Session D: Air Resistance
Whole class teaching:
Remind
the children of their friction experiments from the previous session and the
fact that when two surfaces come into contact with each other friction occurs.
If moving over a surface is difficult then surely moving through air is easier?
Briefly discuss with the children situations where they have felt the ‘force’
of moving air – running into the breeze
on a windy day, holding an umbrella being pushed inside out, cycling on a windy
day, etc.
Give
a volunteer child a sheet of A4 scrap paper & ask them to drop it on
command from shoulder height. Use a stopwatch to record how long it takes to
fall to the ground. Record time on f/c. What happens if you change the shape of
the sheet? Does a scrunched ball fall faster or slower than the flat sheet?
What about other shapes (must use whole of A4 sheet each time)? Repeat with a
few other children.
Take
a large parachute like those used for circle time activities (in the Hall or
playground). With all the children standing in a circle start to raise and
lower the parachute together. What do they notice? – It’s hard work; the parachute feels heavier than it did when it was
still. Allow a few children at a time to lie under the parachute while it
is being raised & lowered. What do they feel? – The air rushing out and being drawn into the parachute.
Present
the children with four balls the same size - golf ball, squash ball, table
tennis ball and a bouncy ball – all same size, weigh those using digital scales
- they are all the same size but each has a different mass. Record on f/c. Ask
the children to vote for which will fall to the ground fastest when dropped
from the same height. All have the same force acting on them – gravity. Record the children’s
predictions as a tally on the board. Ask four children to come to the front to
drop them simultaneously from the same height. What do the children notice?
Repeat with several more drops… the balls fall at same rate when dropped. Why
is this? – As the shape of the balls is the same they are all affected by
the slowing air resistance in the same way. It is thought that in 1590 Galileo
climbed to the top of the leaning Tower of Pisa and performed the same ball
drop enquiry (& feather & ball enquiry)! Allow children to help
Galileo carry out his enquiry once more by going to http://www.planetseed.com/node/20129
or http://www.planetseed.com/popup/41280
(more detail). He was the first
to conclude that all objects would fall at the same rate/speed without air.
Finding an environment without air (a vacuum) is hard although space is the
perfect testing ground! See a feather and a hammer fall at the same speed at http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html.
Group activities:
Tell
the children that they are going to plan and then carry out their own enquiry
to explore how spinners weighted with paper clips fall when dropped. Before
starting they must agree in pairs on the question they are going to investigate
through discussion of the Discussion Drawing (session resource). How does
the number of paper clips affect the time the spinner takes to fall? How does
the height a spinner is dropped from, affect the time it takes to fall? How
does the size of the spinner affect the time it takes to fall?
Allow
the children to consider how they are going to carry out their experiment to
attempt to answer their questions. Remind the children that to be a fair test
they can only change one factor and must keep all others the same. Discuss with
each pair the factor that will change – greater
mass, more height, etc. Allow the children to carry out their experiment,
repeating and recording all measurements as they go. Make suggestions to groups
investigating drop heights so that this can be carried out safely. Allow students
to use template to create spinners (session
resource – this can be photocopied larger for students who choose the
option of increasing the area of paper used). Students should cut along the
dotted lines before bending one side strip forwards, one backwards to create
the blades, and folding the main body to make a triple thickness for fixing the
paper clips to.
When
the enquiry has been carried out, support the children as they create a graph
and describe any patterns created by their results. Plot a line graph. Describe
the pattern in their results, in the form: the
larger the paper spinner, the slower it fell; the more paper clips added, the
quicker it fell. Encourage the children to draw out a conclusion from their
results, e.g. air pushes upwards and
gravity pulls down; it is the size of
the air resistance force that causes objects to fall at different rates, etc.
Lesson Materials
References
Forces (Year 5) | Hamilton Trust. 2015. Forces (Year 5) | Hamilton Trust. [ONLINE] Available at:https://www.hamilton-trust.org.uk/browse/science/y5/forces-year-5/86859. [Accessed 16 November 2015].
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