Why Does Metal Expand When Heated? (Mr. Wizard)
Summary
TLDRThis video script documents an experiment demonstrating the thermal expansion of metals. A metal wire is heated over a wooden block with thumb tacks, causing the wire to expand and rotate a straw pointer. The experiment then escalates with a bar being heated with a blowtorch, causing it to lengthen and tighten a metal piece within it. Upon cooling with water, the bar contracts, showcasing the immense energy and strength in molecular motion due to temperature changes, ultimately breaking the bar in half.
Takeaways
- π₯ The script demonstrates the concept of thermal expansion in metals, showing that they get longer when heated and shorter when cooled.
- π A wooden block with thumb tacks and a metal wire resting on a needle is used to visually represent the expansion and contraction of metal due to temperature changes.
- π―οΈ The experiment involves lighting candles under the metal wire to heat it, causing the wire to expand and rotate the straw pointer, indicating the expansion.
- π¬ The experiment is designed to magnify the small movements of the metal wire, making the thermal expansion observable.
- β οΈ Safety is emphasized, with the use of safety glasses and caution while handling the blowtorch.
- π§ The script describes a method to tighten a metal bar using heat and then secure it to prevent slack when it cools down.
- π₯ The use of a blowtorch to heat the center of the metal bar is part of the experiment to show how metals expand when heated.
- π·ββοΈ The experimenters take turns heating and tightening the metal bar, illustrating the process of thermal expansion in a practical way.
- π§ The script mentions pouring water on the heated bar to demonstrate the rapid contraction as the metal cools.
- π¨ The experiment concludes with a dramatic demonstration where the cooled and tightened metal bar breaks, showing the strength of the molecular action during thermal changes.
- π§ The script aims to educate about the energy contained in the movement of molecules and how it affects the physical properties of materials.
Q & A
What happens to the length of metal when it is heated?
-When metal is heated, it expands and gets longer due to the increased kinetic energy of its molecules.
What happens to the length of metal when it cools down?
-When metal cools down, it contracts and gets shorter as the kinetic energy of its molecules decreases.
What is the purpose of the wooden block, thumb tacks, and metal wire in the experiment?
-The wooden block with thumb tacks and the metal wire serve as a simple apparatus to demonstrate the thermal expansion of metal by observing the rotation of the wire and the straw pointer.
Why does the straw pointer rotate when the metal wire is heated?
-The straw pointer rotates because the metal wire expands when heated, causing the wire to exert force on the thumb tacks and rotate the pointer.
What role do the candles play in the experiment?
-The candles are used as a heat source to warm the metal wire, causing it to expand and rotate the straw pointer.
Why is the expansion of the metal not very noticeable in the experiment?
-The expansion of the metal is not very noticeable because the setup is designed to magnify the effect through the rotation of the wire and straw pointer, making small expansions more visible.
What happens to the straw pointer when the candles are removed and the metal cools down?
-When the candles are removed and the metal cools down, the metal contracts, causing the straw pointer to return to its original position, indicating the metal has shrunk.
What is the purpose of the second experiment with the bar and the hole?
-The second experiment aims to demonstrate the significant force generated by the thermal expansion of metal, which can be strong enough to tighten a piece of metal to the point of breaking.
Why is it necessary to wear safety glasses during the second experiment?
-Safety glasses are necessary to protect the eyes from any potential hazards, such as flying debris or sparks, that may occur while using the blowtorch.
What is the expected outcome when water is poured on the heated bar in the second experiment?
-When water is poured on the heated bar, the bar is expected to contract rapidly due to the rapid cooling, which may cause the bar to break due to the stress caused by the sudden change in temperature.
How does the molecular action of heating and cooling affect the strength of the metal bar?
-The molecular action of heating causes the metal to expand and generate force, which can tighten the bar. Conversely, cooling the metal causes it to contract, potentially generating enough stress to break the bar, demonstrating the power of thermal expansion and contraction.
Outlines
π₯ Thermal Expansion Experiment with Metals
This paragraph describes an experiment to demonstrate the thermal expansion of metals. The narrator introduces the concept that metals, unlike materials that burn, expand when heated and contract when cooled. A setup is presented with a wooden block, thumb tacks, a metal wire, and a needle resting on a straw pointer. The wire is heated using candles, causing it to expand and rotate the straw pointer. The experiment illustrates the energy involved in molecular movement when heated. The narrator emphasizes the magnified effect of the expansion on the needle and the importance of safety when performing a more intense version of the experiment with a blowtorch.
π οΈ Breaking a Metal Bar Through Controlled Heating and Cooling
The second paragraph details a more dramatic experiment that involves heating a metal bar with a hole at one end and a piece of metal inserted through it. The bar is tightened as much as possible to eliminate slack. The participants use blowtorches to heat the center of the bar, which causes it to expand and the slack to increase. The tightening process is repeated until the bar is extremely tight. After heating, water is poured on the bar to cool it rapidly, causing it to contract. The sudden change in temperature and the molecular action result in the bar breaking in half, demonstrating the strength of thermal expansion and contraction forces.
