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MECHANICAL ENGINE
OVERALL EXPECTATIONS power was replaced by a massive ballast box to act
For a detailed list according to grade level, see as a counterbalance and force of propulsion.
pages 6 and 7.
If students are using twigs or sticks, snap the
ENGAGE! pieces rather than sawing them. The use of twigs
Start by asking students to define an engine. No and sticks in this challenge adds a touch of authen-
doubt they will come up with a modern version ticity and could lead into a discussion of the mate-
such as: “a machine for converting thermal energy rials available 1,000 years ago.
into mechanical energy or power to produce force
and motion.” Ask them to think more primitively Divide the class into groups of two to four
and discuss how a catapult is an engine. Look to a students.
good dictionary for a definition of an engine (a
children’s dictionary may be too specific). Discuss GLOSSARY
various kinds of engines. For useful websites on Catapult: a stone-throwing engine powered
early engines, go to: http://www.middelalder by teams of soldiers pulling on ropes
centret.dk/warengines.htm#top.
Trebuchet: a heavy stone-throwing engine
powered by a large counterweight
BACKGROUND
This exercise takes students back more than 1,000 Mangonel: a light stone-throwing engine
years to learn how people used the laws of physics powered by a skein of twisted rope
and good construction techniques to develop ways
to move large rocks over great distances very
quickly. Medieval siege engines include catapults, MATERIALS
trebuchets and mangonels, all variations on the clothes peg or clip scissors
mechanical engine to be built here. cup hooks small sticks or branches
elastic bands string
TEACHER INFORMATION eye hooks tape
The students will build a siege engine. Early engines glue gun teaspoon
were powered by hand: people pulled a rope to hobby saw wire
accelerate the throwing arm. Later, engine man- knife wire cutters
plastic spoons wooden dowels
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MAKING A MEDIEVAL SEIGE the catapult. For safety reasons, an arm length of
ENGINE not more than 30 cm is suggested, and you may
To build the main frame of the siege engine, stu- wish to limit the number of elastics used.
dents will make two mirror image sides. Place a
24-cm stick on a bench parallel to the edge, then RESULTS
place a second stick (18 cm) perpendicular to the Students test the mechanical efficiency of the
first about one-third the distance from one end. machine. How many times its length can the cata-
Glue and bind them together with string or wire. pult throw an eraser?
Triangulate (brace) the upright with a smaller stick
as shown in the photo.
Repeat the process for the
opposite side. Stand these
finished sides upright and
place them approximately 16
cm apart.
Make four 18-cm-long cross-
bar sticks and secure them
to the side frames with glue
and wire. Position two at the
rear, one at the front and
one at the top of the
uprights as shown in the
photo. Screw a cup hook
into each upright pointing
toward the rear of the
frame, 6 cm from the base.
(This is to accept the pivot
on the throwing arm.)
To make the throwing arm,
cut a 20-cm-long stick and place a chopstick pivot EXTENDING THE ACTIVITY
4 cm from one end to make a cruciform (cross). The stored-up energy in the catapult’s spring need
Glue and bind them together. Glue and bind a tea- not be used to hurl something. Gears and wheels
spoon to the long end of the cruciform and place can be added to the catapult to leverage the
an eye hook into the shorter end. Place the pivot engine’s energy. To make a catapult car, wind string
into the cup hooks on the uprights. around an axle with wheels and attach the string
to the throwing arm. As the arm is released, it will
Stretch elastic bands from the eye hook on the pull the string which turns the wheels.
throwing arm to the rear of the catapult as shown
in the photo.Tie string to the spoon end of the
throwing arm, then fashion a quick-release trigger SAFETY NOTE
(e.g., clothes peg) to the back of the frame. Load Use a designated test area, such as the
the spoon with an eraser and fire! gym or hallway. Students should wear
Experiment with the design to improve efficiency. safety glasses to protect their eyes from
The length of the throwing arm and the number of the projectiles being launched.
