What is a good gel or gels that I can use for Sci Fair!!!!!!

[burtonboi]

My sci fair question is: Will a more viscous gel be more effective at resisting the kinetic energy of a projectile?

Hypothesis. A gel with a higher viscosity will be more effective at dampening the kinetic energy from the impact of a projectile.

I will be dropping ball bearings onto the gel and measuring its effects.

What is a good gel/gels of different viscountcies that I can use?
How about jello and I can change the viscosity by adding differing amounts of water?

[MelissaB]

Hi,

I have moved your thread to the physical sciences forum because I think you will get more help here. Good luck!

[rmarz]

Burtonboi - I don't think adding more water to Jello will give you a controlled viscosity medium. I think that Jello either 'sets' or doesn't set. You might want to read up on simple viscosity measurement devices such as a Zahn cup, a simple device to measure paint viscosity for paint applications or the link to the Ford cup (link below). You could use a viscous medium such as corn syrup to experiment with. Create a cup measurement standard and measure several points starting with pure corn syrup, then dropping your projectiles and measuring time/distance. After measuring the most viscous setup, slowly add water to thin the medium, one step at a time, measure the viscosity again, and measure your projectile data. Repeat over and over adding a little water to each step. You should be able to get about a half dozen readings to correlate before the liquid thins too much to time the projectile drop accurately.

http://en.wikipedia.org/wiki/Ford_viscosity_cup

Rick Marz

[burtonboi]

Thanks rmarz. Yes your theory on the jello makes sense. Where would I be able to get a Zahn cup? I also heard I could use a Durometer to measure the viscosity? Lastly, would corn syrup be classified as a gel, since my project is centered around gels.

[rmarz]

burtonboi - Sorry, I missed your hypothesis a bit. You did say gel, not viscous liquid. A gel is defined as a colloidal suspension and has very different qualities than a liquid. I don't know if gelatin (Jello) will thin properly with water. Perhaps some common products like hair gels can be thinned enough to give you measurable results. With regards a Zahn cup, you could fashion your own using a small container like a 35 mm film container and drill a small hole in the bottom. Fill the container to the same level and measure the time to empty for each of the various viscosity materials. You mentioned a durometer, but my memory is that it is an instrument to measure the hardness of rubber and plastics, nothing that would flow like a thin gel. It would probably work on a really hard gel, like ballistic gelatin, but your experiment seems more appropriate to the viscous liquid or gel.

Rick Marz

[burtonboi]

Question. Will a more viscous gel be more effective at resisting the kinetic energy of a projectile?
Hypothesis. A gel with a higher viscosity will be more effective at dampening the kinetic energy from the impact of a projectile.
Materials: Various gels of differing viscosities, equal number of panes of glass as gel, ball bearing( dimensions to be determined) Material to mark gel, container to hold gel in place over glass pane.
Procedure.
• Take multiple samples of gels, each of varying viscosities. Number of samples is yet to be determined.
• Projectiles, most likely metal ball bearing, all going to be off equal dimensions such as diameter, radius, weight, etc will be used to make impacts on gel.
• Each individual sample of gel (all with equal depth and width) will be place on a sheet of thin glass. The weight of the gel affecting the strength of the glass will be taken into account.
• Markers to measure the area of impact horizontally and diagonally across gel will be put into place.
• Damage done by projectile to gel and if any, the pane of glass, will be measured and recorded.
The projectile (ball bearing) exerts force on the gel. This force is defined by the equation: a = F/m, or F = ma.
"Isaac Newton's Second Law, which forms the foundation for classical mechanics. Newton's Second Law states that the acceleration (a) of an object is directly proportional to the force (F) applied, and inversely proportional to the object's mass (m). " (Nice, What is Force?)
So (a) stands for the force being applied on an object, in this case gravity (since gravity is pulling the projectile downwards) which is equally proportional to the acceleration of the object. (F) stands for the force being exerted on the object. The force as previously mentioned is gravity. (m) is the mass of the object in which it has a negative correlation with (F). This means that the force being applied to the object is inverse that of the object's mass. In summation, this means that greater force means a higher rate of acceleration of an object. But influencing that, is the mass of the object. The greater amount of mass an object posses, the slower the object will accelerate, as stated in Newton's Second Law.
The energy created by the projectile as it falls to the gel is called kinetic energy. Kinetic energy is the energy of motion. (Nice, Kinetic Energy) The formula to determine the kinetic energy of an object is KE = 1/2*m*v2. Breaking down the equation: KE which stands for kinetic energy is equal to 1/2 times the mass time the velocity squared. Mass is the measure of the amount of matter in an object and velocity is the rate of change of position.

