Grade 7 – Science
Quarter 3 – Interaction (Heat Transfer)
Heat Transfer Review
Explain the following situations using what you learned about how heat transfers.
1) What is convection?
2) What is conduction?
3) What is radiation?
4) How is heat transferred in conduction?
5) Explain how convection works for sea breezes. Do they happen
in the day or at night and why?
1) Convection is transfer of heat in a circular
movement through fluids due to differences in
density
2) Conduction is the transfer of heat through
particles in direct contact with each other passing
their vibrations along like a chain reaction
3) Radiation is the transfer of heat through energy
waves
4) Touch, molecules moving fast and bumping into
each other
5) Sea breezes happen in day. Convection occurs
because land is hotter than ocean during day (land is
better conducter than water)
6) How is heat transferred by radiation- does it need particles (air,
water, metal)? What direction can radiation move?
6) moves by waves of energy, doesn’t need particles
Can move in all directions
7) What is this called? What does it measure? Why
is one side of each paddle black and the other side
white?
7) radiometer. It measures radiation energy because
black side absorbs more energy (heat)
8) Explain how a convection oven uses a fan to work/ how is it
different than a normal oven?
8)Convection ovens use a fan or fans in the back of
the oven to move the heated air around in the oven
compartment, distributing it more evenly than a
regular oven. There is a thin layer of air that normally
insulates the food in your oven. Because a convection
oven blows the air around, it strips away that thin
layer of air, resulting in a faster cook time.
Grade 7 – Science
Quarter 3 – Interaction (Heat Transfer)
9) Why do cooks wear oven gloves when
taking food out of the oven?
9) Gloves are poor conductors
10) Why is it difficult to estimate the
temperature of things by simply
touching them?
10) temperature from hand makes it difficult due to
conduction/ temperature is relative so it depends on
if your hand is hotter or coler than the object
11) If you hold one end of a metal nail against a piece of ice, the
end in your hand soon becomes cold. Does the cold flow from the
ice to your hand? Explain.
11) No, cold does not flow. Heat flows from your
hand to the nail to the ice. Since your hand is losing
heat, it feels cold. HEAT is the only thing that flows.
12) Many tongues have been injured
by licking a piece of metal on a very
cold day. Why would no harm result if
a piece of wood were licked on the
same day?
12) Metal is a good conductor of heat, the cold metal
sucks heat so quickly from your tongue it can cause
frost bite and damage the tissue of the tongue.
13) You can bring water in a paper cup to a
boil by placing it over a hot flame. Why
doesn’t the paper cup burn?
hint: Paper burns at 451° Fahrenheit; water
boils at 212° F.
13) Since the water is considerably cooler than the
temperature needed to cause paper to burn, the
paper remains unburnt while the water boils. When
water boils, it strips away heat. The same is true of
the evaporation of water (or sweat) on your skin. It
cools. The paper cup won't burn until nearly all the
water is gone, and it's ability to take away heat is
exceeded by the flames ability to add heat.
14) The smoke will be initially hot. Since hot air is
less dense than cool air it will rise. However, it will
cool as it rises until its density is the same as the
density of the air in the room. At that point, it will
stop rising.
15) Radiation from the bulb travels quickly
14) In a still room, smoke from a cigar will
sometimes rise only so far, not reaching the
ceiling. Explain why.
15) If you turn an incandescent lamp on and off
quickly while you are standing near it, you will feel its
heat. But when you touch the bulb, it is not hot.
Explain why you felt heat from it.
16) What would happen if the furnace
was at the top of the house? Explain.
16) The bottom floors would be freezing because hot
air rises so it would all be trapped at the top of the
house
Grade 7 – Science
17) To keep your coffee hot for as long as
possible, should you add your cream first or
wait until you are ready to drink it? Why?
18) On a very sunny day you wear a black coat
and a transparent plastic coat. Which should
be worn on the outside for maximum
warmth? Explain.
19) Place cold water in a test tube. Hold the
bottom end of the test tube and heat the top
part in a flame until it boils. Why can you
still hold on to the bottom of the test tube
even when water on the top part is boiling?
20) If you wrap a piece of paper tightly around
a thick metal bar and place it in a flame, the
paper will not catch fire. Why?
21) Wrap a fur coat around a thermometer. Will the
temperature rise?
Quarter 3 – Interaction (Heat Transfer)
17) Add your cream first. The rate of heat loss
depends on the difference in temperature. The
greater the difference between room temperature
and the liquid, the greater the heat loss. Although
the cream is cool, its temperature is far closer to
room temp than the hot coffee. So its rate of heat
transfer is small compared to hot coffee cooling to
room temp. It turns out that coffee with cream
added actually cools about 20% more slowly than
plain black coffee.
18) The black coat should be worn on the inside. The
black absorbs radiant heat which would travel right
through the transparent plastic coat. And then the
plastic coat would prevent the heat from being
removed by the air by way of convection.
19) Convection- hot fluid rises so it will never go to
the botton of the testtube.
20) The metal will conduct the heat away from the
paper
21) No, the thermometer will not heat up because it
is the same temperature as the coat. There has to be
a difference in temperature in order for heat transfer
to take place
22) Explain how ‘firewalkers’ can walk safely across a bed of redhot coals in bare feet.
22) Because the rate of heat transfer is slow, because
coals are not very good conductors. If they walk fast
enough, there is only a small amount of heat
transferred to their feet, and they do not burn.
23) Where is the best place to put the air
conditioner and why?
24) put A/C close to ceiling or at top of house due to
convection cold air sinks
25) Explain the two methods of heat transfer
that makes a pot of water boil on a stove.
25) Conduction where touching the stove and
through the sides of the pot and convection in the
water itself
Grade 7 – Science
26) If you have a cup of water at 80 degrees celsius and mix it
with another cup of water at 20 degrees celsius, what
temperature will they become and why?
27) Why does blowing over hot soup cool the soup?
28) How would placing a
dented Ping-pong ball in
boiling water remove the
dent?
29) How does a
blanket keep
you warm? (hint: there are two ways)
Does it
provide you
with heat?
Quarter 3 – Interaction (Heat Transfer)
26) Take the average of 80 and 20 = 50 degrees
because of conduction spreading from hot to cold
27) Convection cooling is a very effective method of
heat transfer
28) Hot air expands and pushes the dent out
29) Keeps a layer of air above you and air is a bad
conductor (aka is a good insulator) so your body heat
stays close to you.
 Blanket also prevents convection from
happening because warm air is trapped and
can’t rise.
 No, the blanket does not provide you with
heat