rube goldberg project 2011 written report

SPH4U Physics 12

Independent Study Unit

| Rube Goldberg Machine Project: Raising a Flag

Akmal Farhan Ab Rahman

1007C10603

Mr Tan Swee Chuan, Period 2

Eddy Arief Zulkifly

1007C10605


Mohd Afiq Mohd Asri

1007C10609


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THE STEPS:

EXPLANATION OF ACTIVITY AND PHYSICS CONCEPTS/PRINCIPLES

Our Rube Goldberg machine project consists of 16 distinct steps. The final product of the

machine is raising a Malaysian flag. The machine encompasses various Physics concepts and

principles.

Step 1: Projectile motion from an incline

A marble goes down an incline. At the end of the incline, the marble goes

airborne momentarily before falling into the plastic bottle.

Physics concepts/principles::

- Along the incline, the marble experiences gravitational, frictional and

normal forces. The force of gravity is resolved into components parallel

and perpendicular to the incline.

- using the Principles of Conservation of Energy, the potential energy of

the marble at the top of the incline is converted into kinetic energy as the

marble rolls down the incline. The velocity at the end of the incline is

given as v = 2𝑔ℎ

- The marble undergoes projectile motion launched at an angle below

horizontal. The final velocity of the marble from the incline becomes the

initial velocity of the projectile.

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Step 2: Helix rotational motion

As the marble enters the plastic bottle, the

marble undergoes circular motion due to

the high velocity gained from the incline.

As the rotation approaches the bottom of

the funnel, it falls onto the mousetrap.

Physics concepts/principles:

- The circular motion is caused due to the

centripetal force supplied by the normal

forces acted upon the marble by the walls

of the plastic bottle.

- As both centripetal force and gravitational force is acting upon the marble, the marble

experiences a helix shaped rotational motion.

- At the bottom of the funnel, the marble free falls onto the mousetrap.

Step 3: Mousetrap

The marble fell onto the mousetrap. The

mousetrap snaps and pulls the string

horizontally.


- The elastic potential energy stored in the spring of the mousetrap supplies the restoring

force of the spring. The strong restoring force is larger than the tension in the string, Fs > T,

causing the string to be pulled.

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Step 4: Series of pulleys

The pulled string undergoes a series of high friction pulley

system. The string pulls the lever.


- The tension in the string provides the force to pull the

lever. As the string is pulled across high friction pulleys,

energy is loss to overcome the friction, hence lowering the

force. The energy loss is approximately ½ for each pulley.

As there are 3 pulleys along the system, the force in the

string, T to pull the lever is approximately 1

2𝑛 =

1

23 =

1

8 of the

force supplied by the mousetrap.

Step 5: Knock the marble

The string pulls the lever. The lever turns and hits the

large marble.


- The lever is a first class lever, where the fulcrum is

in the centre.

- The string pulls the lever at from an angle θ ≈ 90°.

The torque produced by the lever is given as 𝜏 =

𝐹 𝑟 sin𝜃. As the F = T and sin 90° = 1, 𝜏 = 𝑇 𝑟 ,

where r is the distance between the fulcrum and the

force.

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Step 6: Split steps – Newton’s cradle and opening the trapdoor

The large marble collides with another large marble. Both marbles hit the Newton’s Cradle and

the falls into a basket. The basket pulls the strings across a pulley that opens the trapdoor in Step

9.


- The inelastic collision between the marbles obeys the Principles of Conservation of

Momentum.

- The collision with the Newton’s Cradle is elastic.

- The gravitational force acting on the marbles as it falls into the basket is greater than the

tension in the strings, mg > T. A net force acted on the basket and the trapdoor, causing the

basket to move downwards and trapdoor to move upwards. The trapdoor opens with the lower

acceleration as the basket, as force due to tension is also used to overcome friction of the pulley.

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Step 7: The see-saw

The Newton’s cradle hits a

domino piece, which falls

onto a makeshift elastic ruler

see-saw. The see-saw tilts a

horizontal runway and

releases a marble along the

incline into the corrugated

tubing.


- The kinetic energy from the Newton’s marble is transferred to the levers.

- The marble rolls down along the incline.

Step 8: Corrugated tube

The marble rolls inside the corrugated tubing and exits

into a semi-circular channel, which leads to Step 10.


