Improve math skills of your kids - Learn step-by-step arithmetic from Math games

Math: Unknown - Step-by-step math calculation game for iOS.


Math: Unknown is much more than a math game. It is a step-by-step math calculation game which will teach users how to calculate in the correct order rather than just asking only the final calculated results.

The app consists of four basic arithmetic operations which are addition, subtraction, multiplication and division. In order to get started, users who are new to arithmetic can learn from animated calculation guides showing step-by-step procedures of solving each type of operation. It is also helpful for experienced users as a quick reference.

Generally, addition and subtraction may be difficult for users who just start learning math especially when questions require carrying or borrowing (also called regrouping). The app helps users to visualize the process of carrying and borrowing in the way it will be done on paper. Once users understand how these operations work, they are ready to learn multiplication and division.

For most students, division is considered as the most difficult arithmetic operation to solve. It is a common area of struggle since it requires prior knowledge of both multiplication and subtraction. To help users understand division, the app uses long division to teach all calculation procedures. Relevant multiplication table will be shown beside the question. Users will have to pick a number from the table which go into the dividend. Multiplication of selected number and divisor is automatically calculated, but the users have to do subtraction and drop down the next digit themselves. Learning whole calculation processes will make them master it in no time.

Math: Unknown is a helpful app for students who seriously want to improve arithmetic calculation skills.

Column Design (Part 6)

From Column Design Part 1 to 5, we talked about the formulas to calculate the critical buckling load. This time we're going to use the excel spreadsheet program to help calculate. Let's use the following design problem as an example.

The machine designer would like to calculate the allowable load for his steel column having rectangular cross section. The column has section 80 mm x 30 mm, and 380 mm long. It's proposed to use AISI 1040 hot-rolled steel. The upper end is pinned and the lower end of the column is inserted into a close-fitting socket and is welded securely as can in the picture.


To calculate the critical load for the column we need to do as following.

Solid rectangular section, 80 mm x 30 mm.
The area moment of inertia, I = 1/12 x 80 x 303 = 180000 mm4  -- The least I (for this case, around X-X axis) is used.
The cross sectional area, A = 80 x 30 = 2400 mm2
Then the radius of gyration, r = (180000/2400)1/2 = 8.66 mm
Since the column is pinned at the upper end and welded at the lower end, then the end fixity is fixed-pinned.
The practical value of constant K = 0.8 is used for this kind of end fixity.
The effective of the column, Le = KL = 0.8 x 380 = 304 mm
The slenderness ratio = Le/rmin = 304/8.66 = 35.1

The material AISI 1040 hot-rolled steel has yield strength (Sy) and modulus of elasticity (E) as follows.
Sy = 290 MPa
E = 207 GPa

Then we can calculate the column constant, Cc = (2p2 x 207x109 / 290x106)1/2 = 118.7

Because the slenderness ratio (35.1) is less than the column constant (118.7), the column is short. The J.B. Johnson formula should be used.

The critical buckling load becomes,\
Pcr = (2400x10-6) x 290x106[1-(290x106x35.12)/(4p2  x 207x109)] = 665571 N

With the safety factor N = 3, the allowable load for this column is
Pallow = Pcr/N = 665571/3 = 221.8 kN

As usual, mechanical design handbook provides free excel program that can help you solve your column design quickly. Please download the file for FREE at the link below.


Please make sure that macro is enabled so that you can run the program. Once the program is launched, (1) select the end fixity (2) enter values of cross section, column material and safety factor (3) Click calculate to see the result.

Download FREE Excel File of Column Design.
password: mechanical-design-handbook.blogspot.com

Comments

Post a Comment

Popular posts from this blog

Linear Actuators and Linear Motion

Mechanical energy is an area of science that is making strides every day. The study of how actuators produce mechanical motion by converting various forms of energy into mechanical energy is a source of great exploration. Science finds new ways to make use of actuators every day including for medical purposes. Many scientists believe that the more they study these seemingly simple machines, the more they will discover ways of helping mankind. The way in which a linear actuator works is that there is a motor that rotates a drive screw using a synchronous timing belt drive. Some linear actuators can also use a worm gear drive or direct drive. Whichever the choice, the turning of the screw pushes a drive nut along the screw, which in turn pushes the rod out and the rotating the screw in the opposite direction will retract the rod. According to the Association of Sciences, the drive screw is either an ACME or ball thread or is belt-driven which is what gives the machine its motion. A cov
Read more about this Mechanical Design Article »

Ball Detent Torque Limiter: Overload Clutch

Image
A torque limiter is an automatic overload clutch that provides machine protection and reduces repair time during jamming load conditions. This is done to protect expensive machines and prevent physical injuries. A torque limiter may limit the torque by slipping (as in a friction plate slip-clutch), or uncouple the load entirely (as in a shear pin). Ideally the torque limiter should be placed as close as possible to the source of the jam. This will allow the system inertia and torque to be quickly and effectively disconnected from the jammed section. The system can then be allowed to stop without causing further machine damage. A mechanical torque limiter will provide faster response times and better protection than typical electronic methods at high crash rates. There are several disconnect types available, but we will focus at the Ball Detent type . A ball detent type torque limiter transmits force through hardened balls which rest in detents on the shaft and are held in pl
Read more about this Mechanical Design Article »

Watt Straight-Line Mechanism

Image
Watt's linkage (also known as the parallel linkage ) is a type of mechanical linkage invented by James Watt to constrain the movement of a steam engine piston in a straight line. The idea of its genesis using links is contained in a letter he wrote to Matthew Boulton in June 1784. "I have got a glimpse of a method of causing a piston rod to move up and down perpendicularly by only fixing it to a piece of iron upon the beam, without chains or perpendicular guides [...] and one of the most ingenious simple pieces of mechanics I have invented." This linkage does not generate a true straight line motion, and indeed Watt did not claim it did so. Watt's straight-line mechanism is used in the rear axle of some car suspensions. It intends to prevent relative sideways motion between the axle and body of the car. Watt’s linkage approximates a vertical straight line motion more closely, and does so while locating the center of the axle rather than toward one side of the
Read more about this Mechanical Design Article »