3
Glass will break when a "force moves toward the glass and pushes it inward, the glass eventually cracks and breaks." (Watts) Regular glass is composed of mixture of silica, soda, and lime. (Smith)

[rmarz]

burtonboi - Thanks for the more detailed description of your experiment. I better understand the nature of your questions. In many ways it looks similar to the popular science experiment of trying to insulate an egg for a controlled drop without breaking. It's all about controlling the peak forces on your target.

You are looking at the viscous gel to absorb energy before it can be transmitted to the glass and possibly break it. There are a few new variables that creep into this setup. The gel is distributing the energy in many directions at once. You are using the formulas for kinetic energy to translate into the force values that the projectile is delivering to the glass. Obviously if the gel is slowing the projectile's velocity and distributing energy in many directions, it is reducing the instantaneous force that is transmitted to the glass. That seems to be part of your hypothesis. There is also a dynamic issue, and that is at what rate does the gel displace (to absorb the energy). At the instant of contact, the energy (and force) is maximum, and it would decrease as the gel absorbs more of the kinetic energy (as the projectile moves through it). Here is where you may have an interesting 'hypothesis meets reality' moment. It would seem that a more viscous gel would slow the projectile down faster than a less viscous gel. However, it would transmit more energy faster and could cause the glass to break at minimum energy (as an extreme, say your gel was similar to a very high durometer material like a sheet of hard rubber). In contrast, a very thick, but low viscosity gel (as an extreme, say water like,) the projectile might have time to expend most of it's kinetic energy at a rate that never exposes the glass to a force that would fracture it. You have a question that the designers of armor have, whether it is designing protective pads in motorcycle apparel or bullet-proof vests. How much distance and area do I have to get rid of or distribute the energy to safe force levels (per unit of area).

This extreme would be like a police ballistics lab where a bullet is discharged into several feet of water and virtually unblemished as most energy is bled off in the water. I hope I haven't confused you with too many conflicts. Maybe this might help in formulating your hypothesis and reducing some variables in your testing.

Rick Marz

[burtonboi]

Thank you Rick. That was extremely helpful. I was thinking about using samples of both jello, gelatin, and ballistics recipes.
Would this be an acceptable recipe?: http://www.myscienceproject.org/gelatin.html

Also what could I use to measure the viscountcies between the different gels?

[rmarz]

burtonboi - The recipe you provided looks like it would provide a very firm gelatin, similar to ballistic gelatin. I think you are going to need a much softer material if your intent is to simply drop a ball bearing from any reasonable height. It might simply 'bounce' off this recipe. Ballistic gel formulas are meant to be penetrated by projectiles with significant velocities of hundreds up to a few thousand feet per second. Dropping your sphere will not achieve that. That was one of my thoughts about using a viscous liquid as an alternate material.

To measure the degree of hardness of a ballistic type gel, the instrument would be a durometer. It basically measures the depth a probe will penetrate the material being tested with a specific pressure after a period of time. You could make your own simple durometer using a weighted nail (blunt the point). Here is a link to a Wikipedia reference on how they work and the procedure for using the durometer.

http://en.wikipedia.org/wiki/Shore_durometer

Rick Marz

[burtonboi]

So a ballistics gel would be too hard. So I should just make regular gelatin? And to get varying viscountcies I would vary the amount of water in the mix?

[burtonboi]

Also for the durometer, I simply use a blunted nail and just let it be dead weight on the gel? And if it penetrates 2.5 mm into the gel it gets a reading of zero and if it does not penetrate it gets a rating of 100?

[SRGT BUBBLES]

hello,

i believe Burtonboi is a good choice!

All the best!

[burtonboi]

Thank you srgt bubbles. Could you please suggest a viscous liquid Rick? Maybe a syrup for example? The reason I have to stick with gel's are because I already submitted the papers to the science fair panel.