- The motion inside the corrugated tubing causes

energy loss to the marble due to the high frictional

force acted by the walls of the tubing. This reduces

the speed of the marble before it goes into the channel.

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Step 9: Marbles and plane with obstacles

When the trapdoor moves upward, it allows 9 marbles to move down the transparent incline

plane. Using gravitational potential energy, the 9 marbles move down the plane, knocking the

vertical pole obstacles along way and fall into a slightly-inclined horizontal track at the end of

the plane. The marbles then follow down the inclined path onto the semi-circular channel.


- Along the incline, the marbles experiences gravitational, frictional and normal forces. The force

of gravity is resolved into components parallel and perpendicular to the incline.

- using the Principles of Conservation of Energy, the potential energy of the marble at the top

of the incline is converted into kinetic energy as the marbles are released and roll down the

incline. The velocity at the end of the incline is given as v = 2𝑔ℎ

- The collision with the obstacles causes loss in mechanical energy due to work done on

negative direction.

- The sudden change in direction and inclination angle between the plane and the horizontal track

causes the magnitude of velocity of the marbles to reduce greatly.

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Step 10: Marble accumulation

The marble from the Step 8 and the nine marbles from Step 9

are channeled through the semi-circular channel and are

directed into a narrow inclined track. A small slit is cut at the

side wall of the track. As the marbles accumulate in the track,

the first nine marbles fill in all the spaces of the track, causing

the last marble to fall through the side of the track wall.


- Along the incline, the marbles experiences gravitational,

frictional and normal forces. The force of gravity is resolved

into components parallel and perpendicular to the incline.

- the mass of the nine accumulated marbles is greater than the last marble (9m >> m), causing it

to exert a force on the last marble upon collision.

- the marble momentarily experiences free fall.

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Step 11: The slippery satin cloth

The marble falls onto a stretched satin cloth. The cloth absorbs the impact of the fall, and then

slides down the smooth cloth. The marble is launched airborne over a gap, before landing on

another platform of stretched satin cloth.


- The stretched cloth absorbed the force from the falling marble as it is slightly deformed, hence

increasing the interaction time, Δt between the marble and the cloth. Impulse, J, is constant

during contact as it is affected by the change of velocity of the marble before contact. Reducing

the force is important to avoid the marble from bouncing off.

- The smoothness of the cloth greatly reduces the frictional force acting on the marble as it

slides down.

- As the marbles reaches the gap, it is launched to a projectile motion before landing on another

cloth. The cloth again absorbs the force and avoids the marble from bouncing.

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Step 12: Chain reaction

The marble rolls down the cloth and hits the first trigger, moving the first marble from rest. The

marble knocks the next trigger, and releases all the subsequent three marbles. The last marble

rolls down the incline before it stops on the steel wire loop, and falls onto the track below it.


- The momentum from the rolling marble is transferred through the triggers and the marble. The

kinetic energy loss during the inelastic collision between the marbles and the triggers is

compensated by the kinetic energy gained as the marbles rolls down the incline.

- The last marble experiences a large change of momentum at the end of the inclined track as it

is abruptly stopped by the steel wire loop. The change in velocity becomes Δv = 0 –vi. The

marble momentarily undergoes free fall.

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Step 13: Sideways motion transfer

The marble rolls along the track and hits the pivot. The pivot stops the marble. The force by the

marble is transferred at an angle by the pivot to the stationary large marble. The large marble

rolls down the steep incline to the banked curve.


- The pivot transfers the initial force, Fi from the marble, to the large marble. The resultant

force (assuming energy absorbed by the pivot is negligible) is given as |Fnet|2 = |Fi|

2 + |Ff|

2 –

2|Fi||Ff| cos θ, at an angle θ which is the bend angle of the pivot.

- The final kinetic energy of the marble is given as Ekf = Epi + Eki + W, where work done is the

energy transferred to the marble by the pivot.

- Along the steep inclined track, the large marble experiences gravitational, frictional and normal

forces. The force of gravity is resolved into components parallel and perpendicular to the

incline.

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Step 14: The banked curve

The large marble undergoes semi-circular motion as it corners via the banked curve. The large

marble then rolls along the horizontal track and knocks the bottom of the long vertical lever.