elastics used will govern the throwing power of
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HEAT ENGINE
OVERALL EXPECTATIONS
For a detailed list according to grade level, see TEACHER INFORMATION
pages 6 and 7. The heat engine works on the principle of heat
convection. As the water at the bottom of the
BACKGROUND coils heats up it rises to the top of the coils push-
Heat is the energy of moving molecules. Because ing the water ahead of it down to the bottom of
heat is energy, it can be changed into other forms the coils. This then heats up the new cool water,
of energy. Heat can power cars and planes, turn repeating the cycle until the warm water is forced
turbines to make electricity and much more. out of the outlet, pushing the boat along. To get
the water into the tube initially, it will be necessary
The Drinking Bird, that well-loved childhood toy, is to prime the coils by sucking water into them
an excellent example of a heat engine. It uses using a straw or plastic pipe.
water as its fuel. The energy available from the
evaporation of one gallon of water is approximate-
ly equal to the available energy from burning one GLOSSARY
half gallon of gasoline. Convection: the circulatory motion that
occurs in a fluid at a non-uniform tempera-
There are two main kinds of fuel-burning heat ture owing to the variation of its density
engines: external combustion, such as steam and the action of gravity
engines, where the fuel is burned outside the
engine’s moving parts, and internal combustion,
such as jet engines and car gasoline engines, where Boiling water to make steam to drive a mechanism
fuel is burned inside. is dangerous in the classroom. For safety reasons,
this challenge uses a tea light candle as the heat
In the 18th and 19th century, the power that drove source.Warn the students that this is not a speed
the Industrial Revolution was the steam engine. Its boat; they should test it in a basin or water table
uses varied from driving the great machines of and exercise lots of patience.
industry to transportation in the forms of locomo-
tives, steam ships and traction engines. Steam Have groups of two to four students build an
engines are still used in present-day nuclear power external combustion engine to power a boat.
stations. In this application decaying nuclear fission
is the fuel source that drives the steam engine.
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Proceed to form four or five
coils around the handle, bring-
ing the free end of the copper
tubing down parallel to the
other end. Measure 4 cm from
each end of the tubing and
mark with a pen.
Using the end of your thumb,
bend the tubing to a large
radius 90-degree L shape at
the bottom of the coils. One
end of the tubing will be the
MATERIALS engine’s intake; the other will be the outlet and will
2 small plastic water bottles point to the back of your boat. (Check photo for
4 chopsticks or wooden dowels details.) Fix the copper coils to the deck, as
50 cm thin copper tubing (found in hardware shown, leaving space beneath for the candle.
stores, used for repairing refrigerators)
broom handle RESULTS
elastic bands Students evaluate the design and identify modifica-
flat piece of wood 15 cm x 3 cm x 0.5 cm thick tions to improve effectiveness while learning how
glue gun energy is transferred to a specific output.
pliers
small saw
EXTENDING THE ACTIVITY
tea light candle
What other designs can the class come up with?
water table or water tank
What other materials can be used to build the
boat? The coil can be attached to boats of other
MAKING A HEAT ENGINE BOAT design. Ask the students to discuss what other
The heat engine is a simple copper coil arrange- fuels could be used. Could the same heat coil be
ment. To make the coils, you will need a broom used to build a heat turbine (i.e., a Christmas orna-
handle to use as a forming guide. Note: If copper ment that turns when a candle is burned)?
tubing is bent at a right angle with a sharp corner, the
tubing will kink and collapse, creating a blockage.
SAFETY NOTE
Measure 10 cm from one end of the copper tube This is an open flame activity. Please
and mark with a pen. This is the point at which
ensure that students respect the fact
you will start bending to make the coils. Place the
copper tubing across the broom handle at 90 that they are working with fire.
degrees, with the short end pointing down.
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CHEMICAL ENGINE
OVERALL EXPECTATIONS plunger). The piston starts at the top of the cylin-
For a detailed list according to grade level, see der. The piston moves down and draws a tiny
pages 6 and 7. droplet of gasoline and air into the cylinder. The
intake valve closes (cover the tip of the syringe
ENGAGE! with your finger) and the piston pushes up into the
Invite students to imagine what our life would be cylinder to compress the fuel/air mixture. A spark
like without chemical (combustion) engines. More ignites the gasoline, which explodes, forcing the
than 100 years ago, external combustion engines piston down. The exhaust valve opens (uncover
used a variety of fuels to produce steam-powered the tip of the syringe) and the piston pushes up
boats and trains (see Challenge 2). Reciprocating into the cylinder, forcing the exhaust to go out the
internal combustion engines now power cars, tail pipe. The exhaust valve closes and the intake
buses, lawnmowers and snowmobiles. Gas turbines valve opens. The cylinder is ready to repeat the
power jets. Rocket engines launch satellites and cycle over and over. There is a great moving dia-
the space shuttle into orbit. What is combustion? gram of a working piston and cylinder at
See Engine and Energy Basics on page 5. www.howstuffworks.com/engines.htm.
