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Life's Ups and Downs

Topic: 6E Forces in action

This is a SATS revision exercise. Hot air balloons rise and submarines sink but why? Both depend on the principle of upthrust. An Indian textile millionaire reportedly broke the world record for the highest flight in a hot air balloon. The balloon soared to 21,000 metres. Balloonists need to know how to alter the weight of the balloon in order to rise or to fall. Submarines take on water in order to dive and expel it to rise to the surface.

In this activity children learn about upthrust and its effects. They label an explanation of how submarines work. They draw force arrows on a diagram of a hot air balloon and calculate how many children might be lifted.

Large activity image
 
Try the Activity Learning Objective

Click to Download Life's Ups and Downs Teachers' notes
Life's Ups and Downs Teachers' notes

Click to Download Life's Ups and Downs Activity
Life's Ups and Downs Activity

   

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· That when an object is submerged in water, the water provides an upward force (upthrust) on it

Children will demonstrate this by completing the task on page 3 successfully.

· To represent the direction of forces by arrows

Children will demonstrate this by completing the task on page 4 successfully.

· That weight is a force and is measured in newtons

Children will demonstrate this by completing the task on page 4 successfully.

   
Curriculum Link

Science:
QCA unit 6E -Forces in action

· That when objects are pushed or pulled, an opposing push or pull can be felt
· How to measure forces and identify the direction in which they act

ICT:
· Web links for further research on how hot air balloons and submarines work

 
Running the Activity

Introducing the activity
· Display page 1 through a data projector or on an OHT. Ask the children if they have any ideas about how these things work. Explore ideas such as the hot air burner on the balloon pushing the balloon up. Relate ideas expressed to previous work on forces.

Leading the main activity
· Display page 2 through a data projector or on an OHT. Print off copies for the children. Read or ask the children to read the facts aloud. Which reason do they think may be the correct one?

· Display page 3 through a data projector or on an OHT. Print off copies for the children. Revisit the idea of upthrust. Generate discussion by describing how it feels when you try to submerge a beach ball in the swimming pool and how you can feel the water pushing it up as you try to push it down. Discuss how the submarine can change weight by taking on water or by emptying the water tanks. Ask the children to work in pairs to decide which word should fit in which box.

· Display page 4 through a data projector or on an OHT. Print off copies for the children. Discuss how the hot air balloon works. Is the balloon heater on all the time? Why not? What is the purpose of sandbags? Ask the children to draw arrows on the diagram to show in which direction the forces are acting.

Q. How many children can the hot air balloon lift?

In order for the balloon to rise the upthrust needs to be greater than the weight of the balloon plus passengers

Calculation:

Upthrust = 20,000 newtons
Weight of balloon = 17 000 newtons
Therefore the difference in weight = 20, 000 - 17,000 = 3000 newtons

Each child weighs 500 newtons so 3000/500 = 6 children
However, if 6 children are added then upthrust is equal to weight of balloon plus children so the balloon will not rise

If 5 children are added then upthrust =20,000 newtons and balloon with children = 19,500 newtons
In this case the upthrust is more than the weight of the balloon plus children so the balloon will rise

A. Number of children that can be lifted = 5

 
Web Links

E-balloon
How the balloon works

BBC News
Details of balloon flight record

How Stuff Works
How hot air balloons work

Wikipedia - Hot air balloon
All about how hot air balloons work

CNN
Sonar and surfacing: how a submarine works

How Stuff Works
How Submarines Work (animation)

National Geographic
Evolution of subs - photos and facts

 
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