Physcs concepts/principles:

- The banked curve provides the centripetal force to allow the marble change its direction. The

velocity of the marble is given such that v = rg tan θ.

- The kinetic energy from the marble is transferred from the bottom of the lever to the top of the

lever.

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Step 15: Long vertical lever and horizontal see-saw

The vertical lever pulls back and releases the horizontal see-saw. The horizontal see-saw tilts

towards the weight.


- The vertical lever holds the horizontal see-saw with a small frictional force. As force is

applied on the vertical lever by the large marble from Step 14, the frictional force is overcome

and releases the horizontal see-saw. The see-saw (first class lever) tilts towards the load i.e the

weight.

A k m a l , E d d y & A f i q | 13

Step 16: Raising the flag

The weight falls downwards and pulls the

string down across the pulley. The flag is

raised upwards.


-This step is based on the concept of an

Atwood Machine where 2 masses are

connected to the end of a single string. The

mass with a higher weight will be pulled

downward as the downward force

experienced; gravitational force is higher

than the tension of the string, mg > T. As a

result, the weight goes down with a

constant acceleration due to gravity. At the

same time, the mass with the lower weight

will move upward with certain

acceleration. In both cases, both objects

experience the same tension however, since the masses of each object are different, they would

also have different accelerations, as Fweight = m(g+a) and Fflag = m(g-a) and mweight > mflag.

A k m a l , E d d y & A f i q | 14

Problems Faced and Solutions/Modifications

Our project is based on a whole original concept of combined contraptions involving many

physics principle which at most time seemed easy to make but we realize that in the real world

everything required calculation and testing. The final design of the project has deviated much

from the original plan however; we believe that it was worth it as most of the original designs

were problematic and hard to design. While constructing the contraptions, we encountered many

problems and we solved the problems along the way instead of just adding steps and piling the

problem which in long term is beneficial.

Problem #1:

A wobbly wooden support for Step 1.

Due to the fact that the support system for the first step is wobbly and it’s fragile, we found out

that screwing/nailing the wooden pillars are weak. We used wood glue to attach the support

system to the base. Furthermore, we added an extra support pillar from the original pillars to the

wall.

Problem #2:

Inaccurate Centripetal Force trajectory in Step 2.

We wanted the ball to land into the plastic bottle at an angle and therefore making the marble

spin as long as possible in the bottle. We used a bottle with no patterns in it (such as coke

bottles). To increase the centripetal force, we had to estimate the position of the bottle. So we did

more than 40 tests to make sure the rotational motion of the marble was to our expectations.

Problem #3:

Marble shoots out at a random direction from the plastic bottle in Step 2.

To overcome the problem, we added a channel made out of paper so that the marble would land

directly on the mousetrap (which is the next step). To ensure that the marble always triggers the

mousetrap, we added a platform above the trigger, which will be lowered onto the trigger every

time the marble falls onto the platform.

Problem #4:

Mousetrap in Step 3.jumps up and down and affects tension of the string

When the mousetrap is not at a fixed position and moves around (because the spring force is

strong), the tension of the spring which is on the next step is greatly affected – not being able to

provide the maximum force. To overcome this, we glued the mousetrap to the base using wood

glue and we nailed it to fix its position.

A k m a l , E d d y & A f i q | 15

Problem #5:

The tension of the string in Step 4 was not strong enough to pull the lever up.

The solution to this is that we placed several brackets at strategic locations on the wall as to

provide maximum tension so that the lever is able to be lifted up at a reasonable force (more than

enough to move the marble). Also, instead of pivoting the lever to the wall using nails, we

decided to glue the lever to a door hinge which has less friction, allowing more force to be

transferred to the lever.

Problem #6:

Constructing a Newton’s cradle for Step 7.

A retail Newton’s cradle costs in excess of more than a few hundred Ringgit which was out of

our budget. Using our creativity we managed to make our own mini newton’s cradle by

encapsulating 3 marbles with metal wire. The wire acts as a supporting frame to tie the rope on

the marble to the overhead beam above it.

Problem #7:

Newton’s cradle in Step 7 did not swing properly.

The solution was to align the marbles in such a way that they are at their closest distance and are

exactly parallel to each other. To further strengthen this, we taped the exact positions of the

string to ensure the string did not change position due to subsequent trials.