What fuels are used in these four types of com- The reciprocating motion of the piston is con-
bustion engines? What machines are powered by verted to rotational motion in the crankshaft
each of these engines? What are the effects of through the connecting rod. The connecting rod
combustion engines on the environment? Use such joins the piston to the crankshaft with a pivot at
websites as www.howstuffworks.com to gather
information on combustion engines. Additional GLOSSARY
websites are listed under Teacher Resources on Reciprocating Motion – movement of an
page 23. object alternately backward and forward in a
straight line (e.g., moving a piston up and down
BACKGROUND in a cylinder)
Most of today’s automobiles use the combustion of
Rotational Motion – movement of an object
a liquid fuel, such as gasoline, to power a recipro-
in a circular manner about an axis (e.g., rotat-
cating internal combustion engine. Imagine an
ing a wheel)
engine cylinder with a piston (like a syringe with a
13
each end so that the connecting rod is free to oxygen at high temperature and pressure (in
change angles as the piston moves up and down engine cylinders) to produce nitrogen dioxide.
and as the crankshaft rotates. This rotational Some hydrocarbons remain in a vaporized (gas)
motion is transferred to the axle and wheels to state.Water is harmless as is carbon dioxide in
propel the vehicle. The Newton’s Apple website small amounts. In large amounts, carbon dioxide
has a good overview of how a car engine works, (also known as the greenhouse gas) is blamed for
including directions on how to build a model of a global warming. Sulfur dioxide combines with
piston/crankshaft system. See www.pbs.org/ktca/ water in the air to produce acid rain. Nitrogen
newtons/15/carengines.html. dioxide and the remaining hydrocarbons react in
the presence of sunlight to produce smog.
Gas turbine engines are powered by burning a
gaseous or liquid fuel, such as propane, natural gas, TEACHER INFORMATION
kerosene or jet fuel, in pressurized air. The hot, The students will build a wheeled vehicle, which is
pressurized gas that is produced spins a turbine. driven by a reaction (water rocket) engine. The
The linear motion of the exhaust gas is convert- fuel is baking soda and vinegar which reacts chemi-
ed to rotational motion in the turbine. Gas turbine cally to produce an exhaust gas of carbon dioxide.
engines are smaller than a reciprocating engine of The mass of the exhaust is increased (to increase
the same power; however, they are much more the forward thrust of the vehicle) by adding water,
expensive.This and the fact that gas turbines use which is forced out of the neck of the bottle by
more fuel when idling are the main reasons that the pressurized carbon dioxide.
they are not used in motor vehicles.
Ask groups of two to four students to design and
build a wheeled vehicle with a water rocket engine
GLOSSARY
capable of travelling three metres.
Linear Motion – movement of an object in
a straight line (e.g., rolling a ball) MATERIALS
2-litre plastic pop bottles
Rocket engines operate on a different principal adhesive
than the other types of engines, which produce axles (dowel, coat hanger wire)
rotational energy. Rocket engines are driven by baking soda
Newton’s second law which states that “for every boxes
action there is an equal and opposite reaction”. buckets
When rocket fuel (liquid or solid) burns, it pro- cardboard
duces a hot, high-pressure gas. The mass of the construction kits, such as K’NEX
exhaust gas discharged from the back of the rock- cutting tools
et causes the rocket to fly in the opposite direc- funnels
tion (linear motion). A good demonstration of this glue guns
principal is the release of an inflated balloon.The plastic
release of air out the back of the balloon causes safety glasses
the balloon to fly forward. scissors
screwdrivers
Liquid fuels, such as gasoline, diesel, kerosene and screws
fuel oil, and such gaseous fuels as natural gas and string
propane, are hydrocarbons made mostly of carbon vinegar
and hydrogen with sulfur also present. When gaso- water
line is ignited, the carbon, hydrogen and sulfur wheels (manufactured or homemade; juice can lids
react with oxygen in air to produce carbon diox- work well)
ide, water and sulfur dioxide, which are all gases. wood
Nitrogen, which is also present in air, reacts with
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MAKING A LAUNCHER
Join the two boards in the shape of a T, using the
door hinge as a connector. Drill a 1/4” hole, in the
center of the horizontal part of the “T”, 1 cm from
the edge of the hinge. Use No. 10 screws.
