How the size of the ball affects how far it will travel"- his teacher said the balls all had to be the same weight which we couldn't find. So DH and son attached weights to the balls and did the experiment that turned out to be a mess (DH AGAIN said no matter how much air is added to the ball the weight will remain the same, which I found to be false today when I was adding air to the new balls). Hence two days ago we changed the problem and hypothesis and he did his experiment. Last night we made the mistake of sharing his results w/ his dad and again as stated above he messed us up. My son held strong and got I mixed up not really understanding the whole thing. Which brings us to where we are right now. He has decided to stay with his experiment he did 2 days ago and scratch the 2nd attempt he did today and is going from there...... so we'll see.

I did let my son read what you both wrote and it made him feel so much better.... thanks again

[jammeff]

OK below to what he change in bold print. Also can the control be several things and the variable be only one thing that changes?

Question: How will the weight of a football affect the distance it travels?

Hypothesis: Based on what I have researched, I believe that if the weight of the ball is heavier, then it will travel further because the force of gravity in conjunction with the motion of physics on the ball will be greater, giving it a higher rate of speed as it comes down.

Variable: 3 footballs with different weights.

Independent Variable: the football.

Control: all three footballs are the same size and shape.

[John Furman]

Hey Folks,
I have been interested in your postings and have resisted commenting until now. It seemed to me that the weight of a football does not affect the distance it travels. I have reviewed the equations of motion for the football and found that the weight effects (mass) drop out of the problem leaving the traditional second order equations to be solved. This may be why the experimental results may not be conclusive on the weight effects. I recall the Myth Busters testing this question by punting the football and finding the same conclusion.

[ChrisG]

Hi John,
Interesting point. For this particular experiment, I agree with you that the experimental error could easily be larger than the actual differences in travel distance due to mass. In regards to the theory, I agree with Barrett that a lighter football will lose a greater proportion of its momentum to air friction (were you using equations for frictionless motion?). Consider punting a very light football that is essentially a balloon - it would hardly travel at all. Depending on how the football is being launched, there could be other effects of mass. For example, imagine trying to punt a lead football and a regular football, versus shooting them out of a cannon.
My 2 cents,
Chris

[davidkallman]

Hi jammeff,

One website to check is: http://www.swarthmore.edu/SocSci/Educat ... throw.html

It's looking at the same type of project you are looking at. It may not be directly applicable, but it can give ideas for posters etc.

[peteryoung]

Jammeff:

The football experiment you describe falls into a aerodynamics subset where the motion is primarily one-dimensional (along its trajectory) and where aerodynamic drag predominates. In these situations, acceleration and deceleration of the object is dominated by the "ballistic coefficient",
a parameter which is weight divided by (drag coefficient times frontal area). Objects with low ballistic coefficients will accelerate more slowly, and decelerate quicker, than objects with higher ballistic coefficients (given the same initial conditions).

Example of low ballistic coefficient: badminton shuttlecock or whiffleball
Example of high ballistic coefficient: a golf ball.

In the experiment you describe, it would be ideal to have the same energy applied to the different-weighted footballs. Throwing these
"by hand" is bound to introduce variations due to the different weights,
and this complicates the analysis. Accounting for this impt. effect would be a good topic to discuss as you plan your experiment and analyze the data. Can you devise a method to minimize this effect --

For more information on ballistic coefficients, Wikipedia has some
relevant information. I hope this helps.

Peter Young

[Terik Daly]

Jammeff,

To answer your other question:

Also can the control be several things and the variable be only one thing that changes?

A control is anything that you keep the same between experimental groups. So it is very likely that you will have multiple controls. The independent variable should be the only thing that you change, in your case, the independent variable is the weight of the football. Size and shape, as you have mentioned, are both controls.

Glad to hear that things are going well. Keep up the good work!

[zzzzdoc]

One thing I've learned over the years is not to argue with rocket scientists.

Here's a synopsis from the Mythbusters Web Site.

Helium Football/Catching a Bullet
Written by Doolley012
Monday, 20 March 2006
Helium Football
Air Date: February 1, 2006
Episode #47
Helium Football/Catching a Bullet

The Myth: A football filled with helium will fly farther than one equally pressurized with air.

The Possible Source: A kicker who played for the Oakland Raiders from 1973 to 1986, Ray Guy, had an astonishing kick, which made the ball seem to stay in the air for exceptionally long amounts of time. This period in the air was dubbed hang time. Reportedly, during a game in the 70's, one had such a spectacular hang time that the ball was immediately collected and tested for the presence of helium. It came up negative.

