Physics: Investigation - Machines

The Workable Procedure

We were given lego construction kits to build a simple machine that could show some ideas of mechanical advantage. We decided to invent something / play around and investigate the lego pieces. Later we used the examples provided and worked as a group to construct a simple windmill/fan. It took us no time to do so, but we were amused at its motion. The design is very much similar to the example provided (PTO).

How it Works

The main components for this machine involve the 8 and 40 mm in diameter gears. The work input (by manual rotating) spins the 40mm gear; as it rotates the 8mm gear that is connected to the fan (output).

Observations

The machine operated successfully. The direction of the input moves oppositely to the direction output, because only 2 gears were used in this. It was seen that the speed of the fan moved faster than the manual rotation, thus a small breeze was felt nearby!

Results

 Diameter (d) Revolutions (R) Circumference (R*d) Distance Moved (R*d) Input 40mm 1 125.7mm 125.7mm Output 160mm 5 502.7mm 2513.3mm Input 40mm 2 125.7mm 251.3mm Output 160mm 10 502.7mm 5026.5mm

As we can see, a pattern is visible...

To calculate the mechanical advantage, we can use the following formulas…

M.A =     Output Force             AND           M.A. =          Load     _
Input Force                                                Applied Force

In our investigation, we decided to use                M.A =    Input Distance *
Output Distance

* because this machine mainly deals with distance moved.

Therefore, the mechanical advantage  =      40           =                OR       0.05
5 X 160               20

Analysis of Results

The mechanical advantage was calculated to be 0.05. Since the fan/output expends more distance and less force, the M.A. is less than 1. Due to the conservation of energy law: no energy is created or destroyed. So the of work input (force x distance) equals output (force x distance). The products can be changed, ie; increase force, decrease distance and decrease force, more distance. Therefore, forces can multiply… In our machine, the input work has less rotational distance, but it needs more force to rotate it. The output work has more rotation, at the expense of a smaller force.

Talking about the efficiency, (which is harder to measure) the useful work output must be calculated. Because it is not possible to have a 100% efficient machine, the lost energy / percent may result in friction and the generation of heat and wind energy. Therefore more input force maybe needed to overcome friction, compared to the theoretical force needed. This means it will need more input work, as we look back at the equation, the final/actual mechanical advantage will be higher than the theoretical one!

Synopsis

Using the lego sets, we designed a windmill machine so that could demonstrate a mechanical advantage. Consist of 43 parts, the main components were mainly the gears.

The data recorded were the input distance (manually rotated) and the distance of output (the spin of the fan). It was then plugged and chugged in the formulas: M.A. = input distance / output distance. The mechanical advantage in our investigation was 0.05.

Since we are trying to increase output distance, the M.A. is a low figure. Mechanical advantage is the advantage of lifting a heavy load by increasing the distance to reduce the force needed. In our machine, it is the opposite. Since we want to make speed/wind, we are putting less distance and large force to produce a larger distance and less force. The total input work is always the total work output (conservation of energy). This explains why when we increase one, we decrease the other; but the product of f and s is always the same at both ends.

Throughout this investigation, error was minimal. The errors in our machine were friction, loss of energy or generation of wind energy. This meant that more force/work is needed to spin the gears to overcome friction. The actual M.A would differ to the theoretical one (it would be higher), and the efficiency is lesser.

I learnt that life is much easier with machines, and life is more fun in kindergarten.