One launcher shared by class:
Put the bolt through the stopper (narrow end
2 pieces 1” x 4” wood approx. 30 cm (12") long
first), the hole in the wood (from the side to which
1 door hinge
the hinge is not attached), and the washer. Attach
4 1 1/2" (3.8cm) corner braces (L-brackets)
the nut. Students may have to drill the top hole
1 1/4” x 2 1/2" (6.2 cm) bolt, washer and nut
larger in each of the L-brackets so that the spike
1 #3 1-hole rubber stopper (available from
can slide in and out easily.
school science supply catalogues)
6 No.10 screws Open the hinge so that the two pieces of wood
8 No.6 screws are relatively flat with the stopper pointed up.
3 15 cm (minimum) spikes or aluminum tent Position a 2-litre pop bottle on the rubber stop-
pegs per. Position the four L-brackets so that when a
3 m strong cord spike is passed through the top holes of the L-
drill and bits bracket, the spike sits over the lip on the neck of
screwdriver the pop bottle (see photo above). It is best to
15
attach one L-bracket at a time and retest the posi- A mess will be created when these vehicles are
tioning before attaching the next L-bracket. Use launched, so it is best to do it outdoors. Choose a
No. 6 screws. smooth surface into which you can hammer a
spike to hold the launcher in place (e.g., a baseball
Cut a 30 cm length of cord. Melt the ends with a
diamond). If this is not available, use a transition
match or lighter so they don’t fray. Tie each end
area (e.g., position the launcher on the grass right
to a spike. Tie the remaining cord to the middle of
next to a paved area where the vehicle can run).
the 30 cm cord. Drill a hole in the center of the
Have some sessions outside during the construc-
board that is the vertical part of the T. It should be
tion phase of the project so students can test their
large enough to accommodate the remaining spike.
vehicles for design modifications.
The teacher and/or a group of students should set
MAKING A WATER ROCKET
design standards such as vehicle size, dimension
ENGINE VEHICLE limits, time to complete the prototype and testing
In the photographs (on page 15), one vehicle is period, vehicle weight restrictions and materials or
made of a clementine box with juice can lids for any other criteria the group decides to impose.
wheels and one is constructed of K’NEX. (Keep in The group can increase the complexity of the
mind that smooth wheels offer less resistance than activity by adding more criteria.
textured wheels.) Both vehicles are built around a
2-litre pop bottle engine. RESULTS
The pop bottle must be angled in the vehicle so Students repeatedly test their designs and observe
that the water will be pushed out by the pressure the way their vehicles behave.They record their
of the gas. However, it is desirable to keep the difficulties and describe how they were able to
angle as low as possible to maximize the horizon- correct design problems.
tal thrust. Have the students experiment with their
pop bottles and water in a sink (or outside) to EXTENDING THE ACTIVITY
determine the optimum angle. An evaluation committee could award certificates
of merit to vehicles that were able to complete
LOADING A CHEMICAL ENGINE certain tasks. Students can experiment with differ-
• Use 500 mL water, 4 heaping soupspoons baking ent amounts of water, baking soda and vinegar to
soda, 125 mL vinegar maximize the distance the vehicle will travel.
• Designate "wet" and "dry" funnels. They are not
interchangeable.
• Pour water through the "wet" funnel into the
pop bottle.
• Pour baking soda through the "dry" funnel into
the pop bottle.
• Have the launcher ready to attach to the pop
bottle.
• Pour vinegar through the "wet" funnel into the
pop bottle. SAFETY NOTE
• Immediately, insert the rubber-stopper on the The launch MUST be done outside.
launcher into the bottle.
The engines will launch with great force.
• Insert the two spikes through the L-brackets to
hold the bottle in place. Make sure the bottle is securely fastened to
• Take as much time as you need to position the the vehicle. If the pop bottles detach, they
launcher and vehicle. can fly a significant distance. Make sure the
• Hammer the third spike into the ground and track is clear of students and do not launch
make sure the track is clear.
toward windows.
• Pull the cord and "let ’er rip".
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