Science Buddies: "Ask an Expert"

I am doing my science project on if changing the weight of baseball by freezing or by soaking in water will affect how far the ball can be THROWN. I need to control the force and speed of the throw to make a good argument. Will I have to use a pitching machine or is there another way? I thought about a sling but don't know how to measure force and speed.

Hello and welcome to the science buddies forums! You are absolutely correct that you will need to control the force and speed of the ball. You could use a pitching machine, if you have access to one. However, you could build a small catapult to achieve the same thing. I just helped my son make one for school, and it was pretty easy, requiring standard tools and skills. After a break-in period, the catapult should supply (approximately) the same force each time you launch it. You must bring the lever back the same amount each time, but you can do this by marking your catapult.

One thing to consider is that since F = MA, if you supply the same force each time, the acceleration will be linearly dependent on the mass (weight) of the ball. Since you want to know "if changing the weight of baseball ... will affect how far the ball can be THROWN", you need to define what you mean by "how far can be THROWN"? That almost sounds like you are looking for the absolute fastest terminal velocity possible for each ball. That is not the same thing as "control(ing) the force and speed of the throw." Could you please reply with a more specific idea of what you want to measure? Then we can help you figure out more about controlling the experiment. Thanks!

In terms of knowing what the actual launch velocity of the ball is, you can calculate that by measuring the height and distance the ball travels on each launch.

Keith

I plan to use the same acceleration and angle each time the ball is thrown (will probably use a pitching machine). I want to research what happens when the weight of the ball is changed by freezing or by soaking in water. I am testing my theory that the heavier ball will go further.

Hi and welcome back to the forum. Just a few bits of information so that you can do your best with this experiment.

You probably know that Newton's 2nd law is F = ma, where m is mass and a acceleration. If the pitching machine is applying the same force each time, then the lighter ball will get the most acceleration and go the farthest. If somehow you have a machine that can change the force so that each ball gets the same acceleration, assuming that each ball presents the same size to the air resistance, you should get the same distance (how you do this is beyond me .

Please also note that you say you are testing whether the heavier ball will go farther, but the variable you mention is freezing and soaking in water.

Let us know if you have any questions!
Keith

Hi terry57,
In addition to the good advice from Keith, I recommend reading up on air resistance, or "drag". Your idea that the heavier ball will go farther might be based in part on past observations that heavy objects that we tend to throw (balls, rocks, etc) do tend to travel farther then similarly sized, light objects (crumpled paper, balloons, etc). This results partly from the force of air resistance, which increases proportionally to the square of velocity. Whether this will be a major factor in your experiment will depend on details of your experimental design.

Here are a couple of web pages with information on air resistance. You can find many more by running an internet search for "air resistance".

http://www.glenbrook.k12.il.us/gbssci/p ... /efar.html
http://en.wikipedia.org/wiki/Air_resistance

Good luck!
Chris