O.L.O.
• To recap on our forces work from last
week.
• To be able to draw conclusions from last
week’s experiment.
• To learn about another force that acts in
water.
• To understand how the shape of objects
can affect how quickly it sinks.
Forces Recap
What do we remember
from last week?
A force in water
• What is the name of one the forces
that acts upwards in water?
• What is the name of the force that
acts downwards on an object?
Upthrust and Gravity
• Upthrust is a force in water that pushes up
against an object.
• The more water moved out of the way by
the object the greater the upthrust. That’s
why ships float. Is there anything else that
helps a ship float?
• The weight of an object (gravity) is the
name of the force acting downwards.
Floating and Sinking
• Can you explain why an object floats using
the words upthrust and gravity?
• What other things help an object float
better? Think of our experiment.
• Can you explain why an object sinks using
the words upthrust and gravity?
Water Resistance
• What do we mean by water resistance? What
does resistance mean?
• Water resistance is the force that pushes against
a moving object as it passes through water.
• It is a type of friction.
• Water resistance slows the object down as they
fall through water.
Number of pennies needed to sink
boat
Boat
Diameter of Try 1
boat
Try 2
Try 3
Mean
Boat 1
4cm
14
13
13
13
Boat 2
4.5cm
15
17
16
16
Boat 3
6cm
16
16
16
16
Boat 4
6.5cm
29
28
28
28
Boat 5
14cm
132
136
120
129
Conclusions
• Boat x took the least number of pennies to sink
it.
• Boat x took the most number of pennies to sink
it.
• So we now know that the w---- the bottom of the
boat the g------ the number of pennies are
needed to sink it.
• The width and weight of the boat created more
upthrust and therefore it was harder to sink.
Water resistance in action…
• Can you think of an example of when you have
been affected by water resistance?
• When we jump into a swimming pool, it is water
resistance that prevents us from hitting the
bottom.
• How can we make ourselves get to the bottom of
the pool in the fastest time? Why?
In the pool…
• Have ever tried ‘running’ through water at
the shallow end of the swimming pool?
What is it like? Why?
• Water resistance is the force which is
responsible for making it difficult for us to
move though the water.
Predicting and Fair Testing
• Look at the different shapes of play dough and
predict which one will take the longest to sink. It
must sink and not touch the sides! Give a reason
for your choice.
• Play dough experiment – what will we measure?
• how will you make sure it is a fair test?
• Size and weight of play dough; depth of water ;
letting go of PD in same way and person timing.
Let’s investigate…
• You will investigate how the shape of an
object affects how quickly it sinks.
• In 3’s, make the shapes shown (and some
of your own)using the play dough. Lower
them into water and time how long it takes
to hit the bottom.
• Repeat 3 times for accuracy.
What do our results tell us?
• Which shape took the longest amount of
time to sink to the bottom? Why?
• Which shape took the shortest amount of
time to sink to the bottom? Why?
• Were your results what you expected?
• You could try different liquids e.g. syrup
Surface area and Stream Lining…
• The greater the surface area of the object,
the more resistance it will get from the
water.
• If we spread our body out as we jump in
the pool it will hit more water molecules.
• The amount of water resistance pushing
against him is great.
• The swimmer will sink to the bottom of the
pool much more slowly.
Streamlined…
• If we dive neatly into the water less water
will hit us and we will get to the bottom of
the pool faster.
• We are in a streamlined position.
• If we turned sideways we move through
the water quicker.
• A big splash (belly flop) more resistance…
• A little splash (tight dive) less resistance…
More streamlining
• A float helps swimmers. Have you noticed
how hard it is to swim if you stand the float
up?
• Swimmers can wear special suits made of
lycra that help reduce the amount of water
resistance.
• The amount of W.R.on a dolphin, fish and
boat are quite small – they are streamlined
and can ‘cut through’ the water easier.
Results and Conclusions
• The shape which looked this ------------took the longest time to sink. This is
because it was w-----and therefore created
a lot of water resistance.
• The shape which looked like this -------took
the shortest time to sink. This is because it
was s---------- and therefore created less
water resistance.
What have we learnt?
• What is water resistance?
• What does it do?