Battling Top Design:http://www.youtube.com/watch?v=-Uw5crBtIqs

http://www.youtube.com/watch?v=AvEwpLV8-R4&NR=1

What makes a good Intro Projectcompetitive outcome wide design space low tinkering coefficient low math abilityuse of SolidWorks/Matlab/Excellow material costlow fabrication skilllink to science related topicssafety

Coil Gun Rankingcompetitive outcome 2wide design space 2low tinkering coefficient 2low math ability 10use of SolidWorks/Matlab/Excel 5low material cost 2low fabrication skill 9link to science related topics 9safety 5SCORE 46

"Battling Top" Rankingcompetitive outcome 7wide design space 7low tinkering coefficient 7low math ability 10use of SolidWorks/Matlab/Excel 8low material cost 8low fabrication skill 9link to science related topics 9safety 10

SCORE 74

Catapult Rankingcompetitive outcome 9wide design space 7low tinkering coefficient 7low math ability 10use of SolidWorks/Matlab/Excel 6low material cost 6low fabrication skill 7link to science related topics 9safety 5

SCORE 66

Rules

• Core Material limit – 2"x2"x2" aluminum cube– plus anything you want to screw/fasten into it • like a shaft for launching

• Design own launcher (acrylic possible)• Rip cord < 24"• Arena will be some bowl shaped thing– anyone have a snow disk?

• http://www.youtube.com/watch?v=uerlueDxUqM&feature=related

Tops involve angular rotation, a challenging engineering topic

• Moment of inertia• From Wikipedia, the free encyclopedia• In classical mechanics, moment of inertia, also called mass

moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, (SI units kg·m²) is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation. The moment of inertia plays much the same role in rotational dynamics as mass does in linear dynamics, describing the relationship between angular momentum and angular velocity, torque and angular acceleration, and several other quantities. The symbol I and sometimes J are usually used to refer to the moment of inertia or polar moment of inertia.

Moment of Inertia• Overview• The moment of inertia of an object about a given axis describes how

difficult it is to change its angular motion about that axis. Therefore, it encompasses not just how much mass the object has overall, but how far each bit of mass is from the axis. The farther out the object's mass is, the more rotational inertia the object has, and the more force is required to change its rotation rate. For example, consider two hoops, A and B, made of the same material and of equal mass. Hoop A is larger in diameter but thinner than B. It requires more effort to accelerate hoop A (change its angular velocity) because its mass is distributed farther from its axis of rotation: mass that is farther out from that axis must, for a given angular velocity, move more quickly than mass closer in. So in this case, hoop A has a larger moment of inertia than hoop B.

• The moment of inertia of an object can change if its shape changes. Figure skaters who begin a spin with arms outstretched provide a striking example. By pulling in their arms, they reduce their moment of inertia, causing them to spin faster (by the conservation of angular momentum).

• Scalar moment of inertia• Consider a rigid body rotating with angular velocity ω around a certain axis.

The body consists of N point masses mi whose distances to the rotation axis are denoted ri. Each point mass will have the speed vi = ωri, so that the total kinetic energy T of the body can be calculated as

• In this expression the quantity in parentheses is called the moment of inertia of the body (with respect to the specified axis of rotation). It is a purely geometric characteristic of the object, as it depends only on its shape and the position of the rotation axis. The moment of inertia is usually denoted with the capital letter I:

• It is worth emphasizing that ri here is the distance from a point towards the axis of rotation, not towards the origin. As such, the moment of inertia will be different when considering rotations about different axes.

• Similarly, the moment of inertia of a continuous solid body rotating about a known axis can be calculated by replacing the summation with the integral:

• where r is the radius vector of a point within the body, ρ(r) is the mass density at point r, and d(r) is the distance from point r to the axis of rotation. The integration goes over the volume V of the body.

Ycm, height of center of mass

• Ycm is the average height of mass distribution making up the top. if you wanted to balance it from a string, sideways, Ycm is where you would attach the string:

Ycm

Stability Coefficient

• The overall stability of the top, based on some approximations, is indicated by:

• stability = Rg/Ycm – Radius of Gyration divided by – the height of the center of mass

• Implications:– increase Rg, stability ++– decrease Ycm, stability ++

The calculations are daunting

• If we wanted to try a number of different designs, it would take forever

• Fortunately engineers use computer tools such as Matlab to speed the development of design