Mindmap
Keywords
π‘Expansion
π‘Thermal Expansion
π‘Molecular Action
π‘Kinetic Energy
π‘Pointer
π‘Candles
π‘Blowtorch
π‘Safety Glasses
π‘Contraction
π‘Slack
π‘Break
Highlights
The experiment demonstrates the thermal expansion of metals, particularly when heated.
Metals expand when heated and contract when cooled, a property not shared by materials that burn.
A wooden block with thumb tacks and a metal wire resting on a needle is used to visually represent expansion.
The metal wire's movement over the needle indicates the degree of expansion due to heat.
Candles are used as a heat source to demonstrate the expansion of the metal wire.
The straw pointer is a simple yet effective way to magnify and observe the wire's movement.
The experiment shows that even a small amount of heat can cause noticeable expansion in metals.
The energy from heated molecules causes materials to expand, as illustrated by the rotating straw.
The experiment is stopped to demonstrate the metal's return to its original state upon cooling.
A more dangerous experiment involves heating a metal bar with a hole and a piece of metal inside.
The bar is tightened as it heats up, demonstrating the effect of thermal expansion on tension.
Safety precautions, such as wearing gloves and safety glasses, are emphasized before the experiment.
The use of a blowtorch to heat the metal bar illustrates the controlled application of heat.
The bar's expansion is countered by tightening a nut to maintain tension.
The experiment concludes with the bar breaking in half when cooled with water, showcasing the power of thermal expansion and contraction.
The broken bar demonstrates the strength of molecular action during thermal changes.
Transcripts
[Music]
do you know what happens with the length
of something when you heat it well it
gets longer is that metal at least
something that doesn't burn in other
words metal when you heat it would get
longer when you cool it off it'll get
shorter it'll shrink have you ever
actually proved it no I haven't well
that's what you and I are going to do
see here's a block of wood mhm and on
top of it thumb tacks and there's a sort
of thick wire made of metal it goes all
the way over here and it's resting on
top of a needle okay and you can see the
what the pointer is made out of mhm okay
of a straw it's a straw yeah so move
this block back and forth move it that
way just slowly you see what happens to
the
needle oh it rotates and it rotates the
straw at the same time now see if you
can get it so it's hor
horizontal now here are four candles mhm
which uh will
light and
then put under the bar what should
happen to it well the bar will expand it
get longer okay and what'll happen to
the straw it'll rotate because that's
when your for you take two and I'll take
two all
right there's
one two okay
okay now slowly move the candles under
the the
wire wait a minute let me get this
exactly horizontal first okay there
okay now it should start to rotate is it
moving yeah it's
moving it's going clockwise
yeah yeah that's way down from that
horizontal already yes now that movement
isn't very much is it because we're
magnifying it as this rolls across the
needle it's rolling it and we're using a
pointer so the expansion isn't great
yeah but it's amazing how much um how
much uh energy there is when you heat
the molecules up you're forcing them to
move faster and that's what makes
something longer okay so when the
molecules are moving faster it's
expanding right okay what should happen
to the straw now keep an eye I'll blow
out the candle watch the
draw it's going back to horizontal going
back to where it was now the movement of
the molecules has a tremendous amount of
energy and we're going to put it to work
in a sort of dangerous experiment so I
want you to follow my instructions very
carefully all right first of all safety
glasses all right okay then take a look
at here's a bar mhm has a hole in the
end and see this piece of metal take it
out all right and break
it a I don't think it can be done okay
slip it back in the hole all right
through there like
that okay now I'll tighten it up here as
tight as I can get
it okay now I'm going to give you a
blowtorch and I'll take a blow torch and
we'll both heat up this Center Bar then
what's going to happen it's going to get
longer right yeah it's going to expand
okay then with the gloves on I'll
tighten this mhm to get to get to take
up that slack all right then we'll
continue to do that B two three times
until we get it nice and tight so while
you heat it up the slack is getting
bigger right
okay now have you ever used one of these
torches uh no well they're very hot
okay you can push on this lever
watch oh it heats up okay so then you
heat it over here heat the bar over here
and then when I get I tell you you move
it off to the side okay
okay
okay another quarter turn another
quarter
turn
oops I think mine went out yours went
out
too it's getting about 3/4 of a turn
okay now we've taken up all the slack
mhm pour water on the bar that we've
been heating what should happen well
it'll get smaller yeah and what'll
happen to this bar down
here well I think it might break because
it's going it's going to get really try
to break you remember how strong it was
okay pour the
water
oops there it goes
yeah good this one fell in the water so
it won't be hot there's half of
it there's the other
half you see how how strong that that
molecular action is when you heat
something and and when you cool it down
can even break a strong bar like this
right in
half
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