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 boat

Try 1 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?