1.1 Vervoer

Technology

Grade 7

Transport

Module 2

Transport

For the teacher :

This unit can be done in groups.

Background

Planes fly at high speeds. They have large engines that let out a powerful source of air that propels the plane through the air. To illustrate quite simply how a plane or a rocket works, you can make a balloon fly.

Activity 1:

How to make a balloon fly

[lo 1.3]

Requirements:

• A piece of string, about 5 m long.
• Adhesive tape.
• A balloon.
• A drinking straw.
• A clothes-peg.

Method:

1. Thread the piece of string through the drinking straw.
2. Fasten the string in two places, e.g. between two chairs so that it stretches over a distance and is stretched tightly.
3. Stick two pieces of adhesive tape to the drinking straw.
4. Inflate the balloon and close the opening with a clothes-peg. Stick the balloon to the drinking straw with the two pieces of adhesive tape.
5. Move the balloon to one end of the string. Let go of the balloon by removing the peg.

What are your observations?

• The balloon with the string flies at a high speed.
• The stream of air rushes out at the opening and pushes the balloon forward. It is a reaction to an action, i.e. the movement in one direction (air that is exhausted at the rear end) causes movement in the opposite direction (balloon moves forward).

Background: How does the engine of a plane or a rocket work?

The large blades of the turbine draw air in at the front and compress it. Fuel is burned in the air and this causes the air to heat up. Following that, the warm air is exhausted at the rear end of the engine. It causes the plane/rocket to move forward at a high speed. This reaction has been known to man for almost 2 000 years, but it was only used in an engine for the first time in 1930.

The thrust exerted by moving air or water can cause objects to perform work or can even generate electricity. Air under pressure and a liquid like water can therefore be used to make things work.

The purpose of a rocket is to get a satellite or astronauts into outer space. To achieve that, gravity, i.e. the force that attracts everything to the earth, must be overcome. If the engines of a rocket are not strong, gravity will win and will pull the rocket back to earth. If the force applied by the rocket and the gravity with which the earth attracts the rocket are equal, the rocket will continue to orbit the earth.

Activity 2:

To launch your own rocket

[lo 1.3]

For the teacher:

It is better to do this experiment outside.

Requirements:

• 5 ml bicarbonate of soda.
• One sheet of paper towelling.
• 125 ml water.
• 125 ml vinegar.
• A 2ℓ plastic cool drink bottle.
• A cork that fits tightly in the mouth of the bottle with some trimming at the top.

Method:

1. Put 5 ml of bicarbonate of soda exactly in the centre of the sheet of paper towelling. Roll the sheet up and fold the ends in so that the bicarbonate of soda is tucked safely inside.
2. Take the 2ℓ plastic bottle and put 125 ml water and 125 ml vinegar in the bottle.
3. Decorate the cork with a ribbon.
4. Put the paper towel inside the bottle and put the cork on the bottle immediately so that it fits tightly, but not too tightly.
5. Stand about 3 m away and see what happens.

Observation?

The cork is blown into the air like a rocket being launched..

Conclusion:

A chemical reaction between the vinegar (representing the liquid oxygen) and the bicarbonate of soda (representing the fuel) produces the gas, carbon dioxide. The air forming in the bottle exerts pressure against the cork and causes the cork to shoot up into the air. During the launching of a real rocket, the gas is exhausted from the rocket, causing it to move forward/upward.

NB: It is dangerous to play with chemicals, and irresponsible handling of these substances could lead to serious injuries as a result of explosions or burning. Therefore, be very careful. Wear goggles to protect your eyes and only work under supervision of your educator.

Assessment