The Experts:
Debrah Nolan [Statistician] provides Adam and Jamie with expert analysis of the data collected during their experiments.

Memorable/Quotable Moments:
"I put everything on my head." - Adam
"Well, yeah, but we would, you know, aspire to not be idiots." - Jamie

The Action/Results: To begin, Adam and Jamie travel to San Francisco City College where they meet with football coach John Balano and kicker Tim Sonnenburg. After getting some pointers on proper kicking techniques (and humorously attempting) the two agree that the college kicker would be the best choice for sending the ball downfield. Ten trials are performed, five with helium and five with air. The data collected shows the balls filled with helium went an average of 3 yards farther than the ones filled with air. Unfortunately, there were too many outliers in the data set, and so Adam and Jamie, unsatisfied with the method, contemplate how to achieve more accurate results.

The next experiment is simply to determine how large a difference of weight is given between the two footballs. After emptying the ball and refilling it with the standard 13psi of air, they find the ball has gained 3.2 grams in weight. The ball is once again flattened, filled with helium and weighed. Surprisingly, it is almost 7 grams lighter than the ball filled with air - even lighter than the football without anything in it. Following this, the two pressurize a football using Grant's bottle rocket rig until a satisfying explosion occurs.

To eliminate human and atmospheric variables, Adam and Jamie set up a kicking machine in an indoor hangar at Moffet Field. Jamie sets up a bungee cord to trigger the firing mechanism to further avoid human error. Jamie then proceeds to fire twenty air filled balls through the hangar, followed by twenty helium balls while Adam marks and records their distance. In the end, the Mythbusters have 60 data points and take the records to statistician Debrah Nolan. She finds that the air filled balls actually had a one-inch advantage, but declares the data inconclusive.

The two finally decide to test the transfer of energy from a kick to the ball. By modifying the A-frame shock rig used in the catching a bullet myth, Adam and Jamie can give a determined amount of force to the ball from a pendulum-like motion. After "kicking" the balls with a hammer and viewing the resultant high-speed film, they find
that both the air-filled and helium-filled balls had the same speed. The helium balls did not have the advantage.

The final conclusion was that because the helium balls were lighter, they were more susceptible to drag when flying through the air. The very thing that should've made them fly farther, was, in fact, causing the balls to move a slightly shorter distance.

Myth Busted!

[bradleyshanrock-solberg]

The reason you get two "intuitive" answers is that there are two factors at work here.

1. Force to move the ball. The father would be correct if you were throwing the ball in a vacuum - it takes more force to throw a heavier object. If it was thrown equally hard, the lighter one would always go farther.

2. Air resistance, and aerodynamics. Try to throw a piece of paper sometime. Wad it up and throw it. Dip it in water, wad it up and throw it. The first two weight the same, but the wadded up ball will go farther - it has better aerodynamics...less air resistance per weight. The soaked piece of paper will do even better in spite of the fact that it weighs more, possibly a lot more. The ability of air to slow it down compared to its weight is better than that of the dry wad of paper. Now make a paper airplane, the kind designed for distance. It'll do far better than even the wet wad of paper, because it is designed to use the air to generate "lift" and go even further. The math for this is nasty - I got it in my third year of mechanical engineer training in college. You can't predict this stuff with a high school math...only by observation. (even with the math, it's still something of an art. People who make better wings for airplanes make a lot of money)

Footballs are designed to be thrown a long distance in Earth's atmosphere. Further they're designed to throw controllably when there is a bit of spin on the throw...the shape is very important to the game and how they behave. They have some of the properties of a paper airplane, in that when thrown properly, air can actually assist how far they fly, it's not all "resistance".

Without doing research I could not predict whether your son's hypothesis would be correct, because it is hard to know whether a heavier ball would ruin the aerodynamics of the ball (or make it just too heavy to move from a force standpoint overcoming any aerodynamical advantage).

With a baseball...changing it to a softball does ruin it. You can throw a baseball much faster and further than you can throw a softball, and also make it do "tricks" (curve balls etc). Take off the stitching and it also changes....it's a funny creature.

So I think your son did something really interesting, and you should trust his results over his father's intuitive opinion....however my real recommendation is to have your father try to duplicate the son's test. This is called "peer review" in science - if he gets a different result, you need to see how they each perform it, and what they're doing differently.

(perhaps being more or less skilled at throwing a football could skew the results, for example)