Problem #8:

The marble in Step 7 was stuck at the funnel and did not fall into the corrugated

tube.

The solution was to tape pieces of card to form inclines that directs the marble straight into the

tube.

Problem #9:

Trapdoor for Step 9 did not open when the basket was pulled down.

The solution was to shorten the trapdoor such that it no longer depends on the slits to hold it in

place, instead only depends on the weight of the marbles. Therefore, the door only experiences

friction with one surface instead of two surfaces.

Problem #10:

Marbles in Step 9 move too fast that they flew off the plane.

The solution was to build a barrier using paper cups covering the end of the incline plane.

A k m a l , E d d y & A f i q | 16

Problem #11:

There is no proper method to channel the marbles from Steps 8 and 9 to Step 10.

The solution was to construct a semicircular canal using paper cups. Semicircular shape was

chosen instead of tubular shape because it channels the marble properly while not obstructing us

to make any adjustments.

Problem #12:

Marble did not slide down the cloth in Step 11 when the marble landed on it.

The solution was to stretch the cloth using chopsticks and wires placed at strategic spots.

Problem #13:

Last marble from Step 12 got stuck between the steel wire loops.

The solution was to enlarge the size of the loop, and to form a wall at the sides of the track below

the loop using mounting board to avoid the marble to run off-track.

Problem #14:

The large marble bounces off as it reaches the bottom part of the banked curve for

Step 14.

The solution was to add an extra ramp using cardboard to create a smoother path transition from

the inclined track to the banked curve.

Problem #15:

The flag was not raised after the weight is released.

The solution was to adjust the pulley system of the flag at the beginning of every trial to ensure

the string lies on the pulley wheel and not stuck between the axles. The mass of the

counterweight tube is increased by adding marbles into the tube.

A k m a l , E d d y & A f i q | 17

Skills Learned While Doing Project

Throughout the construction of our Rube Goldberg machine, we gained many useful technical

and interpersonal skills that are very valuable for our development as future leaders and

engineers.

1. While constructing our Rube Goldberg Project, an important skill that we gained was

learning to make the best out of everything. We did not have a relatively high budget

for our project and most of the tools used were mostly from friends or leftover items

from home. Rather than buying items from stores, we instead learned the art of

recycling old materials from previous projects as well as rummaging in the garbage

for useful items. For example, the red cloth for the slide came from Akmal and

Eddy’s Calculus and Vectors project while the black tube which brings down the flag

came from a model ship which was left lying beside garbage inside the Taylors

Wisma Subang Jaya building.

2. Another important skill that we learned was connecting theory to practice. Students

are mostly taught about the theoretical aspects of Physics but are rarely exposed to the

real life application of Physics concepts in daily life. Banking curves were easy to

understand in the textbook, but in real life they are definitely much harder to recreate.

This was due to additional factors that were needed to be put into consideration such

as the orientation of the marble ball as it moves on the curve, the effect of gravity and

friction on the marble as well as the direction the marble moves while travelling on

the banked curve.

3. The Rube Goldberg project also helped us develop our divergent thinking skills.

Humans are normally taught that there is only one way to do things. For example, to

make a marble move from one place to another, you would require cable or anything

that can channel the marble in a particular direction. However, from the project we

learned that this need not be the case. For example, rather than using a cable to

channel the last marble to the multilevel marbles step, we instead used red cloth

which functioned like a ramp. To ensure the marble fell in a particular direction, we

adjusted the position and height of the cloth to ensure the marble jumped with a

particular angle. As the marble dropped from the cloth, it gained kinetic energy and

jumps of the cloth, landing exactly around pivot which activates the next step. Thus,

we creatively solved the problem of moving the marble around the base while

showing a few physics concept at the same time.

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4. Lastly and most importantly, while completing our Rube Goldberg project, we

learned the value and skill of teamwork. Like in any football match, a team of players

will always win a match rather than a group of individuals. Everyone in the group

offered something different to the table whether it was Akmal’s creativity, Afiq’s

craftsmanship or Eddy’s management skills. A strong team composes of people with

different skills sets rather than people of similar strengths and backgrounds. We as a

team were able to compensate each other’s weaknesses and produce the best quality

work possible.

rube goldberg project 2011 written report

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